MY Electronic Circuits

Basic Electronics | What is a diode?

2017-02-01T23:20:00.003-08:00

Diode is a two terminal Electronic Component with two electrodes Anode and Cathode. Diode conducts primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance to the flow of current in one direction, and high (ideally infinite) resistance in the other.Most diodes are made with semiconductor materials such as silicon, germanium, or selenium. Some diodes are comprised of metal electrodes in a chamber evacuated or filled with a pure elemental gas at low pressure. Diodes can be used as rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators.

The Primary function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). This unidirectional behavior is called rectification, and is used to convert alternating current (AC) to direct current (DC), including extraction of modulation from radio signals in radio receivers—these diodes are forms of rectifiers.

Diode working : ( Ideal Diode)

When the cathode is negatively charged relative to the anode at a voltage greater than a certain minimum called forward breakover, then current flows through the diode.

If the cathode is positive with respect to the anode, is at the same voltage as the anode, or is negative by an amount less than the forward breakover voltage, then the diode does not conduct current.

The current-voltage relationship of an ideal diode. Any negative voltage produces zero current – an open circuit. As long as the voltage is non-negative the diode looks like a short circuit.

Ideal Diode Characteristics
Operation Mode	On (Forward biased)	Off (Reverse biased)
Current Through	I>0	I=0
Voltage Across	V=0	V<0
Diode looks like	Short circuit	Open circuit

The forward breakover voltage is approximately six tenths of a volt (0.6 V) for silicon devices, 0.3 V for germanium devices, and 1 V for selenium devices.

Diode Characteristics

Free Electronic Circuit | Energy Saving lamps

2010-09-10T00:01:00.000-07:00

Ballast for energy-saving lamps

This compact ballast is intended for driving a 20-watt ‘bare’ Compact Fluorescent Lamps (CFL) tube or bulb, that is, one without a driver circuit built into its socket that makes it ready to screw into an existing lamp socket. Pin-base CFLs are designed to be used with a separate-ballast. As with a linear fluorescent system, the lamp and ballast must be compatible. Pin-base CFLs are available in low-power versions to replace incandescent light bulbs and in medium- and high-power versions to take over from linear fluorescent lamps or even high-intensity discharge (HID) lamps.

Making a pin-base CFL light

The circuit shown in Inductor picture uses a dedicated integrated circuit type FAN7710 from our friends at Fairchild. As illustrated in Figure 4, this device combines one high-side 625-V gate driver circuit, two 550-V MOSFETs, a frequency control circuit and a shunt regulator –– plus active ZVS control and an open lamp detection function, all crammed into one ultra-compact 8-way DIP package. Its high functionality and built-in protection features save board space, reduce power dissipation and guarantee enhanced reliability in end systems. Good!

The AC line input voltage (here, 230 VAC 50 Hz) is rectified to provide a bus voltage of approximately 320 volts DC. Start-up resistor R1 supplies initial (micro-) power to the FAN7710 IC. The IC begins to oscillate and the charge pump circuit consisting of C2, D2 and D7 supplies the current to the VDD pin, which gets regulated through the internal 15-V shunt regulator.

The FAN7710’s oscillator circuitry employs three discrete frequencies: one to pre-heat the CFL gas; one to ignite it and one for the on state — see the inset for the associated (simple) maths. In addition to this, it protects the ballast circuitry from low AC as well as lamp removal conditions.

Making the inductor

The bare PCB, FAN7710N IC and the 2.5-millihenryinductor used in the circuit come as a set from the Elektor Shop. However we would not discourage anyone from purchasing the inductor parts and making it yourself.

Let’s first carefully write down the specifications:

Inductance: 2.5 mH
Core material: Epcos N19 or equivalent
Core size: 20 / 10 / 6
Bobbin: E19
Gap: 1.5 mm
Wire gauge: 0.2 mm (SWG #32)
Number of turns: 280

Now look at the construction details.

First, wind the 280 turns of enameled copper wire (ECW) on the E19 bobbin. Bare the wire ends for about 5 mm by scratching with a scalpel, then pre-tin. Check continuity of the coil. Put the Ecore halves over the bobbin as shown, then insert and adjust the spacers to get the required air gap of 1.5 mm which is essential to achieve the required inductance. The final step is to wrap electrical isolation tape around the core frame.

Ballast for Energy-Saving Lamps Printed Circuit Board (PCB)

Elektor labs have designed a circuit board for the project; the component mounting plan is shown in PCB. The copper track layout is available as a free .pdf file from our website at Elektor for those wishing to etch their own circuit board. Reflected and non-reflected artwork is included in the .pdf file for your convenience. Component stuffing is a breeze as only normal size leaded components are used on a spacious board. The wiring to the mains and the lamp, and all connections and connectors in between, should comply with electrical safety guidelines. (Author: T. A. Babu, Elektor Magazine, 2008)

Caution!

The circuit is connected directly to the mains and presents lethal voltages. Relevant electrical safety precautions must be observed to prevent any component being touched while the circuit is in operation.

Free Electronic Circuit | Oxygen Sensor Simulator

2010-09-09T23:59:00.000-07:00

Oxygen Sensor Simulator

The oxygen sensor simulator as built on a protoboard. Note the cigarette lighter plug used for power source. The adjustment knob is at the left, and the switch is on the right. The red indicator LED is in the middle. Only use red, because the voltage drop of the LED is part of the circuit!

The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter(not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor(a new sensor switches more often than an old one).

The adapter cable. Note the connector recycled from an old oxygen sensor. Hard to see under the black tape: 100K resistor.

The schematic diagram of the adapter cable and oxygen sensor. Note the heater is shown as a resistor, mine measured about 7 ohms.

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Frequently Asked Questions:

Q:	Will you build one of these for me, or sell me the one you built?
A:	No, I won’t do that. If there is a community college or high school near you with an electronics class, you should contact the instructor and ask if there are students looking for a small job. This project is simple enough it should not pose a problem.

Q:	I built the project but I have to fiddle with the knob all the time.
A:	The car eventually will get too rich or too lean because it isn’t using the oxygen sensor anymore. This is a diagnostic aid, not a long-term replacement for an oxygen sensor.

Q:	I do racing on the weekends with my street car. Will this project help me tune the car to different conditions?
A:	If you do drag racing, yes. The races are short enough you can set a mixture and it will hold long enough. Each time you start the car it will go to the mixture you set. Other forms of racing take too long, and the mixture will creep towards very rich, you’d have to adjust the knob while driving.

Free Electronic Circuit | Infra-red Level Detector

2010-09-09T23:57:00.000-07:00

Useful for liquids level detection and proximity devices

Up to 50 cm. range, optional relay operation

Circuit diagram:

Parts:

R1_____________10K   1/4W Resistor R2,R5,R6,R9_____1K   1/4W Resistors R3_____________33R   1/4W Resistor R4,R8___________1M   1/4W Resistors R7_____________10K   Trimmer Cermet R10____________22K   1/4W Resistor   C1,C4___________1µF  63V Electrolytic or Polyester Capacitors C2_____________47pF  63V Ceramic Capacitor C3,C5,C6______100µF  25V Electrolytic Capacitors  D1_____________Infra-red LED D2_____________Infra-red Photo Diode (see Notes) D3,D4________1N4148  75V 150mA Diode D5______________LED  (Any color and size) D6,D7________1N4002  100V 1A Diodes  Q1____________BC327  45V 800mA PNP Transistor  IC1_____________555  Timer IC IC2___________LM358  Low Power Dual Op-amp IC3____________7812  12V 1A Positive voltage regulator IC  RL1____________Relay with SPDT 2A @ 220V switch                Coil Voltage 12V. Coil resistance 200-300 Ohm  J1_____________Two ways output socket

Device purpose:

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range can be set from a couple of cm. to about 50 cm. by means of a trimmer.
Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device's sensitivity.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the target on the same line, a couple of centimeters apart, on a short breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. This comparator switches on and off the LED and the optional relay via Q1, comparing its input voltage to the reference voltage at its non-inverting input set by the Trimmer R7.

Notes:

Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
Current drawing: LED off 40mA; LED and Relay on 70mA @ 12V DC supply.
R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.
The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
Avoid sun or artificial light hitting directly D1 & D2.
Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
If you are needing a similar circuit driving 3 LEDs in sequence, also suitable as a parking aid

Free Electronic Circuit | Car Parking Sensor

2010-09-09T23:54:00.000-07:00

Three LEDs signal bumper-barrier distance
Infra-red operation, indoor use

Circuit diagram:

Parts:

R1_____________10K   1/4W Resistor R2,R5,R6,R9_____1K   1/4W Resistors R3_____________33R   1/4W Resistor R4,R11__________1M   1/4W Resistors R7______________4K7  1/4W Resistor R8______________1K5  1/4W Resistor R10,R12-R14_____1K   1/4W Resistors   C1,C4___________1µF  63V Electrolytic or Polyester Capacitors C2_____________47pF  63V Ceramic Capacitor C3,C5_________100µF  25V Electrolytic Capacitors  D1_____________Infra-red LED D2_____________Infra-red Photo Diode (see Notes) D3,D4________1N4148  75V 150mA Diodes D5-7___________LEDs  (Any color and size)  IC1_____________555  Timer IC IC2___________LM324  Low Power Quad Op-amp IC3____________7812  12V 1A Positive voltage regulator IC

Device purpose:

This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when approaching too close to the wall.
All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity.
Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc.

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

Circuit modification:

A circuit modification featuring an audible alert instead of the visual one is available here:Park-Aid Modification

Notes:

Power supply must be regulated (hence the use of IC3) for precise reference voltages. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
Current drawing: LEDs off 40mA; all LEDs on 60mA @ 12V DC supply.
The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
Avoid sun or artificial light hitting directly D1 & D2.
If your car has black bumpers, you can line-up the infra-red diodes with the (mostly white) license or number plate.
It is wiser to place all the circuitry near the infra-red LEDs in a small box. The 3 signaling LEDs can be placed far from the main box at an height making them well visible by the car driver.
The best setup is obtained bringing D2 nearer to D1 (without a reflecting object) until D5 illuminates; then moving it a bit until D5 is clearly off. Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
If you are needing a simpler circuit of this kind driving a LED or a relay, click Infra-red Level Detector

Free Electronic Circuit | 20 Watt Automotive Power Amplifier

2010-09-09T23:51:00.000-07:00

20 Watt Automotive Power Amplifier - LM2005

The high current capability of the LM2005 allows it to continuously endure either AC or DC short circuit of the output with a maximum supply voltage of 16V. This will protect the loudspeaker in a bridge mode, when a DC short of the output occurs on one side of the speaker.

The device will prevent the speaker from destruction by reducing the DC across the load (bridge mode) to typically less than 2 VDC(VSe14.4V, RLe4X), by an internal current pullback method.

The LM2005 can withstand a constant 28 VDC on the supply with no damage (maximum operating voltage is 18V). The device is also protected from load dump or dangerous transients up to 40V for 50 ms (every 1000 ms) on the supply with no damage.

The LM2005 is a dual high power amplifier, designed to deliver optimum performance and reliability for automotive applications. High current capability (3.5A) enables the device to deliver 10W/channel into 2X (LM2005T-S), or 20W bridged monaural (LM2005T-M) into 4X, with low distortion.

Features

Wide supply range (8V±18V)
Externally programmable gain
With or without bootstrap
Low distortion
Low noise
High peak current capability
PO=20W bridge
High voltage protection
AC and DC output short circuit protection to ground oracross load
Thermal protection
Inductive load protection
Accidental open ground protection
Immunity to 40V power supply transients
Pin for pin compatible with TDA2005 (Datasheet)

Free Electronic Circuit | AC Ohmmeter - ESR Meter

2010-09-09T23:48:00.000-07:00

AC Ohmmeter - ESR Meter

The ESR Meter is basically an AC Ohmmeter with special scales and protective circuitry. It provides a continuous reading of series resistance in electrolytic capacitors. It operates at 100 kHz to keep the capacitive reactance factor near zero. The remaining series resistance is due to theelectrolyte between the capacitor plates and indicates the state of dryness. Capacitor termination problems also show up plainly due to the continuous ohmic reading.

The ESR meter uses 8 operational ainplifiers. An op-amp is an idealized basic amplifier with two inputs. The non-inverting input (+) has an in-phase relationship with the op-amp output, and the inverting input (-) an out-of-phase relationship. Op-amps are usually used with negative feedback and reach a stable operating condition when their two inputs are equal in voltage.

Op-amps IA & 1B form a regenerative 100 kHz oscillatnr circuit. Capacitor C1 is the basic tiiningcapacitor and RI is selected to set frequency. Diodes D2 & D3 clip the bottom and top of the output waveform so that the output level and frequency are resistant to battery voltage changes.

The oscillator output of op-amp 1B drives 10-ohm source resistor R8F. The test-capacitor, thru the test leads, couples this 100 kllz signal to 10-ohm load resistor R9F. The amount of voltage developed here is indicative of the capacitors ESR value. (The 10-ohm resistors determine the basic iieter scaling.)

Capacitor C3 blocks any DC voltage present on the test-capacitor. Diodes D4 & D5 protect the ESR Meter from any initial charging current to C3. Resistor R7 discharges C3 after test.

A DC operating bias of 0.55 V is established by diode D1 for the oscillator stage and for all subsequent stages, which are DCcoupled and operated class A. DC bias from D1 and ESR signal from R9F are combined at the input of op-amp 1D. Both voltages are amplified by 1D, 1C, & 2A. Each of these three stages has an amplification factor of about 2.8 due to the ratio of output-voltage to feedback~voltage at the (-) input, which is determined -by feedback resistors R13F & R14F, etc.

Op-amp 2D is configured as a peak-to-peak detector. when the in-corning AC signal goes more positive than the normal bias level of about 0.77 Volt, the output of 2D also goes positive. But it must go positive enough to overcome the voltage drop across diode D6 before a fully equalizing positive voltage can be fed back to the -(-) input thru R20 to stabilize the op-amp.

-Capacitor C4 is charged to the peak value of the AC signal and accurately represents the peak of the incoming AC signal. The voltage drop across the diode becomes almost inconsequential due to the feedback process, and the circuit works down to a few mV.

A similar action occurs during the negative peak, using D7 & C5.

Resistor R21 provides a constant minimum amount of negative feed--back around op-amp 2D. The negative feedback increases the op-amp bandwidth which, most importantly, keeps theamplifier input-to-output phase-shift low enough for proper circuit operation.

The two outputs from the peak-to-peak detector are connected to two high-input-impedance unity-gain DC amplifiers, which drive the 1 mA meter movement differentially.

Free Electronic Circuit | A Tiny pH Meter

2010-09-09T23:45:00.000-07:00

A Tiny pH-Meter

This electronic circuit is a tiny pH-meter. It is very tiny: 11cm2 including the PSU circuit! The schematic is shown below. It is basically a simple gain/offset circuit with a high impedance input (several giga-Ohm) and frankly the explanation could stop here: anyone with an background in electronics can understand this. But I started to write a webpage about this, so let's try to do it right and describe the schematic.

Juste because it's damn small does not mean that you have to settle down for second best when it comes to performance. The repeatability is around 0.01 pH and the accuracy, while depending on how well you will calibrate it, is around 0.02 pH. The main characteristics are:

very small footprint (11cm2)

very lightweight

pluggable module for easy replacement

requires only an external transformer and a display unit to work

slope/offset settings

repeatability 0.01 pH

accuracy 0.02 pH

low power

low-cost single-sided PCB

total unit price (including case and display unit): less than 100 euros.

The circuit input is pin 15 of K1. The probe signal enters IC1 via an RC circuit designed to allow only relatively slow signal variations (and avoid getting parasite HF signals). IC1 is a CMOS op-amp and thus has a very high impedance. The gain of IC1 is adjusted with the potentiometer R14. C2 is there for the amplifier stability. The R5/R11 circuit is the adjustment of the amplifier offset which is necessary for a high-precision application like this (see calibration below).

Once the signal has been amplified it enters an offset circuit built around IC2. IC2 is a more classic TL081 op-amp commonly found in audio devices, among others. The offset is defined by two potentiometers R12 and R13. The first one is on the PCB and the second one on the front panel. This improvement on the original design (single pot) allows the range swept by R13 to be symmetric, albeit smaller than without R12. It can be skipped if you wish (those small SMD trimmers can be damn expensive...). The circuit is designed to provide an average offset of 2V.

After the offset circuit the signal passes through a voltage divider before reaching the display unit. The divider roughly changes the signal range to something that is acceptable for the display. The real setting will be done on the display itself which contains a multiturn trimmer to precisely adjust its input gain.

The voltages for the signal evolve in the circuit as follows:

Before IC1: -0.414/+0.414V (this might depend on the electrode used and its age, hence the gain/offset control)

After IC1: -2/+2V

After IC2: 0-4V

After the voltage divider: 0-140mV (roughly)

After the on-display trimmer: 0-140mV

On the display: 0.00 - 14.00 pH (the display measures mV but the decimal point is placed accordingly to show a 0-14pH range)

As you can see the electrode voltage is symmetric and must undergo a linear transformation to fit the 0-14 pH range. This is all very classic stuff... Note that even if the supply rails are at +/-5V the circuit can cope with a 0-4V signal because the output swing is almost equal to the rails (no 0.7V drop, more around 0.3V IIRC).

A little remark concerning the integrated power supply circuit: it is a very small circuit that supplies a maximum of 50mA. Be careful of you want to add a power LED or something like that as it might be too much for the circuit. Check the total power used by the circuit before adding extras.PCB

The PCB is very small and you are advised to build it with through-hole mounting components if you're not familiar with SMDs. That means start the PCB design from scratch. I personally think that it looks much cooler with a small footprint... No other special remarks concerning the PCB, except that the PCBs that were manufactured were slightly different (see the photos below). This is actually also true for the schematic. No functional difference, but I changed from Protel to Eagle for designing the circuit so I had to reenter the schematic and PCB manually. Hence some differences in layout but this is not a big deal.

Component list

This is the list of components used in this circuit. I only mention the display and probe at this time as the other components are generic. Maybe more info will follow in the future.

A little link to the display unit used in this project. I chose this one because it has a nice 'pH' unit that can be activated on the display.

Another link to the probe used with this circuit (IIRC). Most probes should work but I only testedthe circuit with this one.

Construction

Random remarks: start with the smallest components, go slow, don't forget to set all the solder bridges correctly on the display unit (what you want is a 0-200mV range, an appropriately set dot and 'pH' shown as the unit). Check your cables,... before powering up.

The cabling diagram of K1 is:

* 1: AC 1

* 2: GND

* 3: +5v OUT (to display)

* 4: SIGNAL OUT (to display)

* 5: R13 / 2

* 6: R14 / 1

* 7: -5V OUT

* 8: R14 / 3

* 9: AC 2

* 10: GND (from transformer)

* 11: GND (to display)

* 12: GND (to BNC input)

* 13: R13 / 1

* 14: R14 / 2

* 15: INPUT

Free Electronic Circuit | The Leach amp 200W amplifier

2010-09-09T22:54:00.000-07:00

The Leach amp 200W amplifier

This article descripts, how I built amplifier from Mr. Marshall Leach known like "The Leach Amp". I built amplifier from the original instructions on these pages:http://users.ece.gatech.edu/~mleach/lowtim/. Article about bulding of this amplifier I found later in journalA_Radio Praktická elektronika 11/2002. For many years I looked for construction of HiFi amplifier wit a good parameters, enough power reserve and simple construction. I built a couple of amplifiers with integrated circuits MBA810, TDA2005, LM3886, but I was disappointed by their output quality and noise. I decide to built a classic construction with discrete components and bipolar transistors. Construction from Mr. Dudek was interesting, but I didn't like used components and complexity. All of my requirements satisfied construction of theLeach Amp. Circuit author publicates in a February 1976 in american journal. From these days circuit was not practically changed. Little changes are descripted on authors page.

Link to original schematics diagram: http://users.ece.gatech.edu/~mlea ch/lowtim/graphics/ckt.pdf

Local copy: ckt.pdf

Redrawed schematics diagram for use with NJL transistors with added component values:

Schematics in Eagle5 format: leachamp4_5.sch

Components

I succeeded to find almost all original components on our local market, which was a miracle. Only a bigger problem was a power transformer and filter capacitors. Recommended toroid transformer for power 200W to 4 ohms is 230V/2x 42V. I succeeded to find in a GM Electronic a toroid transformer 2x36V, 300W. Output power will be a little lower, but for home use it will be more than enough. Voltage after rectification and filtering without load will be about +51V and -51V. I couldn't find capacitors with a 10000uF or 20000uF for 75V. I decided to buy electrolytic capacitors 4700uF/63V and place four pieces parallely on positive voltage and 4 on negative voltage. I was thinking about other option to place 3 pieces of 6800uF/63V on power lines. Mica capacitors are not available at all. I used ceramic instead. Someone said, that ceramic capacitors can "play", but I didn't found any problems. Carbon resistors are allegedly better for Hifi because lower noise, but I hear it after I buyed metalised resistors. I used normal electrolytic capacitors, but probably LowESR types will be better. Power transistors are not original Motorola, or today ON semiconductor, but I didn't found any problem.

Part list for two channels
number	name	value
Transistors
12x	Q1, Q2, Q5, Q7, Q9, Q10	MPSA 06
10x	Q3, Q4, Q6, Q8, Q11	MPSA 56
4x	Q13, Q14	2N 3439
4x	Q12, Q15	2N 5416
2x	Q16	MJE 15030
2x	Q17	MJE 15031
4x	Q18, Q20	MJ 15003 (NJL3281D)
4x	Q19, Q21	MJ 15004 (NJL1302D)
Diodes
12x	D1, D2, D3, D4, D11, D12	1N4007
12x	D5, D6, D7, D8, D9, D10	1N4148
8x (15x)	D13, D14, D15, D16	20 V Zener +5% tolerance, 0.5W
Capacitors
2x	C1	390 pF mica
14x	C2, C3, C15, C16, C23, C24, C25	100nF/100V film
8x	C7, C12, C17, C18	100nF/50V film
12x	C4, C5, C13, C14, C21, C22	100uF/63V radial electrolytic
2x (4x)	C6a, C6b	220uF/16V bi-polar electrolytic (4x 330uF/16V)
2x	C8	180pF mica
2x	C9	47pF mica
4x	C10, C11	10pF mica
4x	C19, C20	10nF/50V film
Rezistors
All resistors are 1% carbonic or metalised 0,5W if not noted otherwise
2x	R1	20 kohm
2x	R2	2 kohm
16x	R3, R4, R5, R6, R7, R8, R9, R10	300 ohm
6x	R11, R12, R27	1.2 kohm
4x	R13, R14	2.2 kohm
4x	R15, R16	12 kohm
4x	R17, R18	11 kohm
2x	R19	1.1 kohm
2x	R20	22 kohm
4x	R21, R22	30 ohm
4x	R23, R24	360 ohm
4x	R25, R26	1 kohm
4x	R28, R29	270 ohm
4x	R30, R31	3.9 kohm 1/2 W
6x	R32, R33, R51	82 ohm
4x	R34, R35	330 ohm
2x	R36	220 ohm
8x	R37, R38, R39, R40	680 ohm
8x	R41, R42, R43, R44	10 ohm 1/2 W
8x	R45, R46, R47, R48	0.33 ohm 5 W wire-wound
4x	R49, R50	10 ohm, 2 W
Other
2x	P1	2 kohm more turn cermet trimmer
1x	T1	Toroid power transformer SEC 2x40V AC 300W
8x	C1P, C2P	4700uF/63V (6x 6800uF/63V 4x 10000uF/63V)
8x	C3P	100nF/200V
1x	D1P	Bridge rectifier 35A/200V
5x		Fuse casing
1x	F1	Fuse 3.15A T
4x	F2, F3, F4, F5	Fuse 5A F
8x		Insulative bed under transistors + screw insulatives 16x
20x		Solder eye M4
2m		Shrinking spaghetti 4mm

Component prepairing

To prevent DC offset problems is needed to match transistors Q1-Q4 and zener diodes. In original article is a deep description how to do it. With transistors I had not any problems at all. Probably today is their producing more precise, when they are from identical series. With zener diodes it is worse. We connect 20V zener diode in a series with a resistor on the voltage power supply that to set diode current to a 3.3mA. I discovered, that zener voltage changing according to temperature and term of connection to voltage. During measuring I tried to keep identical conditions for all diodes and I waits for steady of value after about 1 minute. I buyed more zener diodes and every piece I measured three times and write down their values. After measuring I collected diode pairs for match voltages on each board.

Next was needed to wind L1 around R49. First I doesn't know which select wire and how their best wind on the resistor. I used lacquered wire from output inductor from an old PC power supply with diameter about 1mm. I wounded 11 turns on a screwdriver with a similar diameter like a R49. Finished inductor I placed on R49, turn their ends and solder them on the resistor terminals. Resistor with an inductor is normally soldered to board.

Circuit board

circuit board layout version 4.5 which looks perfectly suitable. Circuit board is one sided, nice symmetrically designed and all components fits to them perfectly. Only one little problem was small solder spots. It's not possible to drill a little bigger holes. First piece of circuit board I redrawed to an Eagle and consequently plot it on cuprextit and etch it. Next I leave them to make at Mr. Kohout which makes simple circuit boards by photo path. I only tell him page, where was circuit board published in Aradio magazine. Concretly "Praktická elektronika A Radio - 11/2002 page 13". Because he already had film negative, that curcuit board was cheaper. Circuit board was varnished to prevent oxidation and better soldering. Before assembling is suitable to check, that all holes are sufficient for components and wires. When I increased hole on an assembled board, I little damaged a case of one electrolytic capacitor.
Original printed circuit board with heatsink drilling: http://users.ece.gatech.edu/~mleach/lowtim/graphics/layouts.pdf
Local copy:layouts.pdf
Rearranged PCB for direct assembling NJL transistors. I had to make smaller PCB than original thanks to limited Light version of Eagle, but I hope that it is OK.

Assembling

Its good to begin assembling of circuit board from the smallest components to largest. First I soldered short-circuit jumper. Next I assembled all small resistors and after them diodes. I checked resistor values and diode polarity with a multimeter before assembling. Next I assembled small capacitors and smallest, middle and largest transistors. Specially I doublechecked their position. There remaining only big resistors and electrolytic capacitors, where I specially check polarity. It's needed to right turn pins on Q16 and Q17 in line with hole position and thickness of small heat sink.

Heat sink
I couldn't find suitable heat sink for a long time. I found perfect profile at small vendor, but it was much shorter than I needed it. Finally I obtained contact on a company ALUPA, which has in their list aluminium profile which fits exactly for our amplifier. Profile has marking ZH-2476. Unfortunately I doesn't know exactly required size, that I had to cut them with a circular saw, which going very badly, because aluminium "flows". Finally I cut heat sink to lenght 15cm and drilled to them holes according to original PDF document by 4mm drill except diodes. Holes for diodes I drilled to their tight contact with heat sink. Collector of power transistors I connected from upper side with help of solder eye and thick wire. I drilled holes for wires between transistors, but it was not a good idea, because I had to a little nibble mica beds. Better will be to make holes on the side of transistors.

Transistors are attached this way: First I spread his inner side with a thin layer of silicon vaseline. Next I attached on them mica bed. Next I soldered two thicker wires long 10cm, attached a piece of shrinkage spaghetti and shrink with lighter. Wires to collectors must be longer for about 5cm. Next I spreaded mica bed from the other side too. Layer must be very thin, because vaseline tried to push out. Finally I gave transistor on his place on the heat sink, in to the holes I placed screw isolant, under one I gave solder eye with soldered thicker wire and I screw up M3 15mm screws. In to the heat sink I placed and solder up 4 diodes according to original document and I drop them with glue. I drilled a small holes in a corners of the heat sink and I made worm with a M3 screw-cutter. I placed 5mm M3 spacer leg. For better heat removal is good to place blacked heat sink vertically, but I was limited by space and technological possibilities. However I didn't see any problems with overheating.
Mechanical construction

In construction I comes again from original organization. I had available old casing from some device with height 12cm, width 48cm and depth 25cm. On the front panel is placed only power switch and four diodes. Two for positive and negative supply and two for clipping indicator of the left and right channel. Front panel from aluminium I polished, that now it looks almost like a mirror. On them is placed logo made from cuprextit and glued with both sides sealing tape. But it doesn't look much good.
Logo in a Eagle fromat
Logo in a PDF format
Toroid transformer is placed in a center close to front panel far from electronics due to interference reason. He is attached with a bigger screw to base of the chassis. Nearby is central isolated ground point and bridge rectifier. Protective ground wire is connected from the power plug to the metal chassis. Ground from plug is not connected with a central amplifier ground for preventing ground loops and interference problems.
On the left and right side from the transformer are located filter capacitors placed vertically. Between them is longer screw with a female screw and plastic hose for preventing of wearing through capacitor insulation. On the top of the screw is placed bigger rubber pad with a female screw. Capacitors are binded together. Strong power wires are from one piece of wire and goes from rectifier over all filter capacitors to fuse holders. Maybe is better to connect all capacitors with same long wires to star, but I haven't idea how to do it mechanically. Identically is made second power line and groud line from central ground point.
Circuit boards are placed in a case vertically about 3cm from back side components backward. Originally i want to place boards with components to front, but it is much difficult to solder wires to boards. Circuit boards and transistors on heat sinks are placed mirrored that input of the amplifier has very short connection wires. Boards are placed on the longer distance legs. I hadn't them, that I used longer screws with female screws. Under two female screws I had to place insulation pads, because one of wires was too close screw. All ground wires are leaded independently to central ground point.
Back panel has on one side power plug connector and fuse holder. I made mistake here, because socket is in line with speaker connector, that can conflicts with speaker wires. Beside is speaker terminal and next heat sink of the right channel screwed with four screws on the distance legs. In the middle are two gilded input cinch connectors. They must be isolated from case! Next is heat sink of the left channel and again speaker connector. R50 and C25 are soldered directly on the speaker terminals. I founded only nickeled terminals not gilded, but they are enough massive for big power. TO3 bases or insulation covers are not available on our market.
Chassis wiring

On the circuit we can see connecting of individual components in a chassis. After power socket is connected EMI filter, which reduce interference between amplifier and neighbourhood. It can be seen in compact version in the power socket. In original amplifier I haven't them. In circuit is indicated which wires are thicker. Concrete component placing is seen on photos.
Clipping indicator
It's possible to build a clipping indicator like accesory for amplifier which detects amplifier limitation, when output transistors are fully opened and signal is cutted close to power supply voltage. In this case is acoustic signal distorted in a power amplifier. Circuit as usually is from authors pages. I redraw them in a Eagle and I designed circuit board for two channels. I added place for two LEDs for power supply voltage indicators. This board have small pads, which is not much good. Eagle has these pads too small in default state.
Schematics diagram

Schematics in an Eagle
Circuit board
Circuit board in an Eagle
Circuit board in a PDF
Partlist for clipping indicator
number name value
2x Q1, Q3 BC639
2x Q2, Q4 BC640
6x D1-D6 1N4148
2x LED1, LED2 LED 2mm flat face, red
2x LED3, LED4 LED 2mm flat face, green
2x C1, C2 10uF/100V
4x R1, R2, R8, R9 12k
4x R3, R4, R10, R11 16k
4x R5, R6, R12, R13 1k5 2W
2x R7, R14 220R
2x R15, R16 22k
Testing
First we must to test power supply part. Fuses F2 to F5 we leave out and for sure we check again circuit of rectifier and capacitor polarity. a zkontrolujeme pro jistotu zapojení usměrňovače a polaritu kondenzátorů. Possible error can be fatal. If is all OK, that on capacitors will be voltage about 51V. Exact voltage depends on used transformer and power line voltage. After disconnecting will be voltage on capacitor for a long time. We can discharge them with a resistor 100R 2W. It's possible, that with power-on blows fuse F1 even all is OK. In my situation is charging current too big, that I had place NTC thermistor in a series with primary transformer side. I get them from old PC power supply, where it has identical function. Better idea is to use "soft start" circuit, which is made from big resistor on primary side of transformer and relay, which short-circuit resistor after few seconds. I didn't found any circuit which I liked it.
When the power supply works correctly, we can go to test amplifier. First we set trmmer P1 to one end position with maximum resistance. In to the fuse holders for one channel we place resistors 100R 1/4W. With disconnected output and input we can power-on amplifier. On the resistor we would measure maximally 2.5V, which matches current 25mA. If is everything allright, we wait for discharging after power-off and replace resistor with fuses. Initially for testing we can use smaller values. I had switched two wires from power transistors on one channel and resistors smokes and smells. Really is better to everything double check.
Now we must set the bias current. Use amperemeter in place of F2. Turn the trimmer P1, until is current 100mA. How amplifier warming-up current is changing. Regulate current value when it is stabilized, which can be after 15 minutes. Identical procedure repeat for second channel.
With disconnected input we can measure DC offset on the output. In my example I measured 19mV on left channel and 22mV on right channel.
Now we can made regular tests and connects speakers and signal source. I tested with connecting of the amplifier input directly on the output of soundcard. You must carefully increase volume, because amplifier has enough power to destroy small speakers.
Gallery
gallery/index.html

Partlist for clipping indicator
number	name	value
2x	Q1, Q3	BC639
2x	Q2, Q4	BC640
6x	D1-D6	1N4148
2x	LED1, LED2	LED 2mm flat face, red
2x	LED3, LED4	LED 2mm flat face, green
2x	C1, C2	10uF/100V
4x	R1, R2, R8, R9	12k
4x	R3, R4, R10, R11	16k
4x	R5, R6, R12, R13	1k5 2W
2x	R7, R14	220R
2x	R15, R16	22k

Free Electronic Circuit | USB audio DAC

2010-09-09T22:36:00.000-07:00

USB audio DAC

Introduction

I want to build high quality preamplifier with built-in DAC from SPDIF or USB for my power amplifier Leachamp. I had

available circuit PCM2902. I tried to design DAC from USB with this circuit on one-sided PCB and I was succesful.

Circuit description

Schematics is from datasheet of PCM2902. Circuit includes DAC and ADC, SPDIF output and input and HID part with

3 buttons for MUTE, VOL+ and VOL-. I used only DAC part. Other parts are not used. For high quality playback is needed to use external low-drop voltage stabiliser for DAC part. I used LP2951CM which was available at local store. Output voltage is set to about 3.7V with two resistors. Circuit board is designed regarding to good ground placement and separating of analog and digital ground. These ground are connected in one point at USB connector.

Schematics diagram

schematics in Eagle

Placement procedure

After drilling holes for crystal, output pads and USB connector I placed integrated circuit PCM2902, because I want space around him for soldering. I placed circuit at right place, soldered one pin on the side a next goes over all pins on second side and next same on first side. Almost all pins are now shorted. Now I take up tin with a solder wick. There must be enough flux on place for good disconnecting of shorted pins. After visual and electrical check we can make identical procedure with voltage stabiliser. Here is not too critical, because there are more space between pins. Next I placed SMD resistors, ceramic capacitors and LED. These parts I shoulder, that after placing on right place hold with nail, screwdriver or tweezer. One pin I solder with small amount of tin. If part still sits on right place, I solder second end and next I finally solder first end. Next I place tantal capacitors and crystal because they are big. On the end I solder USB connector. Circuit must work immediately after first connection to system a advertise like standard USB soundcard. For normal operating systems like Linux or Windows XP are not needed special drivers.

Placement scheme

Printed circuit board

Circuit board is designed one-sided and everything beside crystal and USB connector are placed from the bottom side. Circuit board is available for free version of program Eagle, which can be free downloaded from their homepage.

Postscript format Eagle format

Photos

Partlist

name	value	number
R1, R2	22R SMD 0805	2 pcs
R3	1M SMD 0805	1 pc
R4	1k5 SMD 0805	1 pc
R5	180k SMD 0805	1 pc
R6	91k SMD 0805	1 pc
R7	680 SMD 0805	1 pc
LED1	green LED SMD 0805	1 pc
C1, C2, C9, C10	10uF/35V SMD tantal	4 pcs
C3, C4, C7, C8	1uF/35V SMD tantal	4 pcs
C5, C6	22pF SMD 0805 ceramic	2 pcs
C11	10nF SMD 0805 ceramic	1 pc
IC1	PCM2902E (PCM2900E) SSOP	1 pc
IC2	LP2951CM	1 pc
Q1	12MHz crystal	1 pc
X1	USB type B connector	1 pc

External Low Pass Filter

In datasheet of PCM2902 is recommended to connect Low Pass Filter to output of DAC for filtering high frequencies above audioband which are produced by oversampling conversion. Integrated circuit includes digital LPF which filters frequency above 100kHz. In application notes for filter on the manufacturer pages are recommended 1st-Order LPF (simple RC) or 2nd-Order with operation amplifiers which works like preamplifier too. I used simple RC LPF with recommended values R 1k and C 4n7. It's better to use roll-type capacitor instead ceramic. I didn't hear difference in a sound between connection with filter or without it, but with respect to other components in a audio chain it is better to use it. For a higher cut-off frequency we can change value of capacitor to 3n3.

Interesting links

http://www.ti.com/lit/gpn/pcm2902 PCM2902 datasheet
http://www.ti.com/litv/pdf/slea048 Application report of LPF for DAC
http://www.myexposition.com/diy/usbdac/overview.html Alien DAC with PCM2702
http://www.dddac.de/ DAC with more TDA1543 circuits
http://www.cadsoft.de/ Eagle reseller

End

This DAC is relativelly simple for construction thanks to one-sided circuit board. Complementing is easy in amateurish conditions and his sound is very good with minimal interference. Sound is not crystally clean. Frequency band looks flat, but localization of individual instruments is a little worse. Maybe there can be enough to replace output electrolytic capacitors with roll-type, but this will require much space. I will try to build one more DAC without oversampling, if it will have sharper sound which I imagine for my amplifier.

Engineering Projects | 3-digit frequencymeter

2010-09-09T22:33:00.000-07:00

3-digit frequencymeter for SwissFlow flowsensor

This schematic is ment to digitally display the output of my electronic Swissflow SF800 flow sensor. This sensor puts out an open collector square wave signal (like a fan RPM monitoring signal) between 50Hz (=0.5 liter/minute) and 2000Hz (=20 liter/minute). By dividing the measured frequency by 10 and putting the decimal point at the right place you get directly a display in liter/minute. I don't use the first digit output (output D) from the 74C925 to obtain a display of 10 to 9990Hz or xx.x liter/minute. Resistor R1 (2k2) is there for accomodating the open collector output of the SF800 to a 5V TTL signal, available at connector J1.

The schematic I designed is based on a old well known Fairchild Semiconductor counter IC, the MM74C925. It's basically a 4-digit counter with seven segment-decoder & multiplexer and counter & latch registers.

The other sections of the schematic include a precise 0.5Hz timebase for the measuring time (during the positive cycle of the clock = 1 second = 1measure/2 seconds), based on a Philips HEF4521 crystal oscillator & 24-stage divider. This oscillator oscillates at 4.194308MHz and the output signal is taken from output Q23 which represents a dividing factor of 2^23 (=8.388.608) and serves as gate signal for IC3B (CD4093 NAND Schmitt trigger). Integrator IC3A creates the periodical latch enable signal and integrator IC3C produces the periodical reset signal, also from the 0.5Hz timebase signal.

The 7805 regulator delivers a stable 5V power supply from the 12V PSU line for the 74C925, the HEF4521 and the CD4093.

The segment driver output of the 74C925 is buffered by an ULN2003. With the shown values of R6-R12 (150 ohm) the peak output current per segment through the displays is about 40mA to compensate for the duty cycle of 25% and the multiplexing frequency of 1000Hz.

The 7-segment displays are (ofcourse) blue displays, the 0.56" common anode LT-5501 from Liteon. Blue leds have a forward voltage of about 3.8-4.0V, and taken into account the 0.9V saturation voltage of the ULN2003 output and the 0.7V saturation voltage of a BC327, +5V power supply was insufficient, and the displays are powered from the the +12V line. Since the digit driver outputs of the 74C925 only outputs 3 to 4 volts, it's not sufficient to saturate driver transistors T2, T4 and T6 (BC327 PNP's) and I added T1, T3, T5 (BC547 NPN's) to bypass this issue.

My Eheim 1250 pump delivers a flow of 1200 liter/minute at 0" head. Taken into account the pressure drop from radiator, water blocks, tubing and flow sensor it's quite possible that the final water flow will be under 10 liter/minute (600 liter/minute). In that case the first digit will always indicate "0". Therefore I will show both the schematics and PCB layouts for XX.X liter/minute display and for X.XX liter/minute display.

Flowmeter schematic for XX.X display

Flowmeter schematic for X.XX display

Flowmeter PCB layout for XX.X display	Flowmeter Display PCB layout for XX.X display
Download PCB layout in Circad'98 format	Download PCB layout in Circad'98 format

Flowmeter - Solder side

Flowmeter - Component side

Flowmeter Display - Solder side

Flowmeter Display - Component side

Mounted PCB's

Front view - In action

The two PCB's are soldered together by means of the solder pads at the edge of the main PCB, and the pads in the middle of the display PCB.

Fed with a square wave of 1280Hz

Idem - square wave 2630Hz

Mounted in a Lian Li bezel with blue plexi windows and together with my CPU speed indicator...

Mounted in the front panel of my PC-70...

General views of the front panel...

Engineering Projects | PIC Countdown Timer

2010-09-09T22:26:00.000-07:00

PIC Countdown Timer

Based on the April '99 project of Stan Ockers (ockers@anl.gov ), available on David Tait's archive page.
Thanks Stan!
And on the modified version by Aurelien (aurelienr@hotmail.com ).
Thanks Aurelien!
The original files (CNTDN.ZIP) from Stan are included in the download below this page.
The files from Aurelien can be downloaded from http://www.aurelienr.com (French website).

Description :

The purpose of this timer is to provide a countdown time from 1 second to 99 minutes & 59 seconds. I use it to control the lighting for the Ultra-Violet exposure of photosensitive PCB material. The project provides also an audible alarm at the end of the countdown time and switches the UV lights by means of a relay. It is based on a Microchip microcontroller, the 18 pin PIC16F84(A). This microcontroller contains 1Kbyte of flash memory for program code, 64bytes of static RAM memory, and 64bytes of EEPROM memory which are used here to store up to 15 different (user-programmable) countdown times.

The Power Supply Unit (PSU) schematic is simple and straight :
The 2x9VAC from a 3VA transformer is rectified by diode D5 & D6 and smoothed by C11 & C12 to obtain about 12VDC voltage.
This 12VDC is then used to feed voltage regulators IC5 & IC6:
- IC5 (7805 regulator) delivers the +5V voltage for the logic (PIC, 4543, relay and buzzer).
- IC6 (7808 regulator) delivers a +8V voltage to feed the four blue Common Anode displays.
If other display colours are used (red, green, yellow) the +8V power supply can be omitted and the displays feeded by the +5V for the logic.

The main schematic :
The main part in the schematic is of course the PIC16F84.
It takes care of the scanning of the pushbuttons, multiplexing the display output and activation of the relay and buzzer while running several timing routines for accurate countdown.
Fifteen countdown times can be stored into EEPROM memory. The timer starts automatically with the countdown time stored in the first EEPROM memory location.

The lower nibble of PORTA is used to drive the 4543 'BCD to 7-segment driver/decoder', the lower nibble of PORTB to drive the 7-segment digits through transistors T1 to T4.

Three push buttons allow for user input:
S1 - START/STOP push button: Starts the actual displayed count down time, or interrupts (stops) the countdown in progress.
S2 - SET push button: Allows to set the desired countdown time by litting every digit in turn (every push lits the following digit: M10,M1,S10,S1).
Waiting between pushes increments the active digit by one every second. After the last digit (second units) has been set the configured countdown time is automatically saved into the active EEPROM memory location.
S3 - SELECT push button: Allows to browse through the 15 EEPROM memory locations to retrieve the desired stored countdown time. Setting a new countdown time through the SET push button stores it automatically into the active memory location.

A 50ms beep from the buzzer confirms every key press.
At the end of the countdown time (00:00) the buzzer sounds intermittently (1Hz, 0.5sec on, 0.5sec off) until the START/STOP button is actionned, and the initial countdown time is displayed again for a next countdown.

Timer0 overflow interrupt is enabled and the prescaler (16) is assigned to Timer0. With an oscillator frequency of 4MHz this gives a Timer0 overflow (and interrupt) every 4.096 msec: 1 / [ ( 4000000 / 4 ) * 16 * 256].
When programming the 16F84(A) set the configuration word to 3FF2h : CP disabled, PWRT enabled, WDT disabled, HS oscillator enabled).

As the 16F84(A) becomes obsolete and more expensive than the 16F6x8 (16F628 with 2KB program memory, and 16F648 with 4KB) which are pin-compatible, I made also a firmware version that works with these (CNTDWN3-628-PNP.ASM), and the corresponding HEX file.
The only differences with the 16F84 firmware are:
- Initialization of PORTA as digital I/O ports (default is A/N ports).
- Relocation of the GPR (General Purpose Registers) variables from OCh to 20h.
- Modification of Indirect Addressing Pointers to point to the new GPR addresses.
- Modification of the bank selections when accessing the EEPROM memory.

When using a 16F6x8 instead of a 16F84, the 4MHz crystal (XTAL1), the 22pF capacitors (C1 & C2) and the connection of the MCLR pin to +5V can be omitted as the 16F6x8 microcontrollers series include an internal calibrated 4MHz RC-oscillator which is set by configuring the correct bits of the configuration word during programming (2149h : CPD disabled, CP disabled, LVP disabled, BOR enabled, MCLR internally, PWRT enabled, WDT disabled, Internal oscillator enabled).

Description to be continued...

Main schematic (in PDF format)

Power supply schematic (in PDF format)

PCB layout of the main board

PCB layout of the display board

PCB layout of the power supply board

Component layout of the main board

Component layout of the display board

Component layout of the power supply board

Picture of the (1st prototype of the) main board	Picture of the display board
Picture of the power supply board	Picture of the complete project

As I used an old scanner enclosure to fit the 4x15W Cleo lamps from a second hand tanning Philips device, I had to develop a new display-keyboard PCB (due to space constraints on the front panel of the scanner):

Alternate display board PCB layout

Component layout of the alternate display board

Hardware modifications on Stan's project:
- I used Common Anode displays instead of Common Cathode ones.
- I used a 4543B BCD to 7-segment decoder-latch instead of the original 4511 because of the better display of the "6" and the "9".
- BC327 PNP digit driver transistors with Icmax=0.5A instead of standard NPN transistors.
- Added relay for lamp switching (Thanks to Aurelien).
- Added ULN2003A Darlington Transistor Array on 4543 outputs (max. output for a 4511 or 4543 is 10mA/segment).
In the modified version it's about 30mA/segment to compensate for the 25% duty cycle of the displays.
- Added +5V regulated power supply.
- Added +8V regulated power supply for the ULN2003A.
- Added 10nF debounce capacitors to the pushbuttons.
- Added Piezo buzzer instead of speaker (again, thanks to Aurelien).
- Added a 555 Timer as astable multivibrator for 1Hz pulsed output to buzzer (the 555 is triggered by its reset input).

Software modifications :
- Modified BITPAT table to accomodate for Common Anode displays.
- Added initialization of PORTB and flags.
- Modified EE2D, STARTCNT and SOUNDALARM routines to accomodate for the modified INTERRUPT routine:
- In the original INTERRUPT routine from Stan, because of the bit pattern writes to PORTB (bit0 to 3), bits 4 & 5 (buzzer & relay) were always written back as 0, which needs a continuous update of these bits in the MAINLOOP & SOUNDALARM routines. This is why in the original schematic and the one from Aurelien there are 47µF capacitors through diodes to prevent the relay or the buzzer to deactivate every time the PORTB bit goes to 0.

I corrected this by modifying the INTERRUPT routine this way :
PORTB bits :
lower nibble :
b0-b3: bit pattern (=1,2,4,8 for NPN transistors, =hex 0E,0D,0B,07 for PNP transistors)
higher nibble :
b4: buzzer output
b5: relay output
b6: SET PB sense line
b7: START PB sense line

Before :

MOVF DIGIT,W ; Load digit number to lit in W
CALL BITPAT ; Get bit pattern from table
MOVWF PORTB ; write to PORTB

As you can see bits b4 & b5 are always written to PORTB as 0.

After :

MOVF PORTB,W ; Read PORTB
MOVWF TEMP ; Store result in TEMP register
MOVF DIGIT,W ; Load digit number to lit in W
CALL BITPAT ; Get bit pattern from table
XORWF TEMP,W ; Do exclusive OR with register TEMP
MOVWF PORTB ; Write result to PORTB

So bits b4 & b5 are written back to PORTB in their original state.

Files included in CNTDWN3.ZIP :
- CNTDN.ZIP : original files from Stan Ockers

- CNTDWN3PNP.ASM : Assembler program listing for 16F84 & PNP digit driver transistors
- CNTDWN3PNP.HEX : Idem in Intel HEX-format

- CNTDWN3-628-PNP.ASM : Assembler program listing for 16F6x8 & PNP digit driver transistors
- CNTDWN3-628-PNP.HEX : Idem in Intel HEX-format

- CNTDWN3PNP.PDF : Countdown3 schematic for PNP
- CNTDWN3PSU.PDF : Power Supply schematic

- CD3MB.GIF : Main board PCB layout
- CD3DISP.GIF : Display board PCB layout
- CD3PSU.GIF : Power supply board PCB layout
- CD3DISPKEYB.GIF : Alternate display board PCB layout

- MBCOMP.GIF : Main board component layout
- DISPCOMP.GIF : Display board component layout
- PSUCOMP.GIF : Power supply board component layout
- DISPKEYBCOMP.GIF : Alternate display board component layout

- COMPLIST.TXT : Component list
- CNTDWN3.TXT : This text

Also included :

- CNTDWN3PNP.CKT : Countdown3 schematic with PNP digit driver transistors in Circuitmaker2000 format
- CNTDNPSU.CKT : Power supply schematic in Circuitmaker2000 format

- CD3MB.PCB : Main board PCB layout in Circad'98 format
- CD3DISP.PCB : Display board PCB layout in Circad'98 format
- CD3PSU.PCB : Power supply board PCB layout in Circad'98 format
- CD3DISPKEYB.PCB : Alternate display board PCB layout in Circad'98 format

- Some digital JPG pictures of the finished project

Download complete ZIP file (672KB) : cntdwn3.zip

Engineering Projects | Ultrasonic Parking Sonar

2010-09-09T22:23:00.000-07:00

Ultrasonic Parking Sonar

This circuit electronic is an ultrasonic parking sonar. Based on an ultrasonic amplifier from an article seen on a 1982 magazine, it was once installed on the rear bumper of my Volvo Station Wagon. It served very well for many years. Connecting it to the reverse gear lights, it switches on automatically and shows you the distance to the nearest obstacle (according to his beam) on a led scale. When the last led lights, a buzzer is also activated telling you to stop

Feautures:

automatic switch on on rear gear

led-bargraph display

audible bleep on last led

"good old" design style, no microcontrollers!

It works on the sonar principle, sending an ultrasound burst and listening for first echo. The burst generated by the oscillator built around U4D (you must set the frequency using TR2 to have 40 kHz or the maximum sensitivity), U4E buffers the output and U4F boost the signal doubling the voltage span across the TX piezo transducer .

Engineering Projects | arm7-oled-clock

2010-09-09T22:06:00.000-07:00

B.TECH-BE Projects | Electronics

This project combines the designs for hardware and the software to make a clock with a graphic organic led display running on an atmel arm7 microcontroller.

Software is written in assembly language and is released under the GNU GPL v3 or greater:http://www.gnu.org/licenses/gpl.html

The circuit board is 2"x2" and most components are surface-mount. Hardware design files are licensed under the creative commons attribution non-commercial share-alike 3.0 license: http://creativecommons.org/licenses/by-nc-sa/3.0/us/

Here's the final write-up for the project for those interested in all the design decisions and nitty gritty: http://arm7-oled-clock.googlecode.com/files/arm7-oled-clock-project-write-up.pdf

Free Electronic Circuit | What's Electronic circuit

2010-09-09T21:52:00.000-07:00

What's Electronic circuit

An electronic circuit is an electrical circuit that connects active and passive electronic components such as resistors, capacitors, microprocessors, transistors or vacuum tubes.

The electronic circuits are typically built using a printed circuit board (PCB) that is used to mechanically support and electrically connect electronic components.
The continued miniaturization and savings in power allows electronic circuits to be packaged more densely, making possible compactcomputers, advanced radar and navigation systems, and other devices that use very large numbers of components (see microelectronics).

Electronic circuits can display highly complex behaviors, even though they are governed by the same laws as simple electrical circuits.

Electronic circuits can usually be categorized as analog, digital, or mixed-signal (a combination of analog and digital) electronic circuits.

Analog circuits
Analog electronic circuits are those in which electric signals vary continuously to correspond to the information being represented. Electronic equipment like voltage amplifiers, power amplifiers, tuning circuits, radios, and televisions are largely analog (with the exception of their control sections, which may be digital, especially in modern units).

The basic units of analog circuits are passive (resistors, capacitors, inductors) and active (independent power sources and dependent power sources). Components such as transistors may be represented by a model containing passive components and dependent sources. Another classification is to take impedance and independent sources and opamp as basic electronic components; this allows us to model frequency dependent negative resistors, gyrators, negative impedance converters, and dependent sources as secondary electronic components.

Digital circuits
In digital electronic circuits, electric signals take on discrete values to represent logical and numeric values that represent the information to be processed. Transistors are used primarily as switches to make logic gates. Examples of electronic equipment which use digital circuits include digital wristwatches, calculators and PDAs, and microprocessors.

Mixed-signal circuits
Mixed-signal or hybrid circuits contain elements of both analog and digital circuits. Examples include comparators, timers, PLLs, ADCs (analog-to-digital converters), and DACs (digital-to-analog converters).

Energy source - converts nonelectric energy into energy. examples are batteries and generators.
Output device - uses electric energy to do work and a connection. examples are motor and lamp.

3 Basic Parts
Energy source - converts nonelectric energy into energy. examples are batteries and generators.
Output device - uses electric energy to do work and a connection. examples are motor and lamp.
Connection - allows electric current to flow. examples are wire and cable.

Free Electronic Circuit | UHF RF Transmitter

2010-09-09T21:49:00.000-07:00

Very Low Power UHF RF Transmitter with CC1050 Chip

CC1050 is RF Integrated Circuit UHF transmitter designed for very low power and very low voltage wireless applications. The circuit is mainly intended for the ISM Industrial, Scientific and Medical) and SRD (Short Range Device) frequency bands at 315, 433, 868 and 915 MHz, but can easily be programmed for operation at other frequencies in the 300-1000 MHz range.

The main operating parameters of CC1050 via an easy-tointerface serial bus can be programmed, thus making CC1050 a very flexible and easy to use transmitter. In a typical system CC1050 will be used together with a microcontroller and a few external passive components. CC1050 is based on Chipcon’s SmartRF® technology in 0.35 µm CMOS.

Application Schematic and Datasheet

Features
• True single chip UHF RF transmitter
• Very low current consumption
• Frequency range 300 – 1000 MHz
• Programmable output power –20 to 12 dBm
• Small size (TSSOP-24 package)
• Low supply voltage (2.1 V to 3.6 V)
• Very few external components required
• Single-ended antenna connection
• FSK data rate up to 76.8 kBaud
• Complies with EN 300 220 and FCC CFR47 part 15
• Programmable frequency in 250 Hz steps makes crystal temperature drift compensation possible without TCXO
• Suitable for frequency hopping protocols
• Development Kit available
• Easy-to-use software for generating the CC1050 configuration data

Applications
• Very low power UHF wireless data transmitters
• 315 / 433 / 868 and 915 MHz ISM/SRD band systems
• RKE – Remote Keyless Entry
• Home automation
• Wireless alarm and security systems
• AMR – Automatic Meter Reading
• Low power telemetry
• Game Controllers and advanced toys

Free Electronic Circuit | Make Printed Circuit Boards

2010-09-09T21:46:00.000-07:00

Make Printed Circuit Boards

Creating Printed Circuit Boards (PCBs) is easy and fun for the whole family! But read the disclaimer -- heat and corrosive chemicals are dangerous. After you've prototyped and tested your circuit design, creating a PCB will provide a sturdy and reliable backbone for your circuit and will give your project a professional finished quality. Using PCBs can even help reduce the time you spend building circuits, especially if you are producing multiple units, as you only need to follow a parts placement diagram (there's no longer any need to worry about specific interconnections).

As is usually the case, there is more than one way to do it: there are numerous ways to create PCBs. They range from the time-consumming and difficult to the fully automated and expensive. Here we will attempt to describe a method we've found ideal for small production runs (say, a few prototypes to a couple of dozen--when you reach the hundreds, it will probably be easier, quicker and cheaper to outsource) of single- or double-sided boards.

Here is links for reference :
Assembly process the assembling process of sample circuit.
Chemical Etching Metals and Semiconductors.
Concepts of printed circuit design introduction to PCB technology.
Etching etching.
Etsen zonder fototechniek in Dutch
IC packages data handbook
Mounting and handling of semiconductor devices pdf file.
Photolithography photolithography.
Progressive wiring techniques
Surface Mount Technology Surface Mount Technology.
Surface Mount Technology pdf file.
Veroboard
Wire wrapping wire wrapping.
Wire wrapping how to wire wrap.

Free electronic circuit | Almost Ultrasonic Motion Sensor

2010-09-09T21:36:00.000-07:00

Almost Ultrasonic Motion Sensor | Security System

This sensor uses the sound generator in the RCX to make a 15kHz audio tone, which is almost ultrasonic. The tone is received with circuitry similar to my Sound sensor. The output of a crystal microphone MIC is amplified and then only the very high frequencies are further amplified (see plot). This signal is enveloped detected with a diode D1 and capacitor C1. The voltage on the capacitor will equal the average volume of high frequency sound the microphone is picking up at any moment. Motion of objects near to the RCX and microphone cause the volume level to vary as the signal path and distance between them changes. The variation in level is further amplified and fed to the RCX. The RCX sees a level of about 31 when there is no motion, and peaks to over 50 when there is rapid significant motion.
The circuit diagram is below. An LM324 quad Opamp is used for all stages, and the diodes are all 1N4148s.

This is a plot of the frequency response of the High Frequency Amplifier stage. The gain has been set to peak at about 15kHz so that interference from other sounds is minimized.

Here is a photo of my finished sensor. I built it on a piece of PC board and mounted it inside of a LEGO #5391 9V Battery Box. The microphone is attached to the end with double face foam tape.

Here is how I tested the circuit. The RCX has a Visual Basic program that produces a 15kHz tone and watches the input for levels over 33. If is sees one, it turns on an output which just has a light hooked up to it. The operating range depends on many mechanical factors. It can pickup motion of large objects 8" away while small objects may need to be only a few inches between the RCX and the microphone.

Here is the very simple VB code:

.BeginOfTask 0  .SetSensorType 1, 3  .SetPower "0", 2, 7  .Loop 2, 0   .PlayTone 15000, 25   .If 9, 1, 0, 2, 33    .On "0"   .Else    .Off "0"   .EndIf  .EndLoop  .EndOfTask

Free electronic circuit | Radio Wave Alarm

2010-09-09T21:34:00.000-07:00

Radio Wave Alarm | Security System

This alarm circuit is sure to have the police beating a path to your door - however, it has the added advantage of alerting you to their presence even before their footsteps fall on the doormat.

The circuit transmits on Medium Wave (this is the small problem with the police). IC1a, together with a sensor (try a 20cm x 20cm sheet of tin foil) oscillates at just over 1MHz. This is modulated by an audio frequency (a continuous beep) produced by IC1b. When a hand or a foot approaches the sensor, the frequency of the transmitter (IC1a) drops appreciably.

Suppose now that the circuit transmits at 1MHz. Suppose also that your radio is tuned to a frequency just below this. The 1MHz transmission will therefore not be heard by the radio. But bring a hand or a foot near to the sensor, and the transmitter's frequency will drop, and a beep will be heard from the radio.

Attach the antenna to a multiplug adapter that is plugged into the mains, and you will find that the Medium Wave transmission radiates from every wire in your house. Now place a suitably tuned Medium Wave radio near some wires or a plug point in your house, and an early-warning system is set up.

Instead of using the sheet of tin foil as the sensor, you could use a doorknob, or burglar bars. Or you could use a pushbutton and seriesresistor (wired in series with the 33K resistor - the pushbutton would short it out) to decrease the frequency of IC1a, so activating the system by means of a pushbutton switch. In this case, the radio would be tuned to a frequency just below that of the transmitter.

Free Electronic Circuit | Water Activated Alarm

2010-09-09T21:32:00.000-07:00

Water Activated Alarm | Security System

The Electronic circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, thetransistor will have no bias current and be fully off. As the probes get wet, a small current flows between base and emitter and the transistor switches on. A larger current flows in the collector electronic circuit enabling the 555 osillator to sound.

An On/Off switch is provided and remember to use a non-reactive metal for the probe contacts. Gold or silver plated contacts from an old relay may be used, however a cheap alternative is to wire alternate copper strips from a piece of veroboard. These will eventually oxidize over but as very little current is flowing in the base circuit, the higher impedance caused by oxidization is not important. No base resistor is necessary as the transistoris in emitter follower, current limit being the impedance at the emitter (the oscillator circuit).

Free Electronic Circuit | Audio Millivoltmeter

2010-09-09T21:28:00.000-07:00

Audio Millivoltmeter as Audio Test Equipment

When performing any tests on an audio system, some form of measuring device is essential. Digital multimeters are not useful, since they will not give the true picture of what is happening, and most have a fairly limited frequency range. An oscilloscope equipment is the ideal tool for audio test, but not all hobbyists can afford the outlay for a scope, and would find justifying the not inconsiderable cost a tad difficult.

An AC millivoltmeter - calibrated in dB - with a range of 30V down to 3mV full scale (80dB range) would be extremely useful. Attach a microphone (electret mic capsules are quite good), and you have a relative audio or sound level meter, even better if you have some way of calibration. The meter presented here has a very wide frequency range, and uses a switched attenuator for audio range adjustment. The attenuator uses the 30-10-3 sequence, which provides 10dB steps between ranges. The standard attenuator provides an input impedance of over 2M Ohms, but is a nuisance because with such high impedances stray capacitance causes havoc with the calibration, so a parallel capacitive attenuator is also needed. If you expect to work with valve amplifiers, you will want the high impedance, but otherwise the low impedance attenuator should do nicely.

The Attenuators

The two attenuator networks are shown in Figures 1 and 2, and as you can see the Hi-Z version requires all those capacitors. They must be accurate, too. Otherwise high frequency performance will be all over the place, so you need a capacitance meter or a source of close tolerance caps. Theresistors are standard E24 series 1% metal film types, and the caps (if used) should ideally be polystyrene or polyester, but if ceramic is all you can get, then ceramics are what you use. If you do have to use ceramiccaps, make sure that they have low thermal drift - NPO or similar.

Amplifier

The amplifier(s) used in such a audio test project are critical - we need wide bandwidth and low noise, coupled with low current drain, since we want to be able to run the meter on a 9V battery. The meter amplifier also requires high input impedance - especially for the high impedance attenuator version.

Complete Meter Amplifier

The entire audio test circuit can be built easily on a piece of perforated board (Veroboard or similar is good for this type of circuit), and a printed circuit board is quite unnecessary. Lay the physical circuit out following the schematic layout as closely as possible. This nearly always works well with discrete circuits, and makes it easy to follow 10 years later when you need to fix it. (I have had mine for nearly 20 years, and have not had to fix it yet.)

Test and Calibration

The initial test involves connecting the meter amp to the attenuator, and applying power. All wiring must be carefully checked before you do this - the 9V batteries can supply enough current to damage the transistors, but batteries are more expensive than the transistors, and a wiring mistake may place a heavy discharge on the batteries rendering them dead before their time. Normally, batteries should last for quite a while, since the current drain is only about 4.5mA.

Free Electronic Circuit | Audio Video Transmitter

2010-09-09T21:13:00.000-07:00

Audio Video Transmitter

Small Circuit to send your Audio Video from DVD player or satellite receiver to VHF RF signal. This circuit connected to TV RF input via 75 ohm cable or telescopic antenna. Don’t use this circuit for more power without filter and use antenna only to transmit. Frequency range on vhf band about 50-250 MHz.

You can change the transistor for transmitting on UHF band. Keep the components lead shortly. Recommended use crystal or PLL technic for stability of frequency

Free Electronic Circuit | Wideband UHF TV Signal Amplifier

2010-09-09T20:33:00.000-07:00

Wideband UHF TV Signal Amplifier

This UHF wideband signal amplifier has a total gain of 10 to 15 dB in the 400 - 850 MHz domain frequency so it can be used where the tv signal is weak. For UHF TV signal amplifier to work correctly, you need to cut the components pins as short as possible. C1, C2, C6, C7 are SMD type (surface mounted). This antenna tv amplifier or uhf wideband amplifier need to be build inside of a metal box and then connected close to the tv antenna.

The power supply is a simple 12V stabilized source. The tv antennaamplifier can be connected directly to the power supply thru coaxial cable of the tv antenna but you need a 10 - 100uH coil on the alimentation line. The tv set will be connected to the uhf amplifier thru a small coupling capacitor. Adjusting is easy, just bring the P1 to the middle and then adjust it untill you obtain the best tv image quality.

Components:

L1 = L2 = 2 turns, 3mm Ø

L3 = L4 = 10uH or 10 turns, 0.2mm Ø on ferrite

T = 2SC3358

Free electronic circuit | Video Amplifier

2010-09-09T20:25:00.000-07:00

Video Amplifier with Sync Stripper and DC Restore (EL8102)

Introduction

The circuit in Figure 1 transmits 200MHz (-3dB bandwidth) video signals while stripping off the sync pulse and performing DC restoration. It is configured for a typical video cable driver application driving a double-terminated 75Ω load, where the EL8102 (IC3) is configured for a gain of +2 to ensure unity gain throughout.

Sync Stripping

In component video systems it is frequently necessary to remove the sync pulse from an RGB signal. Sync is often combined with one or more of the red, green, and blue video signals in video distribution amplifiers, routers and switchers to decrease the number of input and output channels required in a switching network. In many applications, however, as the video signals exit the switching network the sync pulse must be removed.

The EL8102 video op amp is specially designed to perform sync stripping. Its open emitter NPN output forms an emitter-follower with the loadresistor, and passes the active video signal while virtually eliminating the negative sync pulse (see Figure 2). Residual sync of the EL8102, defined as the remainder of the original -300mV sync pulse, referenced to ground, is only 8mV at the cable output. A particular advantage of sync stripping with the EL8102 is the resultant larger (by 0.7V) output voltage swing, compared to simply using a wideband video op amp with an external emitter-follower.

Because the EL8102 contains no active pull-down, output linearity degrades as the signal approaches ground. To deal with this a 6.8kΩ pull-up resistor (R8) and a 75Ω pull down resistor (R10) on the output ensure a fixed positive voltage offset, in this case +50mV. This offset was arbitrarily chosen as a good compromise between linearity near the DC level and minimum residual sync. Increasing R8 decreases residual sync, at the expense of linearity. Conversely, decreasing R8 decreases linearity error, but increases residual sync.Other applications benefitting from sync removal are HDTV systems and video digitizing circuits. Consider a typical 1VP-P RGB video signal with a -300mV sync pulse and +700mV video data. By stripping off the unwanted sync pulse and digitizing only the active video, designers can use the full dynamic range of the A/D converter for the +700mV video data. This results in a 30% increase in resolution using the same A/D converter.

DC Restore

Another common video function is DC restoration, used when AC coupled signals have lost their DC reference and must have it periodically reset in order to retain brightness information.

This circuit accomplishes DC restoration using a CA5260 dual op amp (IC1a, IC1b) coupled with a sample-and-hold circuit based on the 74HC4053 switch (IC2). VIN, consisting of the input video signal and a DC offset (VDC), is routed to the non-inverting input of the EL8102 (IC3). The EL8102 is configured in a gain of +2 (to compensate for the attenuation resulting from double terminating the cable), which would result in an output of 2 x VIN = (2 x Video + 2 x VDC), if not for the DC restore circuit.

VIN also travels through half of the dual CA5260 amplifier to the sample-and-hold circuit, where the 0.1µF capacitor (C1) is the hold capacitor. The sample-and-hold control is triggered by a back-porch pulse from a syncseparator or by a horizontal video blanking signal. The DC output signal (VDC) from the sample-and-hold circuit is then amplified at a gain of +2 by the second op amp (IC1b); the gain is required because VDC is input to the EL8102s inverting input which provides only a gain of -1, but as discussed earlier, the output contains a term of 2 x VDC. Thus 2 x VDC is summed into the EL8102 inverting input, is subtracted from the output signal, and yields a DC restored video signal.

Because the output impedance of IC1b is high, and would affect the gain at the non-inverting input of the EL8102, a 47µF capacitor (C2) is used to provide an AC ground and to maintain good high-frequency gain accuracy.

A potentiometer (R3) is used prior to IC1b to null out any offset voltage contributed by the DC restore circuitry.

Conclusion

The circuit's resultant output is a 200MHz, DC restored video signal in which the sync pulse has been stripped to a residual level of no more than 8mV.

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Ballast for energy-saving lamps

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Free Electronic Circuit | Infra-red Level Detector

Useful for liquids level detection and proximity devices

Up to 50 cm. range, optional relay operation

Circuit diagram:

Parts:

Device purpose:

Circuit operation:

Notes:

Free Electronic Circuit | Car Parking Sensor

Three LEDs signal bumper-barrier distanceInfra-red operation, indoor use

Three LEDs signal bumper-barrier distance

Infra-red operation, indoor use

Circuit diagram:

Parts:

Device purpose:

Circuit operation:

Circuit modification:

Notes:

Free Electronic Circuit | 20 Watt Automotive Power Amplifier

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Schematics diagram

Circuit board

Free Electronic Circuit | USB audio DAC

USB audio DAC

Introduction

Circuit description

Schematics diagram

Placement scheme

Printed circuit board

Photos

Partlist

External Low Pass Filter

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End

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Engineering Projects | arm7-oled-clock

Free Electronic Circuit | What's Electronic circuit

What's Electronic circuit

Free Electronic Circuit | UHF RF Transmitter

Very Low Power UHF RF Transmitter with CC1050 Chip

Free Electronic Circuit | Make Printed Circuit Boards

Free electronic circuit | Almost Ultrasonic Motion Sensor

Free electronic circuit | Radio Wave Alarm

Radio Wave Alarm | Security System

Free Electronic Circuit | Water Activated Alarm

Water Activated Alarm | Security System

Free Electronic Circuit | Audio Millivoltmeter

Audio Millivoltmeter as Audio Test Equipment

Free Electronic Circuit | Audio Video Transmitter

Audio Video Transmitter

Free Electronic Circuit | Wideband UHF TV Signal Amplifier

Wideband UHF TV Signal Amplifier

Free electronic circuit | Video Amplifier

Video Amplifier with Sync Stripper and DC Restore (EL8102)

Three LEDs signal bumper-barrier distance
Infra-red operation, indoor use