Cool Electronic Circuits

Variable DC Power Supply LM317

2009-10-09T08:51:00.000-07:00

This DC power supply circuit is adjustable using IC Voltage Regulator LM317. LM317 is a versatile and highly efficient 1.2-37V voltage regulator that can provide up to 1.5A of current with a large heat sink. It's ideal for just about any application. This was my first workbench power supply and I still use it.

Since LM317 is protected against short-circuit, no fuse is necessary. Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all, a very powerful (and affordable!) package, indeed.

Although voltage regulator LM317 is capable of delivering up to 37V, the DC power supply output circuit here is limited to 25V for the sake of safety and simplicity. Any higher output voltage would require additional components and a larger heat sink.

Make sure that the input voltage is at least a couple of Volts higher than the desired output. It's ok to use a trimpot if you're building a fixed-voltage supply.

Problems:
Follow all the safety precautions when working with mains voltage. Insulate all connections on the transformer.

Possible uses:
Variable workbench power supply, fixed-voltage supply. Just about any possible application when no more than 1.5A is necessary.

DC- DC Converter 12V to 24V

2009-10-09T08:09:00.000-07:00

This simple circuit is a DC-DC converter that converting up 12V source to a 24V. It can be used to run radios, small lights, relays, horns and other 24V accessories from a 12V vehicle with a maximum draw of about 800mA.

This DC-DC Converter can be used to charge one 12V battery from another, or step up the voltage just enough to provide necessary overhead for a 12V linear regulator. Using one op-amp as a squarewave oscillator to ring an inductor and another op-amp in a feedback loop, it won't drift around under varying loads, providing a stable 24V source for many applications. With a wide adjustment in output this circuit has many uses.

Parts List
R1-R4,R7-R8 100K 1/4W Resistor
R5 470 Ohm 1/2W Resistor
R6 10K Linear Pot
C1 0.01uF Mylar Capacitor
C2 0.1uF Ceramic Disc Capacitor
C3 470uF 63V Electrolytic Capacitor
D1 1N4004 Rectifier Diode
D2 BY229-400 Fast Recovery Diode See Notes
Q1 BC337 NPN Power Transistor
U1 LM358 Dual Op Amp IC
L1 See Notes
MISC Board, Wire, Socket For U1, Case, Knob For R6, Heatsink for Q1

DC- DC Converter Notes
1. R6 sets the output voltage. This can be calculated by Vout = 12 x (R8/(R8+R7)) x (R6B/R6A).
2. L1 is made by winding 60 turns of 0.63MM magnet wire on a toroidial core measuring 15MM (OD) by 8MM (ID) by 6MM (H).
3. D2 can be any fast recovery diode rated at greater then 100V at 5A. It is very important that the diode be fast recovery and not a standard rectifier.
4. Q1 will need a heatsink.

Source : 12V To 24V DC-DC Converter Circuit

NiCad Battery Charger

2009-10-09T07:12:00.000-07:00

This battery charger circuit is designed for recharging NiCad batteries based on an AC-powered current source method. It can crank out as much as 1 amp and can be modified to go even higher by choosing different devices for Q1. Since this circuit uses AC line voltages and currents, please exercise extreme caution during assembly, turn-on, and test.

NiCAD batteries have a capacity specification called milliamp-hours. This value called "C" is a measure of how much total current they can provide in one hour. Milliamp-hours is another way to express the energy contained in the battery. To recharge a NiCAD battery conservatively, it is common practice to pump a current of 0.1 C into the anode or positive terminal for about 12 hours. Therefore, if you had a D-size NiCAD with a capacity of 4000mAh, you would want to charge it at 400mA for about 12 hours. Another advantage of this charging technique is that it is gentle on batteries and doesn't cause them to lose capacity as quickly as the fast charge techniques.

The output current of this battery charger circuit is controlled by the summation of the bandgap reference diode and the base-emitter junction of the PNP transistor. The PNP transistor provides negative feedback to the gate of the MOSFET. As noted in the schematic, the batteries being charged can have a total of 12V which is equivalent to about 8 NiCAD's in series. The output current is determined by the value of R1 which is determined by:

R1=3.2Volts/Iout

The power dissipation of R1 will equal:

Pr1=3.2Volts*Iout

Be sure to provide pleanty of heatsink for Q1 and choose an appropriately sized resistor for R1. The following table summarizes some of the resistor current combinations that are possible:
Iout Resistor Value Resistor Power

100mA 33 ohms 1 watt

500mA 6.2 ohms 2 watt

1Amp 3.3 ohms 5 watt

Source: Battery Charger

Laptop Power Supply for Car 95W

2009-09-22T07:27:00.000-07:00

A laptop or notebook computer user while they are away from the home or office knows that sooner or later they will need to plug into a mains outlet to top up the batteries. The car cigarette lighter socket in the car is also an electrical outlet but it can only supply 12 V. That’s no problem for the Laptop Power Supply described here.

The laptop power supply described here plugs into a car cigarette lighter socket and produces a 19V nominal output voltage adjustable by + - 0.5V. The input voltage range is from 9.2V to 15V and the output voltage shows good regulation even with large fluctuations of the input voltage. The output can supply 5A continuosly with brief excursions up to 10A.

The power semiconductor heatsinks of this laptop power supply are dimensioned fo 5A continuous so extended operation up to 10A will increase dissipation in the adapter and in extreme cases will cause the input fuse to complain.

Laptop PSU Adaptor Parts List
Resistors:
R1 = 5k6
R2 = 51k (51k1)
R3 = 9k1 (9k1)
R4 = 1M
R5 = 4k7
R6,R8 = 15k
R7 = 27k
R9,R10 = 6,8
R11 = 10k
R12 = 100
P1 = 5k preset
Capacitors:
C1-C4 = 3300µF 16V, radial, low ESR, diam. 12.5 mm, e.g. Panasonic EEUFC1C332 (Farnell)
C5,C10 = 1µF MKT, lead pitch 5mm or 7.5mm (larger version preferred)
C12 = 1µF MKT, lead pitch 5 mm
C6-C9 = 2200µF 25V radial, low ESR, diam. 12.5mm, e.g., EEUFC1E222 (Farnell)
C11 = 22nF, lead pitch 5mm
C13 = 2nF2, lead pitch 5mm
C14,C15 = 100nF ceramic, lead pitch 5mm
C16 = 10µF 63V radial
Inductors:
L1 = 56µH, 21 turns 10 x 0.5 mm ECW, parallel
1 x ETD 29 coil forner, vertical mounting, Epcos B66359X1014T1 (Schuricht # 331622)
2 x ETD 29 clamp, Epcos B66359-A2000 (Schuricht # 333862)
2 x ETD 29 core half, material # N67, air gap 0.5mm, Epcos B66358-G500-X167 (Schuricht # 333840)
Semiconductors:
D1 = MBR1645 (International Rectifier) (e.g. Reichelt, Segor)
T1 = IRL2505 (International Rectifier) TO-220AB case, (e.g., RS Components)
T2 = BD139
T3 = BD140
IC1 = UC3843N (Texas Instruments) (e.g. Reichelt, Segor)
Miscellaneous:
K1-K4 = 2-way spade terminal, vertical, PCB mount
F1 = fuse, 10A/T (slow) 6.3 x 32 mm (¼ x 1¼ inch) + 2 fuse holders for 6.3 mm diameter and PCB mounting
2 x heatsink type SK104-STC (or STS) TO220 38.1mm, 11K/W (Fischer Electronic) Isolating washers for T1 and D1 (TO-220AB) + isolating bushes
PCB

Laptop PSU Adaptor PCB-Layout

Source: Laptop Power Supply Adaptor 95W

Power Converter 12 VDC-220 VAC 50W

2009-09-22T06:50:00.000-07:00

The power converter circuit is aimed to convert 12 VDC to 220 VAC and the process known as inverter. By inverting process will produce a 50W power converter that would supply different small appliances.

The DC to AC inverters are widely used in rural electrification the require AC power which includes solar home systems, health clinics, and community centers. Power Converter can also be used for other photovoltaic systems that convert light energy into electricity such as weekend homes and remote cabins, boats and caravans, and small telecom photovoltaic systems.

Power Converter Circuit Explanation
The power converter circuit is constituted by the oscillator, round the IC1, one divider IC2, one unstable multivibrator IC3, which give in the output symmetrical square signal of frequency 50HZ, follow a buffer stage with Fet Q1-2, the drive stage Q3-4 and the power stage Q4-5, the power transistors Q5-6, should they are placed in heatsink.

The diodes Zener D2-3, protect the power transistors from voltage peaks, that are produced by the transformer T1. Transformer T1 are a simple power transformer, with intermediate reception, which is connected in the contacts of CO1. For the use that him we want, the T1, is placed in reverse, with secondary convolution it is used as primary, with the intermediate reception she is connected in the positive point of battery 12V and the two other contacts are connected in the emitters of Q5-6, that are connected in the potential of ground alternately, depending on the rythm that determine outputs 10 and the 11 from IC3.

With this way while in being primary flow AC current, in secondary is created 220V AC square voltage. The use of crystalic oscillator ensures very good reference frequency 50HZ, and use a simple crystal (CR1). For bigger precision, parallel with the C1, exist a variable capacitor Cx, that ensure the regulation of frequency, so that we take in point P1, frequency 204.8 KHZ.

It's obvious that the output voltage in void of load is bigger than the voltage with load. Also the output voltage depend from the output voltage of battery. Thus for battery voltage 14V, the output voltage is increased at 10%, compared to the battery voltage 12V. If the converter work in load power 40 until 60W, then it can be used transformer 2X9V. Various prices of output, for battery voltage 12V and transformer 2X10V,

Power Converter Parts List
Resistor
R1=10Mohms
R2=100ohms
R3=1.2Kohms
R4=560Kohms
R5-6=2.2Kohms
R7-8=56 ohms 5W
Capacitor
CX=22pF trimmed capacitor
C1-2=22pF ceramic
C3=8.2nF 100V MKT C4=10uF 16V
C5=47uF 16V
C6=470nF 400V
Diode
D1=5V6 0.4W
D2-3=47V 1W
Transistor
Q1-2=BS170
Q3-4=BD139
Q5-6=BD249
Integrated Circuit
IC1=4060
IC2=4013
IC3=4047
Crystal
CR1=3.2768 MHZ crystal
Transformer-Fuse
T1=220Vac/2X10V 2X2.2A
F1=5A Fuse
F2=0.25A Fuse
Inductor
L1=1H smoothing choke

Power Converter Printed Circuit Board Layout

Source: 12VDC to 220VAC_Converter

VHF FM Receiver TDA7000 88-108 MHz

2009-09-18T18:02:00.000-07:00

Here is a very simple VHF FM receiver which is little more than a single IC and a "slack handfull" of capacitors. Note that an external amplifier is a really necessity since the unit only delivers about 70mV of AF.
See High Power FM Wireless Microphone transmitters, probably because it is so simple too.

The 10K resistor (*) is only required if you want the receiver to mute (squelch) under no-signal conditions. You could add a 100K in series with this resistor to get an adjustable squelch. This circuit will JUST drive a crystal earphone or high impedance headphones directly, but an output isolating capacitor (100nF) is needed for any other device. L1 is 6 turns No 18 SWG enamelled wire on a 5mm former, but you may have to play with the values a bit. I used a coil fabricated on the PCB itself, tuned with a trimmer capacitor.

All the other components are just a bunch of capacitors which are fitted to the board at the other side of the chip, just to make it look a bit prettier.

As you can see, this receiver is VERY sensitive, small and seems to work very well indeed. It is in fact a full superhet receiver with a very low RC tuned IF. The Image signal is rejected by the action of the AFC which functions to push it away. With suitable antennas and terrain, with this receiver you could easily get the full 500 meters from the FM wireless microphone v5. I am offering this receiver in kit form, including solder, antenna wire etc. All you will need to provide is the battery, tools and soldering iron. Here is the kit version fully assembled.

The total size is 45mm x 48mm. If there is any interest in the kit then I may even add an AF amplifier kit so that you can make a full bedside/table radio.

Source: TDA7000 RX

High Power FM Wireless Microphone

2009-09-18T17:50:00.000-07:00

This FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike. It has been used inside guitars and as the basis of a remote control system. I do however, receive many requests for a higher powered circuit and better microphone sensitivity.

This High Power FM Wireless Microphone has a better frequency stability, over 1 Km range and is good on microphone sensitivity. This has been achieved by adding an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little.

Construction is quite simple. L1 is 3.25 turns in spiral form and is an integral part of the PCB foil pattern. The two BC547 transistors can be replaced with (almost) any small-signal NPN transistor, such as the 2N2222. The final stage is a BC557 PNP general purpose device. If you use different devices then you should select the 1M0 resistor for 5-volts DC at the collector of the the first transistor. Select the 47K resistor for 3 - 4 volts on the collector of the third transistor. Here is the V5 component overlay drawing. Note that there is a modification:

The PCB is 50mm x 25mm, a little larger than the first version but there are three stages instead of just the one. The first prototype is shown above, beside the battery powering it. The output power is about +10dBm which is about 10dB more than the first FM Wireless Microphone. This would theoretically give it 3.12 times the range (1.6Km) but I have only tested it using a handheld receiver with the TX laying on the bench indoors. But I got a comfortable 700 meters (and a few funny looks from our neighbours).

Above you can see the addition of a "gimmick" capacitor added across the 12p tuning capacitor to lower the frequency of the transmitter. Make the capacitor by twisting two lengths of single core insulated hook-up wire, about 2cm long. This will reduce the frequency to the bottom end of the band. Cut short the capacitor to increase the frequency to the desired final frequency. If you cut it a few KHz too high then just twist the gimmick a little tighter.

The PCB foil pattern and layout will be placed in the download section of my homepages. Have fun and please be aware that the higher power of this project may render it ILLEGAL in your own country. I can accept no responsibility and it is up to you to check that you may legally use it. I will accept NO complaints from any country/state correctional facility.

Source: High Power FM Mic

LED Power Meter Using Digital Multimeter

2009-09-18T16:44:00.000-07:00

LED power Meter circuit is a simple RF detector using diodes to charge a capacitor. The voltage developed across the capacitor is indicated by a multimeter set to a low voltage range. The circuit is soldered together without the need for a PC board, as can be seen in the diagram below and paper clips are used for the positive and negative terminals of the multimeter.

The level power output of an FM transmitter is indicated by the illumination of a LED and the voltage reading on the multimeter gives a further indication of the output.

A digital multimeter may be used but the presence of RF may produce a false reading. Likewise, the radiated energy may upset some analogue meters and you may get full scale deflection on the 15v range as well as the 250v range! But the LED won't lie. It will accurately indicate the RF and you can see the change in brightness as you adjust the coils in the output stage. Some of the cheapest and simplest multimeters will give the best results as they have a low sensitivity and the radiated RF energy will not induce a reading. Even a damaged multimeter can be used, provided the 10v or 15v DC scale is operating.

The reading is not calibrated and does not represent milliwatts output. It is only a visual indication.
We have designed over 10 FM transmitters for inclusion in the pages of this e-magazine and each one has different features and characteristics. Some are designed for 3v operation, some are for 9v operation, some are stable for hand-held situations and others are designed for high output. The illumination of the LED will range from barely visible to very bright.

LED Power Meter Parts
1 - 470R
1 - 100p ceramic
1 - 100n ceramic
2 - 1N 4148 diodes
1 - 5mm Red LED
1 - 2in (5cm) hook-up wire
2 - paper clips
No PC board required

Read more: LED Power Meter

LED Indicator Relay Timer Circuit-9 Second

2009-09-15T03:59:00.000-07:00

This Relay Timer circuit provides a visual time 9 second delay using ten LED before control by closing a 12 VDC relay. That the reset switch has closed, IC 4017 decade counter will be reset to zero count which illuminates the LED driven from pin 3.

IC 555 timer output at pin 3 will be high and the voltage at pins 6 and 2 of the timer will be a little less than the lower trigger point, or about 3 Vdc.

That time the switch is opened, the transistor in parallel with the timing capacitor (22uF) is shut off allowing the capacitor to begin charging and the IC 555 timer circuit to produce an approximate one second clock signal to the decade counter. The counter advances on each positive going change at pin 14 and is enabled with pin 13 terminated low. When the 9th count is reached, pin 11 and 13 will be high, stopping the counter and energizing the relay. Longer delay times can be obtained with most capacitor or most resistor at pins 2 and 6 of the IC 555 timer

Source: 9 Sec Timer with LED indication and Control Relay Circuit

Variable Dual Power Supply LM317-LM337

2009-09-15T03:37:00.000-07:00

This is a bench top power supply that can be used to power circuits or devices during development work in the lab. More specifically it is an adjustable, tracking, dual rail supply which means there are two supply voltages, one positive, one negative, that are adjusted by a common potentiometer such that supply voltages are equal in magnitude. It is capable of supplying up to +/- 15V DC at up to 1A. This is sufficient for the majority of small signal electronic projects.

Power Supply Schematic

Power Supply circuit above shows the circuit layout for this project. A centre tapped transformer (TR1) is used with two 12V secondary windings with its centre tap tied to ground. This allows positive and negative voltages to be generated with respect to the central ground. Rectification follows based upon the bridge rectifier (BR1) and smoothing capacitors (C1, C2, C4 and C5).

Two linear regulators are used, an LM317 on the positive side and an LM337 on the negative side. These regulators keep the supply voltage constant for a varying load up to a load current of around 1A. The voltage adjustment is achieved through potentiometers RV1 and RV2 in the positive side of the circuit. The clever part of this circuit comes from the mirroring of the positive voltage adjustment to the negative side via the op-amp U2 to give the circuit its tracking nature.

The op-amp U2 has its positive input tied to ground via a 4K7 resistor. This means that, providing there is negative feedback around the op-amp, the op-amp will endeavour to make its negative input also at ground or 0V. The negative feedback is arranged by the output of the op-amp U2 driving the Adjust pin of the negative regulator U3 and by resistors R3 and R4. The op-amp U2 sets the voltage on the adjust pin of U3 such that the voltage at its negative input is 0V. Also as R3 and R4 are equal, the positive and negative regulated voltages must then be equal in magnitude.

An analogue meter is driven from the positive side to give an indication of the voltage setting. Two switches are used to allow the positive and negative supplies to be turned on/off independently and there are also two LED acting as indicators.

Dual Power Supply Construction

This power supply circuit was built up on Veroboard as it is quite simple to build. Heatsinks can be mounted to the two regulators to improve the current drive capability. The transformer and circuit were mounted inside a wooden box. If a metal box is used the box must be connected to mains earth to prevent a shock hazard. Figure 2 shows a picture of the finished unit. It should be noted that this box is rather shabby and the author has been meaning to improve it for a while but it does do the job nicely.

Source: Tracking, Dual Rail Power Supply

Thermistor Temperature Monitor Circuit

2009-09-11T12:17:00.000-07:00

Here's a simple op-amp circuit with a NTC thermistor as sensor that will trigger a relay when a preset temperature is reached. There is no hysteresis in this circuit, so that if the temperature changes rapidly, then the relay may switch rapidly.

This sensor circuit uses an ordinary NTC thermistor with a resistance of 47k at room temperature. A suitable part from Maplin Electronics is FX42V. The circuit is set in balance by adjusting the the 47k potentiometer. Any change in temperature will alter the balance of the circuit, the output of the op-amp will change and energize the relay. Swapping the position of the thermistor and 47k resistor makes a cold or frost alarm.

At room temperature (25 degrees Celsius) a 47k NTC thermistor resistance is approximately 47k. The non-inverting op-amp input will then be roughly half the supply voltage, adjusting the 47k pot should allow the relay to close or remain open. To calibrate the device, the thermistor ideally needs to be at the required operating temperature. If this is for example, a hot water tank, then the resistance will decrease, one way to do this is use a multimeter on the resistance scale, read the thermistors resistance and then set the preset so that the circuit triggers at this temperature.

Please note that if the temperature then falls, the relay will de-energize. If the environment temperatures changes rapidly, then the relay may chatter, as there is no hysteresis in this circuit.

Hysteresis, allows a small amount of "backlash" to be tolerated. With a circuit employing hysteresis, there will be no relay chatter and the circuit will trigger at a defined temperature and require a different temperature to return to the normal state. Hysteresis can be applied to the circuit using feedback, try a 1 Mega resistor between op-amp output, pin 6 and the non-inverting input pin 2 to give the circuit hysteresis.

Without offset null adjustment, the output of the 741 IC will be around 2 Volts (quiescent) swinging to nearly full supply when triggered. The 4.7k and 1k resistor form a potential divder so that under quiescent conditions the transistor will be off. Quiescent or steady state means no signal, or in this case (when the temperature does not cause the output to swing to full voltage).

Source: Temperature Monitor

Analog Milliamp Meter Used as Volt Meter

2009-09-07T21:33:00.000-07:00

By adding a series resistance, a milliamp meter can be used as a volt meter. The resistance needed is the full scale voltage reading divided by the full scale current of the meter movement. So, if you have a 1 milliamp meter and you want to read 0-10 volts you will need a total resistance of 10/.001 = 10K ohms.

The meter movement itself will have a small resistance which will be part of the total 10K resistance, but it is usually low enough to ignore. The meter in the example below has a resistance of 86 ohms so the true resistor value needed would be 10K-86 or 9914 ohms. But using a 10K standard value will be within 1% so we can ignore the 86 ohms. For a full scale reading of 1 volt, the meter resistance would be more significant since it would be about 8% of the total 1K needed, so you would probably want to use a 914 ohm resistor, or 910 standard value.

By adding a parallel resistance, the milliamp meter can also be used to measure higher currents . The meter resistance now becomes very significant since to increase the range by a factor of ten, we need to bypass 9/10 of the total current with the parallel resistor. So, to convert the 1 milliamp meter to a 10 milliamp meter, we will need a parallel resistor of 86/9 = 9.56 ohms.

Source: Analog Milliamp Meter Used as Voltmeter

Digital Metronome ATMEL AT92S1200

2009-09-07T20:55:00.000-07:00

A metronome is a device used by musicians to keep a steady pulse or beat while performing a piece of music. The measurements on a metronome are marked in beats per minute or BPM. A tempo marking of 60 beats per minute would be the same thing as one beat of music every second. Likewise 120 beats per minute would be two beats every second.

The main purpose of a metronome is to help the musician learn their music at the proper speed, usually so that they can then combine their part with other players in an ensemble

The digital metronome has following features:

ATMEL AT92S1200(or higher) based: AVR 8 Bit RISC processor with timer.
Range: 22.8 to 216 beats per minute w/ variable tuning-steps. Presets on 60, 120 and 180 bpm.
Measure feature: an extra beat per 2/4, 3/4, 4/4 (the "measure").
Precision: calibrated for 1MHz clocks and using timers (INTERUPT BASED). Other clocks possible.
Load: approx. 20mA (due to driving the LED segments).

It is basically the processor with buttons and led and audio I/O, together with 4 LED segments. There are 3 segments for the BPM ("beats-per-minute") read-out and 1 for the 'measure' (2/4, 3/4, 4/4, disabled).

SEGMENT #0: not used
SEGMENT #1: the measure (output is 2 , 3 , 4 or 1 for 2/4, 3/4, 4/4 or NONE)
SEGMENT #2-4: LED x1 (#2) , x10 (#3) and x100 (#4).

Metronome Schema and Source Code

Metronome Main Schematic

4 Segment Driver Schematic

Processor ATMEL AT92S1200 pin Layout The audio section produces a nice sound (which can be muted).

METRONOME: the assembler program for the AT92S1200 (or better) microprocessor.

Source: PROJECT: A Digital Metronome

Digital Blood Pressure Meter

2009-09-06T01:35:00.000-07:00

This Digital Circuit describes a Digital Blood Pressure Meter concept which uses an integrated pressure sensor, analog signal-conditioning circuitry, microcontroller hardware/software and a liquid crystal display. The sensing system reads the cuff pressure (CP) and extracts the pulses for analysis and determination of systolic and diastolic pressure. This design uses a 50 kPa integrated pressure sensor (Freescale Semiconductor, Inc.P/N: MPXV5050GP) yielding a pressure range of 0 mm Hg to 300 mm Hg.

CONCEPT OF OSCILLOMETRIC METHOD
This method is employed by the majority of automated non-invasive devices. A limb and its vasculature are compressed by an encircling, inflatable compression cuff. The blood pressure reading for systolic and diastolic blood pressure values are read at the parameter identification point.

The simplified measurement principle of the oscillometric method is a measurement of the amplitude of pressure change in the cuff as the cuff is inflated from above the systolic pressure. The amplitude suddenly grows larger as the pulse breaks through the occlusion. This is very close to systolic pressure. As the cuff ressure is further reduced, the pulsation increase in amplitude, reaches a maximum and then diminishes rapidly.

The index of diastolic pressure is taken where this rapid transition begins. Therefore, the systolic blood pressure (SBP) and diastolic blood pressure (DBP) are obtained by identifying the region where there is a rapid increase then decrease in the amplitude of the pulses respectively. Mean arterial pressure (MAP) is located at the point of maximum oscillation.

HARDWARE DESCRIPTION AND OPERATION
The cuff pressure is sensed by Freescale's integrated pressure X-ducer‰. The output of the sensor is split into two paths for two different purposes. One is used as the cuff pressure while the other is further processed by a circuit.

Since MPXV5050GP is signal-conditioned by its internal op-amp, the cuff pressure can be directly interfaced with an analog-to-digital (A/D) converter for digitization. The other path will filter and amplify the raw CP signal to extract an amplified version of the CP oscillations, which are caused by the expansion of the subject's arm each time pressure in the arm increases during cardiac systole.The output of the sensor consists of two signals; the oscillation signal ( ≈ 1 Hz) riding on the CP signal ( ≤ 0.04 Hz).

Hence, a 2-pole high pass filter is designed to block the CP signal before the amplification of the oscillation signal. If the CP signal is not properly attenuated, the baseline of the oscillation will not be constant and the amplitude of each oscillation will not have the same reference for comparison.

Oscillation signal amplifier together with the filter.

Digital Blood Pressure Meter Schematic

Author: C.S. Chua and Siew Mun Hin, Sensor Application Engineering Singapore, A/P
More about Digital Blood Pressure Meter

Battery Booster Circuit

2009-07-28T20:41:00.000-07:00

The inspiration for this design came from the author’s experience with a mini model helicopter (from Silverlit). This particular model has a hand-held transmitter powered by six AA batteries which acts as a charging station in between flights to recharge the helicopter’s LiPo battery.

Even alkaline batteries become discharged relatively quickly because of the energy demands of the helicopter. Replacing the alkaline cells with six rechargeable NiMH batteries brought its own problems; the cell voltage is around 1.4 V after recharging but this quickly levels-out to 1.2 V once you begin drawing energy and this proved to be too low to recharge the helicopter battery. What is needed here is a voltage converter design small enough to fit into the space taken up by an AA battery which pumps up the voltage from the (now five rechargeable cells) up to the level produced by six alkaline batteries.

The author was not satisfied with the most simple design solution to the problem; it would be more useful if this booster cell could be used in any battery compartment irrespective of the number of cells. The number of batteries (n) would then be replaced by n–1 rechargeable cells (with one cell position taken up by the booster) giving an output voltage the same as if n primary cells were fitted.

The circuit described here can be used in applications requiring four to ten primary cells. With the booster fitted, only three to nine rechargeable cells would be required. The use of (more bulky) electrolytic capacitors with a 35 V rating would allow the booster to be used in applications of up to 20 batteries.

In principle almost any switching regulator IC can be used in this way. The power output from this circuit with a LT1172 regulator is around 500 mA but it can be increased to 2 A for example by using the LT1170 instead.

LNB Cable Data Transceiver Circuit

2009-07-28T19:33:00.000-07:00

This circuit was designed and used to transmit commands over LNB coaxial cable. An LNB (or LNC) is a low-noise block downconverter typically used for satellite TV reception. It’s fitted in the focal point of a satellite dish.

The circuit is based on generating a modulated signal on the bus which can be decoded by a tone decoder IC like the familiar LM567 from National Semiconductor.Data and carrier signals are ORed using D1 and D2. T1 acts as a current source whose current depends mainly on the value of R3.

L1 and C5 form a (damped) resonance circuit for the centre frequency of the carrier. C6 acts as a very low impedance bypass, so the impedance seen by T1 at the carrier frequency equals roughly R4. As the current passes through R4, the voltage generated across it can be detected by IC1 which has its input coupled to the bus via C4. The low DC resistance of inductor L1 allows current to flow to the circuitry connected to the bus.

Components R1 and C1 control the centre frequency of the decoder, and C2 the bandwidth. Relevant formulas may be found in the LM567 datasheets. C3 is output filter and its value depends on the ‘data’ frequency.

In accordance to what’s found in the LM567 datasheet, the carrier frequency must be at least 20 times higher than the frequency of the ‘data’ signal. The maximum detectable carrier frequency is about 500 kHz. R5 is just a load for IC1, whose output is signal in phase with ‘data’. The Carrier frequency can be generated using any simple square wave generator.

In the author’s application, the carrier frequency was 100 kHz with 1200 bps data, both generated by a microcontroller. The transmitter and receiver were installed at each side of the LNB cable to create a half-duplex transceiver. Author: Sajjad Moosavi.

12V Travel Water Heater 2N3055

2009-07-28T19:10:00.000-07:00

I have gone through about seven of those spiral immersion water heaters that operate from 12V DC. Most of them didn’t even last as long as a trip by car to and from the south of France.

After a bit of experimenting with resistors, incandescent lamps and other electronic components that can give off heat and might be able to last longer than these immersion-type travel water heaters, I found the answer in the form of the trusty 2N3055 transistor in its TO-5 package. It has a maximum operating temperature of 200 °C and a maximum rated dissipation of around 115 watts.

The power level can be set with a single resistor between the collector and the base, so the circuit consists of just two components aside from the cable and plug. The advantage of using a 2N3055 is it is available everywhere and is very cheap.

A disadvantage is that the gain is terribly low, and on top of that it varies widely from one device to the next. This means that that the resistance value must be determined for each transistor individually, and there is a good chance that the resistor will become fairly hot. If the 2N3055 is biased to dissipate 50 W and it has a DC gain (hFE) of 20, for example, the resistor will dissipate 2.5 W. The solution to this problem is to select a transistor with high hFE or use a Darlington pair.

Water Heater Construction
Drill four holes in the bottom of a water jug:
two for the fixing screws and two for the base and emitter leads. Fit a thin layer of silicone rubber (cut from a silicone baking cup or baking mould) between the mating surfaces of the transistor and the bottom of the water jug.

This material is suitable for use in contact with foods and beverages, and it can withstand temperatures up to nearly 200 degrees Celsius. The chromium of the 2N3055 package also appears to have no harmful effects on health, since immersion heaters are also chrome-plated.

Based on experience, the silicone rubber provides an adequately water-tight seal. Fit the bias resistor under the bottom of the jug, which will have to be fitted with small feet for this purpose. My 2N3055 heater has been working well for some time now, and I’m free of the problem of burnt-out immersion heaters. The silicon of the 2N3055 can obviously take the heat better than the material used to make the heater wires.

This principle can also be used for an aquarium heater or any other device where a liquid has to be heated to a certain temperature. In addition, you can use a temperature sensor to control the dissipation of the 2N3055 by regulating its base current and thus keep the liquid at a specific temperature. Author: J. G. Geradts (Netherlands)

This is a handy tip that can be put to a variety of uses. If you use a 2N3055 to heat drinking water or foods, be sure to use the chrome-plated version instead of the version with a matte metal package, which is also commonly available.

LED Volt Meter Circuit LM324

2009-07-26T20:07:00.000-07:00

It's a very useful circuit which when installed on your car gives the voltage of you car battery in a LED dot display form.The meter circuit is based on four comparators made of quad op amp LM324.

The inverting inputs of IC are kept at at reference voltages 5.6V,5.2V,4.8V,4.4V respectively at pins 2,6,9,13 by resistors ,R3,R4,R5,R6.The battery voltage is directly fed to the non inverting input through the voltage divider arrangement using R1 and R7.When there is variation in the input supply the out put of each op amp goes high accordingly as they are wired as voltage comparators.The corresponding LED glows.

LED Volt Meter Circuit Notes

IC LM 324 consists of4 op amps in one package , so power supply is common and is shown once (pin 4 and 11).
To setup , connect the circuit to battery ,adjust R6 so that required voltages are available at the inverting pins( refer description to get the required voltages).
Fix the LED’s on the dash board and mark the voltages near to it as shown in circuit diagram.The gadget is now ready.

Source: Car battery Volt meter circuit using LED

Decibel Audio Meter Circuit LM324

2009-07-26T19:56:00.000-07:00

This audio meter circuit below responds for sound pressure levels from about 60 - 70 dB (decibel). That sound is picked up by an 8 ohm speaker, amplified with a transistors stage and IC number LM324 op-amp section.

You can using also a dynamic microphone but I have found the speaker was more sensitive. The remaining three sections of the IC LM324 quad op-amp are used as volts comparators and drive three indicator LEDs or incandescents which are spaced about 3dB apart.

An additional transistor is needed for incandescent lights as shown with the lower lamp. I used 12 volt, 50mA lamps. Each light represents about a 3dB change in sound level so that when all 3 lights are on, the sound level is about 4 times greater than the level needed to light one lamp. The meter sensitivity can be adjusted with the 500K pot so that one lamp comes on with a reference sound level. The other two lamps will then indicate about a 2X and 4X increase in volume.

In operation, with no input, the DC voltage at pins 1,2 and 3 of the op-amp will be about 4 volts, and the voltage on the (+) inputs to the 3 comparators (pins 5,10,12) will be about a half volt less due to the 1N914 diode drop. The voltage on the (-) comparator inputs will be around 5.1 and 6.5 which is set by the 560 and 750 ohm resistors. When an audio signal is present, the 10uF capacitor connected to the diode will charge toward the peak audio level at the op-amp output at pin 1. As the volume increases, the DC voltage on the capacitor and also (+) comparator inputs will increase and the lamp will turn on when the (+) input goes above the (-) input.

As the audio volume decreases, the capacitor discharges through the parallel 100K resistor and the lamps go out. You can change the response time with a larger or smaller capacitor. This circuit requires a well filtered power source, it will respond to very small changes in supply voltage, so you probably will need a large filter capacitor connected directly to the 330 ohm resistor. I managed to get it to work with an unregulated wall transformer power source, but I had to use 4700uF. It worked well on a regulated supply with only 1000uF.

Source: Decibels Meter Circuit with LM324

Audio Level Meter Circuit LM3915

2009-07-26T19:44:00.000-07:00

This meter circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V.

The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs providing a logarithmic 3 dB/step analog display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The IC contains an adjustable voltage reference and an accurate ten-step voltage divider.

The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ?35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.

Source: Audio Level Meter

MM5314N Driven Digital Clock Circuit

2009-07-18T04:37:00.000-07:00

The circuit has been designed to create a digital clock using a single IC MM5314N with all the functions provided in the operation.

Terminology

MM5314 – a monolithic MOS integrated circuit that utilizes P-channel low threshold, enhancement mode and ion planted, depletion mode devices which has features such as internal multiplex oscillator, fast and slow set controls, single power supply, 7-segment outputs, leading zero blanking, operating at 50 Hz or 60 Hz, and 12 or 24 hour display format
7 Segment LED – is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays also known as seven-segment indicator

Digital Clock Circuit Explanation

A digital clock is a type of clock in which the time is displayed in a numerical form being associated with electronic devices. It uses a digital display rather than moving hands. The basis of the circuit design evolves in a single MOS IC MM5314N. Other necessary circuits are operated through the MM5314 IC which works together with six common anode 7-segment displays. The multisegment LED common anode configuration reduces the number of wires between the LED modules where all positive ends are connected together. In practical design, the longest pin of the LED is the positive or the anode part.

The 7-segment displays are driven by thirteen transistors consisting of BC550 and BC560. The timing of the circuit is determined by the frequency of the network with a value of 50 Hz, which imposes the simplest solution. To maintain a stable output frequency, a crystal oscillator may be used. It uses a quartz crystal to produce fixed frequency oscillations where accuracy and stability are the primary considerations. It uses the mechanical resonance of a vibrating crystal to produce a very precise frequency from the creation of an electrical signal.

The six displays of 7-segment common anode provide the output for the time. LEDs DS1 and DS2 represent the Hour, LEDs DS3 and DS4 represent the Minutes, and LEDs DS5 and DS6 represent the Seconds. The collector of transistors Q8 to Q13 powers the common anode of each display. Each display consists of individual LEDs a, b, c, d, e, f, & g, are linked in parallel combination, which are then driven by the transistors Q1 to Q7. This type of connection creates a multiplexing system with a frequency of 1 KHz that is controlled by the RC circuit R3 and C3. The power supply contains the typical circuit having a bridge rectifier across the secondary coil with a parallel capacitor across the bridge. The resistor R2 and capacitors C2 to C5 handles the separation and limiting of voltage to protect the integrated circuit from surge and peak voltages.

The rectified vibrations in pin 16 are limited by the diode D1 while resistors R18 to R24 are limiting the excess current from the LED. The use of switch S1, if put in position 1, is to adjust the clock to the required time and display. It will remain open unless it is switched to the other position which causes the display to be in a fixed value and save the settings, resuming the operation of the clock. In this scenario, the clock may be placed with a tolerable distance to avoid the effect of light from the LED display. Switch S2 on the other hand is responsible for adjusting the clock to operate on a 12-hour or 24-hour basis by changing the positions of the contacts. The adjustments of seconds are made possible when switch S3 is in position 1. The setting for the seconds is saved when the contact is changed to position 2. During an interruption in the operation of the clock, switches S3, S4, and S5 can be used for alterations. These are push-to-make switches which return to its normally open or OFF position upon releasing the button, like the standard doorbell switch.

The frequency of the main voltage around 50 Hz or 60 Hz is fed into pin 11 which is connected to pin 2 if the main voltage is 110 VAC at 60 Hz. Otherwise, pin 11 will not be connected anywhere if the main voltage is 220 VAC at 50 Hz. Pin 16 handles the incoming 50 Hz or 60 Hz at the input with the sample from the main voltage. The counter circuits are triggered by the sample function which becomes the adjustment of time. Having 110 V causes the pin 11 to connect Vss at pin 2 while having a 220 V nulls the function of pin 11.

Digital Clock Circuit Parts List
R1= 100Kohms
R2= 47Kohms
R3= 100Kohms
R4.....10= 2.2Kohms
R11.....17= 10Kohms
R18.....24-25-26= 220 ohms 0W5
R25-26=1.2Kohms 0W5 C1= 2200uF 25V
C2= 100uF 25V
C3= 18nF 100V polyester
C4-5= 10nF ceramic OR polyester
Q1....7= BC550
Q8....13= BC560
IC1= MM5314N D1= 1N4148
GR1= 4X1N4002
S1...3= 1X2 mini switch
S4...6= Push Button normal open
T1= 220V AC/12V 1A
DS1....DS7= 7 Seg. Disp. Common Anode

Digital Clock Circuit Application

Digital clocks are widely used as desk clocks, interval timers, industrial clocks, or automobile clocks. They can also be utilized in cell phones, computers, microwave ovens, televisions, and radios, since digital clocks are inexpensive and very small devices, which make them more popular in the designs. The LED digital clocks are also used as digital electronic time zone displays used in governments and companies with more than one office across the country or around the world. Schools, universities, and hospitals are using wireless clocks as the desired method for providing synchronized clocks without the need to lay sync wire.

Source: MM5314N Driven Digital Clock Circuit

Alarm Digital Clock-DS1307

2009-07-18T04:16:00.000-07:00

DS1307 is a hardware realtime clock, which works on I2C protocol. Better graphics using the same old fashioned alphanumeric LCD (type HD44780). Icons which shows the status for Alarm ON/OFF state, which gives a nice and cute look to the clock.

Circuit diagram for the digital clock. 2x16 LCD is connected to the port 2 of AT89C51. P1.0 of uC will provide the SCL (serial clock) and P1.1 SDA (serial data) for I2C communication.

There are four switches connected to the uC, as shown in the figure. Function of the keys are same as clear from their names.

When the power supply is switched on it will give you the default date and time, but later you can change it to the desired value. After setting once, the backup battery will keep the clock ticking even after the power is not there.

A little about I2C:
There are basically four main conditions in I2C protocol.

Start Condition-When SCL is high and SDA H->L, will be taken as start condition for the communication.
Stop Condition-When SCL is high and SDA L->H, will generate a stop condition.
Data Validity-When SCL is high there should be no chande in SDA line only then the data is valid, the data change should be made only when SCL is low.
Acknowledgement-After sending of one byte of data the reciever has to acknowledge the sender for the successful reception. for this the sender make the SDA line high and reciever pulls down the SDA low, which tells the sender that data has reached safely.

Now the source code written in assembly, basically implements the I2C protocol. the assembly source written for Keil. Download for Clock.asm and the Clock.hex file for programming the controller. Digital Clock Schematic is available in PDF format can be downloaded..

NOTE:
For ppl who wants to edit the code but they dont have the A51 Macro assembler/Keil, they can use the following software to disassemble the hex file and change it according to their need. The disassembling software can be downloaded from following link:
DIS8051 Cross-Disassembler V2.1 its a free 8051 disassembler for MS-DOS by Data Sync Engineering.

Reassembling can be done using any of the free softwares
Crimson Editor 3.45 R2, a free versatile editor by Ingyu Kang. or you can use
PseudoSam 8051 Cross Assembler, V1.4.09 (Recommended)

Source: Digital Clock with Alarm Using DS1307

Alarm Equipped Digital Clock LM5860

2009-07-18T03:56:00.000-07:00

The LM8560 is alarm equipped digital clock Integrated Circuit with built-in driver capable of directly driving LED display equipment. As Intehrated Circuit himself the VDD pin for the LM8560 is graded to withstand a voltage of 15V.

LM8560 digital clock circuit has many features like:

Single chip P-channel ED MOS LSI.
LED direct drive using time division (duplex configuration).
Wide operating power supply voltage range.
Built-in alarm function with 24-hour control.
Supports changeover between 12-hour AM/PM and 24-hour displays
Built-in battery backup CR oscillator.
Built-in automatic fast forward function for hour and minute settings.
Built-in sleep timer function (maximum intervals of 59 minutes or 1 hours and 59 minutes).
Built-in snooze function supporting repeat use.
Equipped with power failure display function.
900Hz output for alarm tone .

Using LM8560 circuit you will have many advantages , because of integration in one package of all features you can use it in small clock alarm radio circuits or in a simple clock alarm circuit. For LM 8560 clock alarm circuit you can use a positive or negative power supply maximum 15 volts.

Bench Power Supply Circuit

2009-07-18T03:21:00.000-07:00

Every electronics engineer is familiar with the anxiety of the moment when power is first applied to a newly-built circuit, wondering whether hours of work are about to be destroyed in a puff of smoke. A high quality power supply with an adjustable current limit function is an excellent aid to steadying the nerves.

Unfortunately power supplies with good regulation performance are expensive and homebrew construction is not always straightforward. Many of the "laboratory power supplies" currently on the market are low-cost units based on switching regulators which, although certainly capable of delivering high currents, have rather poor ripple performance. Large output capacitors (which, in the case of a fault, will discharge into your circuit) and voltage overshoot are other problems.

The power supply described here is a simple unit, easily constructed from standard components. It is only suitable for small loads but otherwise has all the characteristics of its bigger brethren. Between 18 V and 24 V is applied to the input, for example from a laptop power supply. This avoids the need for an expensive transformer and accompanying smoothing. No negative supply is needed, but the output voltage is nevertheless adjustable down to 0 V.

A difficulty in the design of power supplies with current limiting is the shunt resistor needed to measure the output current, normally connected to a differential amplifier. Frequently in simple designs the amplifier is not powered from a regulated supply, which can lead to an unstable current regulation loop. This circuit avoids the difficulty by using a low-cost fixed voltage regulator to supply the feedback circuit with a stable voltage. This arrangement greatly simplifies current measurement and regulation.

To generate this intermediate supply voltage we use an LM7815. Its output passes through R17, which measures the output current, to MOSFET T1 which is driven by the voltage regulation opamp IC1C. Here R11 and C4 determine the bandwidth of the control loop, preventing oscillation at high frequencies. R15 ensures that capacitive loads with low effective resistance do not make the control loop unstable. The negative feedback of AC components of the current via R12 and C5 makes the circuit reliable even with a large capacitor at its output, and negative feedback of the DC component is via the low-pass filter formed by R14 and C6. This ensures that the voltage drop across R15 is correctly compensated for. C7 at the output provides a low impedance source for high-frequency loads, and R16 provides for the discharge of C17 when the set voltage is reduced with no load attached.

Current regulation is carried out by IC1D. Again to ensure stability, the bandwidth of the feedback loop is restricted by R19 and C8. If the voltage dropped across R17 exceeds the value set by P2, the current limit function comes into action and T2 begins to conduct. This in turn reduces the input voltage to the voltage regulation circuit until the desired current is reached. R7, R9 and C3 ensure that current regulation does not lead to output voltage overshoots and that resonance does not occur with inductive loads.

The controls of the power supply are all voltage-based. This means, for example¸ that P1 and P2 can be replaced by digital to analogue converters or digital potentiometers so that the whole unit can be driven by a microcontroller. IC1B acts as a buffer to ensure that the dynamic characteristics of the circuit are not affected by the setting of P1.

IC1A is used as a comparator whose output is used to drive two LEDs that indicate whether the supply is in voltage regulation or current regulation mode. If D2 lights the supply is in constant voltage mode; if D1 lights it is in constant current mode, for example if the output has been short circuited. The power supply thus boasts all the features of a top-class bench supply. IC1A and its surrounding circuitry can be dispensed with if the mode indication is not wanted.

A type LM324 operational amplifier is suggested as, in contrast to many other similar devices, it operates reliably with input voltages down to 0 V. Other rail-to-rail opamps could equally well be used. The particular n-channel MOSFET devices used are not critical: a BUZ21, IRF540, IRF542 or 2SK1428 could be used for T1, for example, and a BS170 could be used in place of the 2N7002. The capacitors should all be rated for a voltage of 35 V or higher, and R15 and R17 must be at least 0.5 W types. The fixed voltage regulator and T1 must both be equipped with an adequate heatsink. If they are mounted on the same heatsink, they must be isolated from it as the tabs of the two devices are at different potentials.

Source: Mini Bench Power Supply Circuit

Digital Clock Circuit-CMOS 4047

2009-07-18T02:48:00.000-07:00

This circuit provides a digital square wave that can be viewed directly or used to drive other circuits. It used the CMOS 4047 Low-Power Monostable/Astable Multivibrator. As used in Tom Duncan's Adventures with Digital Electronic's Book, to drive CMOS Decade of 4-bit binary counters.

RC = 10M x 100nF = (10x106) x (100x10-9) = 1 Hz
OscOut (Double Frequency of Q)
_
Q (Inverse of Q)
Q (Square Wave, Frequency RC Hz, 1:1 Mark:Space Ratio)
These 3 outputs can be viewed using an LED and 330R Resitor in series

CMOS 4047 Low-power astable/monostable multivibrator with oscillator output.

Source: CMOS 4047 Digital Clock Circuit