Free Electronic Circuit

Stereo Parabolic Microphone

noreply@blogger.com (Quick Zone) — Thu, 24 Sep 2009 02:51:00 +0000

This circuit is a stereo amplifier for a high sensitivity stereo parabolic microphone that able to used for listening to distant sounds. Typical parabolic microphones are monophonic, this unit has a stereo audio path that helps produce more realistic sounding audio. The Big-E can be used with headphones or as an audio source for a stereo tape recorder or a PC sound card.

This circuit also works nicely as a remote stereo audio receiver for accompanying a video surveillance system. It is capable of operating on the end of a four wire shielded cable that is more than 100 feet long. For remote operation, a set of inexpensive amplified PC speakers can be connected to the outputs for monitoring the sound.

Specifications
Operating Voltage: 9-15V (9V Nominal) DC
Operating Current: 7ma at 9V DC

How Does It Work
The circuit consists of two identical audio channels and some basic power supply filtering components. Only the left channel will be described.

The mini condenser microphone converts sounds into an electrical signal. Resistor R1 provides bias for the condensor microphone's internal amplifier transistor. The 2N3906 PNP transistor acts as a low noise microphone input amplifier. The 10K gain potentiometer is used for adjusting the audio signal level. A stereo 10K audio taper pot can be used for adjusting both channels simultaneously, or individual 10K trimmers can be used for fixed gain applications. The preamp output signal is fed into the 1458 op-amp, which boosts the audio to a level that is sufficient for driving an 8-ohm headphone or a tape recorder input. The 1458 amplifier stage is fixed gain (10X) in the inverting configuration, it drives the headphone speakers.

Capacitor C9 provides DC isolation from the 1458 op-amp output, which sits at half of the supply voltage. Resistor R13 provides impedance protection for the op-amp output and reduces audio distortion when driving low impedance headphones.

DC bias for the 1458 op-amps is set at half of the supply voltage by the R16/R17 voltage divider. Capacitors C13 and C14 filter the DC power supply for the op-amp stage. The DC is further filtered for the input preamp transistors through resistor R15 and capacitor C11. Diode D1 and resistor R18 protect the circuit from reverse battery polarity.

Construction
The Big-E circuit can be assembled on a circuit board, or hand wired. The board should be installed in a metal box for shielding from unwanted hum. For surveillance applications, the condenser microphones can be mounted directly on the PC board or on the edge of the metal box. The volume control can be mounted on the edge of the box, two 3.5MM mono jacks were used for the microphone inputs, a 3.5MM stereo jack was used for the headphone output. The 9V battery was mounted inside of the box, power is switched via a switch on the 10K stereo potentiometer.

The parabolic microphone assembly was made from an old Chinese wok cooker lid. The microphones are mounted on a metal standoff that places them at the focal point of the parabolic reflector. Pre-formed computer microphones were used for the model shown. The optimal microphone position can be found by pointing the reflector at a distant audio source, then moving the microphones for the loudest sound. The circuit box was mounted on the back side of the wok lid, it was attached to a piec of 1/2" square aluminum tubing, which forms a handle.

Parabolic Microphone Use
Start with the volume turned down, point the Big-E at a remote sound source, then gradually turn the volume up until the sound is heard. Be careful not to hit the side of the parabolic dish when listening, loud sounds can result. Also, beware that a malicious friend can cause you pain in the ears by talking loudly at the parabolic mic. It is advisable to wear the headphones partially off of your ears while you get used to the operation of the device. The Big-E is great for listening to birds and distant thunderstorms. It is also possible to hear the rustling of leaves on the top of a distant tree during a breezy day. Close-in wind noise may overpower distant sounds.

Stereo Parabolic Microphone PCB
Printed Circuit Image
Component Placement Silkscreen

Source: The Big-E Stereo Parabolic Microphone

AC Power Supply-Low Voltage

noreply@blogger.com (Quick Zone) — Wed, 23 Sep 2009 03:57:00 +0000

Here's AC power supply circuit with low voltage output (step down transformer converter). Warning! This project involves the use of dangerous voltages. You must make sure all high-voltage (120 volt household power) conductors are safely insulated from accidental contact. No bare wires should be seen anywhere on the "primary" side of the transformer circuit. Be sure to solder all wire connections so that they're secure, and use real electrical tape (not duct tape, scotch tape, packing tape, or any other kind!) to insulate your soldered connections.

If you wish to enclose the transformer inside of a box, you may use an electrical "junction" box, obtained from a hardware store or electrical supply house. If the enclosure used is metal rather than plastic, a three-prong plug should be used, with the "ground" prong (the longest one on the plug) connected directly to the metal case for maximum safety.

Before plugging the plug into a wall socket, do a safety check with an ohmmeter. With the line switch in the "on" position, measure resistance between either plug prong and the transformer case. There should be infinite (maximum) resistance. If the meter registers continuity (some resistance value less than infinity), then you have a "short" between one of the power conductors and the case, which is dangerous!

Next, check the transformer windings themselves for continuity. With the line switch in the "on" position, there should be a small amount of resistance between the two plug prongs. When the switch is turned "off," the resistance indication should increase to infinity (open circuit -- no continuity). Measure resistance between pairs of wires on the secondary side. These secondary windings should register much lower resistances than the primary. Why is this?

Plug the cord into a wall socket and turn the switch on. You should be able to measure AC voltage at the secondary side of the transformer, between pairs of terminals. Between two of these terminals, you should measure about 12 volts. Between either of these two terminals and the third terminal, you should measure half that. This third wire is the "center-tap" wire of the secondary winding.

It would be advisable to keep this project assembled for use in powering other experiments shown in this book. From here on, I will designate this "low-voltage AC power supply" using this illustration:

Source: Transformer -- power supply

ATX Power Supply Connector-Pinouts Diagram

noreply@blogger.com (Quick Zone) — Wed, 23 Sep 2009 03:33:00 +0000

Here's a standard for ATX Power supply connectors dan ATX power supply pinouts. Standard power supplies turn the incoming 110V or 220V AC (Alternating Current) into various DC (Direct Current) voltages suitable for powering the computer's components.

Power supplies are quoted as having a certain power output specified in Watts, a standard power supply would typically be able to deliver around 350 Watts.

The more components (hard drives, CD/DVD drives, tape drives, ventilation fans, etc) you have in your PC the greater the power required from the power supply.

By using a PSU that delivers more power than required means it won't be running at full capacity, which can prolong life by reducing heat damage to the PSU's internal components during long periods of use.

Always replace a power supply with an equivalent or superior power output (Wattage).

There are 3 types of power supply in common use:

AT Power Supply - still in use in older PCs.
ATX Power Supply - commonly in use today.
ATX-2 Power Supply - recently new standard.

The voltages produced by AT/ATX/ATX-2 power supplies are:

+3.3 Volts DC (ATX/ATX-2)
+5 Volts DC (AT/ATX/ATX-2)
-5 Volts DC (AT/ATX/ATX-2)
+5 Volts DC Standby (ATX/ATX-2)
+12 Volts DC (AT/ATX/ATX-2)
-12 Volts DC (AT/ATX/ATX-2)

A power supply can be easily changed and are generally not expensive, so if one fails (which is far from uncommon) then replacement is usually the most economic solution.

ATX Power Supply Connectors Diagram

ATX Power Supply Pinouts Diagram

12V Inverter Circuit

noreply@blogger.com (Quick Zone) — Sat, 19 Sep 2009 22:59:00 +0000

This 12V inverter is very easy to build, cheap components that many electronics hobbyists may even already have. Though it is possible to build a more powerful circuit, the complexity caused by the very heavy currents to be handled on the low-voltage side leads to circuits.

The circuit diagram of 12v inverter is easy to follow. A classic 555 timer chip, identified as IC1, is configured as an astable multivibrator at a frequency close to 100 Hz, which can be adjusted accurately by means of potentiometer P1. It is used to drive a D type flip-flop produced using a CMOS type 4013 IC. This produces perfect complementary squarewave signals (in antiphase) on its Q and Q outputs suitable for driving
the output power transistors.

As the output current available from the CMOS 4013 is very small, Darlington power transistors are used to arrive at the necessary output current. We have chosen MJ3001s from the now defunct Motorola (only as a semi-conductor manufacturer, of course!) which are cheap and readily available, but any equivalent powerDarlington could be used.

These drive a 230 V to 2 × 9 V centre tapped transformer used ‘backwards’ to produce the 230 V output. The presence of the 230 VAC voltage is indicated by a neon light, while a VDR (voltage dependent resistor) type S10K250 or S07K250 clips off the spikes and surges that may appear at the transistor switching points.

12 Inverter Parts List
Resistors
R1 = 18kΩ
R2 = 3kΩ3
R3 = 1kΩ
R4,R5 = 1kΩ5
R6 = VDR S10K250 (or S07K250)
P1 = 100 kΩ potentiometer
Capacitors
C1 = 330nF
C2 = 1000 μF 25V
Semiconductor
T1,T2 = MJ3001
IC1 = 555
IC2 = 4013
Miscellaneous
LA1 = neon light 230 V
F1 = fuse, 5A
TR1 = mains transformer, 2x9V 40VA (see text)
4 solder pins
PCB,

The Darlington transistors should be fitted onto a finned anodized aluminium heat-sink using the standard insulating accessories of mica washers and shouldered washers, as their collectors are connected to the metal cans and would otherwise be short-circuited.

An output power of 30 VA implies a current consumption of the order of 3 A from the 12 V battery at the ‘primary side’. So the wires connecting the collectors of the MJ3001s [1] T1 and T2 to the transformer primary, the emitters of T1 and T2 to the battery negative terminal, and the battery positive terminal to the transformer primary will need to have a minimum crosssectional area of 2 mm2 so as to minimize
voltage drop. The transformer can be any 230 V to 2 × 9 V type, with an E/I iron core or toroidal, rated at around 40 VA.

Properly constructed on the board shown here, the 12 inverter circuit should work at once, the only adjustment being to set the output to a frequency of 50 Hz with P1.

The circuit should not be too difficult to adapt to other mains voltages or frequencies, for example 110 V, 115 V or 127 V, 60 Hz. The AC voltage requires a transformer with a different primary voltage (which here becomes the secondary), and the frequency, some adjusting of P1 and possibly minor changes to the values of timing components R1 and C1 on the 555. Author: B. Broussas

Audio Power Meter Using Duo LED

noreply@blogger.com (Quick Zone) — Sat, 19 Sep 2009 22:13:00 +0000

Audio Power Meter indicates the amount of power that goes to a loudspeaker. This simple audio power meter circuit uses dual-colour LED that shows green at an applied power level of about 1 watt. At 1.5 watts it glows orange and above 3 watts it is bright red.

The audio power meter circuit is connected in parallel with the loudspeaker connections and is powered from the audio signal. The additional load that this represents is 470 Ohm (R1//R3) will not be a problem for any amplifier.

How The Audio Power Meter Works
During the positive half cycle of the output signal the green LED in the dual-colour LED will be turned on, provided the voltage is sufficiently high. At higher output voltages, T1 (depending on the voltage divider R2/R1) will begin to conduct and the green LED will go out.

During the negative half cycle the red LED is driven via R3 and will turn on when the voltage is high enough. In the transition region (where T1 conducts more and more and ‘throttles’ the green LED as a result) the combination of red/green gives the orange colour of the dual-LED.

By choosing appropriate values for the resistors the power levels can be adjusted to suit. The values selected here are for typical living room use. You will be surprised at how loud you have to turn your amplifier up before you get the LEDs to go!

The resistors can be 0.25 W types, provided the amplifier does not deliver more than 40 W continuously. Above this power the transistor will not be that happy either, so watch out for that too. Because T1 is used in saturation, the gain (Hfe) is not at all important and any similar type can be used. The power levels mentioned
are valid for 4-Ohm speakers. For 8-Ohm speakers all the resistor values have to be divided by two. Author: Michiel Ter Burg

Analog Milliamp Meter Used as Voltmeter

noreply@blogger.com (Quick Zone) — Tue, 30 Jun 2009 01:32:00 +0000

A milliamp meter can be used as a volt meter by adding a series resistance. 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 resistnace 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.

The milliamp meter can also be used to measure higher currents by adding a parallel resistance. 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

Car Anti-Theft Wireless Alarm

noreply@blogger.com (Quick Zone) — Thu, 20 Nov 2008 16:52:00 +0000

This alarm circuit is an anti- theft wireless alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF FM radio-controlled, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park.

The receiver unit of the wireless alarm uses an CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside. Receiver is tuned to the transmitter's frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transis- tor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energised.

When an intruder tries to drive the car and takes it a few metres away from the car porch, the radio link betw- een the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hissing noise. Hissing AC signals are coupled to relay switching circ- uit via audio transformer. These AC signals are rectified and filtered by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2. Thus transistor T2 conducts, and it pulls the base of relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on.

If, by chance, the intruder finds out about the wireless alarm and disconnects the transmitter from battery, still remote alarm remains activated because in the absence of signal, the receiver continues to produce hissing noise at its output. So the burglar alarm is fool-proof and highly reliable. (Ed: You may have some problem catching the thief, though, if he decides to run away with your vehicle_in spite of the alarm!)

Go to Car Anti-Theft Wireless Alarm Forum

Battery Low Voltage Beeper

noreply@blogger.com (Quick Zone) — Mon, 17 Nov 2008 12:46:00 +0000

This electronic circuit is an alarm circuit for low battery condition. It provides an audible and visual low voltage warning for 12V battery powered devices. When the battery voltage is above the set point (typically 11V), the circuit is idle. If the battery voltage should fall below the set point, the LED will light and the speaker will emit a periodic beeping sound to warn of the impending loss of power. The circuit was designed for monitoring solar systems, but it could also be useful for automotive and other 12V applications.

Parts Lists : Printed Circuit Image (PostScript File) Component Placement Silkscreen (PostScript File)

How it works
U2 provides a 5V regulated voltage reference. U1 is wired as a comparator, it compares the fixed 5V regulated voltage to the voltage on the wiper of VR1, that is proportional to the 12V supply. When the supply drops below the set point, the output of U1 goes low, turning on Q1 and powering the beeper and the LED.

The beeper consists of U4, a tone generator, and U3, a low duty cycle pulse generator. The tone can be changed by adjusting R7, the beep rate can be changed by adjusting R5. A small amount of hysteresis is provided by R1 and the current through LED1 and the beeper, this separates the on and off points for the circuit.

U2 provides a 5V regulated voltage reference. U1 is wired as a comparator, it compares the fixed 5V regulated voltage to the voltage on the wiper of VR1, that is proportional to the 12V supply. When the supply drops below the set point, the output of U1 goes low, turning on Q1 and powering the beeper and the LED.

The beeper consists of U4, a tone generator, and U3, a low duty cycle pulse generator. The tone can be changed by adjusting R7, the beep rate can be changed by adjusting R5. A small amount of hysteresis is provided by R1 and the current through LED1 and the beeper, this separates the on and off points for the circuit.

Use of Battery Low Voltage Beeper
Connect the circuit to the 12V source that you wish to monitor. Turn S1 on, if the battery voltage is above the set point, nothing should happen.

As the battery voltage drops below the set point, the LED will light and a periodic beeping will come from the speaker. If the beeping becomes annoying, turn off S1. Be sure to charge the battery soon, excessive discharging will shorten the life of most rechargeable batteries.

More about Battery Low Voltage Beeper

2-25V 5A Power Supply LM338

noreply@blogger.com (Quick Zone) — Fri, 14 Nov 2008 13:57:00 +0000

This power supply circuit uses a LM338 adjustable 3 terminal regulator to supply a current of up to 5A over a variable output voltage of 2V to 25V DC. It will come in handy to power up many electronic circuits when you are assembling or building any electronic devices. The schematic and parts list are designed for a power supply input of 240VAC. Change the ratings of the components if 110V AC power supply input is required.

The mains input is applied to the circuit through fuse F1. The fuse will blow if a current greater than 8A is applied to the system. Varistor V1 is used to clamp down any surge of voltage from the mains to protect the components from breakdown. Transformer T1 is used to step down the incoming voltage to 24V AC where it is rectified by the four diodes D1, D2, D3 and D4. Electrolytic capacitor E1 is used to smoothen the ripple of the rectified DC voltage.

Power supply parts list:

Diodes D5 and D6 are used as a protection devices to prevent capacitors E2 and E3 from discharging through low current points into the regulator. Capacitor C1 is used to bypass high frequency component from the circuit. Ensure that a large heat sink is mounted to LM338 to transfer the heat generated to the atmosphere.

More about 2-25V 5A Power Supply LM338

ICL7107 Digital LED Voltmeter

noreply@blogger.com (Quick Zone) — Wed, 12 Nov 2008 05:51:00 +0000

This circuit is a digital voltmeter with LED display. It's ideal to use for measuring the output voltage of your DC power supply. It includes a 3.5-digit LED display with a negative voltage indicator. It measures DC voltages from 0 to 199.9V with a resolution of 0.1V. The voltmeter is based on single ICL7107 chip and may be fitted on a small 3cm x 7cm printed circuit board. The circuit should be supplied with a 5V voltage supply and consumes only around 25mA.

The use of 7805 5V voltage regulator is highly recommended to prevent the damage of ICL7107, 555 ICs and to extend the operating voltages.

Parts list of The Digital LED Voltmeter:

R1 = 8K2 R1 = 8K2
R2 = 47K / 470K R2 = 47k / 470K
R3 = 100K R3 = 100K
R4 = 2K R4 = 2K
R5, R6 = 47K R5, R6 = 47k
R7 = 0R / 4K7 R7 = 0R / 4K7
R8 = 560R R8 = 560R
C1,C5, C6, C8, C9 = 100n C1, C5, C6, C8, C9 = 100n
C2 = 470n / 47n C2 = 470n / 47n
C3 = 220n C3 = 220n
C4 = 100p C4 = 100p
C7 = 10-22u C7 = 10-22U
D1, D2 = 1N4148 D1, D2 = 1N4148
IC1 = ICL7107 IC1 = ICL7107
IC2 = NE555 IC2 = NE555
OPTO = CA 10 pin FTA = CA 10 pin

The digital LED voltmeter can also be configured to measure different voltage ranges and display higher voltage resolution.

More about Universal Digital LED Voltmeter

5A Power Supply 1.2-25V

noreply@blogger.com (Quick Zone) — Tue, 11 Nov 2008 18:56:00 +0000

The core of the power supply circuit is LM338K. The scheme circuit 5A power supply with adjustable output voltage from 1.2 to 25V. Construction circuit is compact, all elements except transformer, the printed circuit. Serial element to the cooling body mounted over the aluminum-angular profile. One side of angular profile, therefore, lies between the printed circuit boards and regulators LM338K, the other side is mounted on cooling the body with one flat surface.

The regulator must be electrically isolated from the angular profile for better heat conductivity .Relationship with wires, the minimum and facilitated by the buckle on the printed circuit. Potentiometer to change the output voltage can be trimer potentiometer on a printed circuit or potentiometer on the front panel housing, with two wires connected to the printed circuit boards.

Manufacture power supply is simple and cheap.Constructed power supply is also suitable as a power supply for the benches as an experienced electrician, as well as the newcomer.

More info 5A Power Supply 1.2-25V

Power Supply Circuit 12-15 Volt 20A

noreply@blogger.com (Quick Zone) — Tue, 11 Nov 2008 18:37:00 +0000

Output voltage of the power supply circuit is adjustable from fine potensiometer from 12V to 15v. It is suitable for all 12V power supply devices, or devices which are normally connected to a 12V battery or a vehicle with a 12V power supply system. This tension is usually 13.8 V.

For above reason, The Power Supply is also set to this tension, all right, however, any voltage from 12V to 14V. In this case, the tension is set somewhere around 13.6 V. To provide tension resistance in addition to voltage regulator 78S12. Instead potentiometer 100R inserted resistor 56R.

The scheme of the power supply is simple, but it is partly taken from some of the schemes taken up in the past. The material used is easily obtainable in electronic component shops, and this was the condition when I started to design this power supply.

More about Power Supply Circuit

3A Regulated Power Supply 1-27 Volt

noreply@blogger.com (Quick Zone) — Tue, 11 Nov 2008 17:51:00 +0000

In circuit presented below, is used very few elements, power supply and will therefore be easy to manufacture. Serial power transistor will be as well known and popular 2N3055, but the power supply voltage and current regulation. Source voltage is 24V AC transformer.

Output voltage is adjustable with potensiometer P2 (10K), current limit is adjustable with P1 (500 ohm, 470 ohm can be). Current restrictions on the use of R5 resistance (0.15 ohm) in the value of the current maximum output of around 3.5 Ampere. Resistor R5 is 2.5 Ampere output current 0.22 ohm, for greater output current, the resistance R5 lower. For a good start would be to draw up a power supply from 0.22 ohm, then trying to find an appropriate maximum output current by changing the resistors.

An output power of the simple, it is used only one output transistor. Scene exit 723 is made with the PNP transistors Q1 medium power, the proposed BD712 or BD912, but will instead proposed fine also like transistors, which passed at least 2 Ampere flow and have allowed disipacijo at least 20W and a maximum voltage of at least 40 Volt. Outlet power transistor Q2 is 2N3055 or stronger.

In order to facilitate the assembly of the output transistors Q2 2N3055, which is in TO3 housing, I prepared a special template in the form of printed circuit boards.

More detail 3A Regulated Power Supply 1-27 Volt

Fan Controller with an LM76 as Temperature Estimator

noreply@blogger.com (Quick Zone) — Mon, 06 Oct 2008 09:06:00 +0000

This temperature sensor circuit is to control a small fan controller. An LM76 as temperature 'estimator' used in this project. To make it a little more interesting, an LPH7653 display to show the heat sink temperature and fan status.

This projects used an AT90S8535, but as the schematic shows, a lot of the controllers pins are left unused. You may want to select a smaller AVR. The choice will mainly be determined by the amount of program memory needed.

The use of the LM76 and the LPH7653 display is explained in the I2C chapter . Again, the MAX232 is used only to generate the (negative) display contrast voltage. The fan is switched with an N-channel Fet. Use a logic-level Fet that can handle the fan starting current and that has a low Rds-on, otherwise it might get hot!
The display shows the temperature in large format digits. When the fan is switched on, the display shows a slowly rotating fan:

The program source should explain how things work...

Source

Ultrasonic Pest Repellant

noreply@blogger.com (Quick Zone) — Wed, 01 Oct 2008 02:53:00 +0000

This electronic circuit is an ultrasonic pest repellant are repelled by variabble ultrasonic frequency in the range of 30 kHz to 50 kHz. Thus to increase the effectiveness, frequency of ultrasonic oscillator has to be continuously varied between certain limits.

By using this circuit design, frequency of emission of ultrasonic sound is continuously varied step-by-step automatically. Here five steps of variation are used but the same can be extended up to 10 steps, if desired. For each clock pulse output from op-amp IC1 CA3130 (which is wired here as a low-frequency square wave oscillator), the logic 1 output of IC2 CD4017 (which is a well-known decade counter) shifts from Q0 to Q4 (or Q0 to Q9).

Five presets VR2 through VR6 (one each connected at Q0 to Q4 output pins) are set for different values and connected to pin 7 of IC3 (NE555) electronically. VR1 is used to change clock pulse rate. IC3 is wired as an astable multivibrator operating at a frequency of nearly 80 kHz. Its output is not symmetrical. IC4 is CD4013, a D-type flip-flop which delivers symmetrical 40kHz signals at its Q and Q outputs which are amplified in push-pull mode by transistors T1, T2, T3 and T4 to drive a low-cost, high-frequency piezo tweeter.

For frequency adjustments, you may use an oscilloscope. It can be done by trial and error also if you do not have an oscilloscope. This pest repeller would prove to be much more effective than those published earlier because here ultrasonic frequency is automatically changed to cover different pests and the power output is also sufficiently high. If you want low-power output in 30-50 kHz ultrasonic frequency range then the crystal transducer may be directly connected across Q and Q outputs of IC4 (transistor amplifier is not necessary).

Source: http://www.radioland.net.ua/electronic-circuit-id-29.html

Mosquito Repellant Circuit with BC547

noreply@blogger.com (Quick Zone) — Wed, 01 Oct 2008 02:36:00 +0000

This Moosquito repellat circuit uses two BC547 transnistor as astable multibibrator. The Astable Multivibrator, which is generally used as a signal generator, is once again used here to generate the desired frequencies. It is an excellent example of the fact, how versatile simple basic electronic circuit can be.

Astable Multivibrator Circuit Operation
When T1 is conducting T2 is off and when T2 is conducting, T1 is off. The capacitors C1 and C2 contributes decisively to this ON/OFF cycles for the transistors T1 and T2. The time taken by C1 and C2 to charge and discharge decides the shape of the output waveform. Another important factor in the operation of the circuit is the fact that the transistor goes into conduction only when the base-emitter voltage exceeds 0.7 volts (for silicon transistors). From this basic knowledge we can visualise how the transistors exchange their roles and how the voltage on the collector of each transistor jumbs between the lower and upper level, producing a rectangular waveform. If you take a close look at circuit, you will notice that C1 and C2 are not equal. They differ in their values by a factor of four.

The output signal will thus be a non symmetrical waveform. Such a non symmetrical signal contains more high frequency harminics compered to the normal square wave signal. The output of our circuit will have the basic frequency of 5 KHz along with harminics of 10, 15 and 20 KHz. If some insects are deaf to frequencies upto 5 KHz, they may react to 10 KHz or 15 KHz or even 20 KHz, one never knows ...

The piezo buzzer used should not have an internal oscillator built into it. The circuit consumes 0.3 ma current, and can give about 1500 hours of nonstop operation.

Parts List:
R1,R4 - 10 K Ohm
R2,R3 - 560 K Ohm
C1 - 82 PF
C2 - 330 PF
T1,T2 - BC547
Piezo Buzzer (Without internal oscillator)

Source: http://www.flashwebhost.com/circuit/mosquito.php

Insect Repellant with CMOS 4047

noreply@blogger.com (Quick Zone) — Wed, 01 Oct 2008 02:29:00 +0000

This elctronic circuit is an insect repellant using IC CMOS 4047. Repell those repugnent insects from your Garden this Summer with this insect repellant circuit.

This insect repellant circuit designed by Graham Maynard the circuitry consists of a phase locked loop (CMOS 4047) wired as a 22KHz oscillator. The output is amplified by a pair of complimentary output transistors and drives a Motorola 3.25 inch Piezo. Current drain is around 120mA so an external power supply is recommended.

The piezo used was a standard 85mm square Motorola Horn, Maplin part number WF09K or WF55K. These are rated +/-3dB to 28kHz.

Source: http://www.mitedu.freeserve.co.uk/Circuits/Misc/insecrep.html

Three in One Tester for Audio, Diode, and Circuit

noreply@blogger.com (Quick Zone) — Fri, 26 Sep 2008 19:33:00 +0000

This electronic schematic circuit is a test circuit for audio, diode and circuit. This very handy simple solid state battery operated tester. It works on two 1.2-1.5 AA-batteries.

This three in one tester can be used for :

audit AF/LF signal
circuit tester
diode tester
1 KHz tone generator

When you switch S1 OFF the diode/circuit testerschematic can be used.

Source: http://users.belgacom.net/hamradio/homebrew.htm

Making Really Good Homemade Printed Circuits Boards (PCBs)

noreply@blogger.com (Quick Zone) — Sat, 20 Sep 2008 18:34:00 +0000

Want to know how to make really really good homemade Printed circuit boards? This taken is from original posting of Mike's Electronic Stuff. This page contains a guide to producing consistently high quality PCBs quickly and efficiently, particularly for professional prototyping of production boards. Unlike most other PCB homebrew guides, emphasis is placed on quality, speed and repeatability rather than minimum materials cost, although the time saved by getting good PCBs every time usually saves money in the long run - even for the hobbyist, the cost of ruined PCB laminates can soon mount up!

With the methods described, you can produce repeatably good single and double-sided PCBs for through-hole and surface mount designs with track densities of 40-50 tracks per inch and 0.5mm SMD pitches.

This information has been condensed from over 20 years' experience of making PCBs, mostly as prototypes of boards to be put into production. If you follow the methods outlined here exactly, you WILL get excellent quality PCBs every time. By all means experiment, but remember that cutting corners can easily reduce quality & waste time.

I will only consider photographic methods in depth - other methods such as transfers, plotting on copper and the various 'iron-on' toner transfer systems are not really suited for fast, repeatable use. Although I've heard some good reports from some toner transfer systems, the problem with these is that the 'expensive part' is the film, and you can't really feed much less than an A5 sheet through a laser printer, so you waste a lot on small PCBs. With photoresist laminate and cheap transparency media, you only use as much of the expensive part (the board) as you need, and offcuts can usually be used later for smaller boards. Double-sided PCBs are also rather tricky with toner-transfer methods.

Source: Mike's Electric Stuff

Oxygen Sensor Simulator

noreply@blogger.com (Quick Zone) — Sun, 13 Jul 2008 22:58:00 +0000

This electronic circuit is an oxygen sensor simulator that 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.
Source

UHF TV RF amplifier 5W

noreply@blogger.com (Quick Zone) — Sat, 12 Jul 2008 07:59:00 +0000

This electronic circuit is a RF Power Amplifier for driving small UHF TV transmitters. Its gain is 7dB and can amplify a signal between 450-800 MHz. You can drive the circuit with 1 to 1,5 Watts signal. Better use double layer PCB with the second layer connected to earth. Use a stabilized power supply 25 volts and at least 5Amps.

The transistor case is the SOT-122A and be careful because the transistor is very toxic for your health. Tuning can be achieved turning the two variable capacitors. Do not forget to use heat sink for both transistors, specially for the BLW89 and it would be better if you place a small fan as well.

Source: http://www.next.gr/inside-circuits/5-watt-uhf-tv-linear-amplifier-l4899.html

Telephone Hybrid Circuit

noreply@blogger.com (Quick Zone) — Sat, 12 Jul 2008 06:28:00 +0000

This electronic circuit is a telephone hybrid. It is intended to be used to create an easy connection beetween telephone line and studio equipment. Connect the two wires of the telephone line to the tip and ground of the line input and connect the telephone itself to the phone output on the tip and ground only.

Now the hybrid is interfaced (fully balanced) between your telephone and its connection to the outside world. The hybrid is now capable of splitting the send and return signals. Connect the hybrid balanced audio input to a (preferabie) balanced output of around +4dBu. This output has to be the mix of all signals except the signal coming from the hybrid itself to avoid feedback. An Aux. output will do, or in broadcast mixers a modified cleanfeed is the best.

RF Dual DC Motors Controller

noreply@blogger.com (Quick Zone) — Tue, 03 Jun 2008 16:26:00 +0000

The transmitter circuit consists of WZ-X01 RF module, Holtek HT-640 encoder and 8 bit A/D converter. U1 ADC0804 converts the analog voltage to digital data, U2 encodes that data (D0~D6) along with D6, D7 and transmitting through the RF transmitter module.

The potentiometer VR1 varies the voltage to the A/D U1 pin6, since only the lower 6 bits are used; the trim pot VR2 has to adjust so that the maximum input to the U1 will not exceed 1.25V. The S2 (D6) and S3 (D7) are used for controlling the rotation direction of the motors. S1 set the transmitter address; this address has to match with the address of the decoder circuit.

The receiver module WZ-R01 receives the data from the transmitter and feeds that data to the decoder U1 (HT-648L); the 8bit data will then be decoded. The first two significant bits D7 and D6 control the motor rotation direction. The lower 6 bits vary the duty cycle of the output pulse. U2 is a 12bit counter; it is configured so that it will reset itself every 64 counts. The oscillation circuit forms by U4c, U4d and U4e providing approximately 1MHz clock to the counter U2.

The 8-bit magnitude comparator U3 (74HCT688) compares the data from the counter U2 with the data of the decoder U1; when data from both are match, it will output a pulse to cause the D-flip flop U5 changing it's state.

By varying the data output of the decoder from 0-64; the duty cycle of the output pulse at U5 pin5 can also change from 0-100%. This output pulse will then be used to control the speed of the motor.

With 1MHz clock input the PWM frequency output is about 15.6KHz. The motor has less audible noise when run at a frequency higher than 10KHz.You may need to change the frequency depending on the motor you're going to use.

The motor driver section is very straightforward; the LMD18200 can handle 3A continuous motor current and 6A peak. In this circuit the sign/magnitude mode of operation is implemented. The current sensing circuit provides protection to both the driver and the motor; it set at 2A max. You can change the current limit by using a different current sensing resistor value (see LMD18200 data sheet for details) or the voltage reference at pin6 of the U7Op-Amp

All of the components use in this project can be purchased from us. Email us at wzmicro@worldnet.att.net, if you have any questions or comments. Your feedback is mostly appreciated.

Telemetry Transmitter for Small Animal

noreply@blogger.com (Quick Zone) — Tue, 03 Jun 2008 16:16:00 +0000

The goal of this project was to build a small, cheap, light-weight telemetry transmitter to attach to a small animal. This version uses a commercial, low-power transmitter, the Radiotronix RCT-433-AS. The design worked well, but has a relatively high current draw of about 500 microamps. A CR1620 lithium coin cell runs the circuit for about a week. The current version uses a pair of CMOS oscillators to produce a chirp once per second.

The circuit shown above has two standard CMOS multivibrators. The second is gated by the first. The duty cycle of the first oscillator is about 1%, or 10 mSec every second. A logic-high at the telemetry transmitter control turns it on.

The circuit board was layed out using ExpressPCB software. You will need to download a copy to view the design file. The components are all surface mount. The dots shown below are on a 0.1 inch grid.

Note the antenna lead at the lower left. At 433 MHz (70 cm wavelength) a quaterwave antenna should be 17 cm long. The battery is partly shown at the right. It is a CR1620 lithium cell, but any 3 volt source may be used. The transmitter module sticks out to the left. Visit page

River Level Monitoring System - RiverSpy2 #2

noreply@blogger.com (Quick Zone) — Tue, 03 Jun 2008 16:01:00 +0000

How to get started
As you can see from the picture at part #1, the original system was prototyped using veroboard. If you are not familiar with electronics, you will find it easier to build using a printed circuit board (pcb). The layout files are given below. You can order from within the expresspcb program. The MiniBoard service at expresspcb costs US$83 for 3 boards, including a courier service to Ireland. You only need one pcb per gauge but it is not possible to order just one pcb. (If you have a spare pcb, please send it to Daithi Power, Electrical Engineering Dept, University College Cork, Ireland) Alternatively, if you have pcb making facilities of your own, use the express pcb software to print overlays and make a pcb yourself. The right hand side of the pcb snaps off to make the sensor board. The larger left side is used to make the controller board. The controller board measures 3" by 2.5". The sensor part is 0.8" by 2.5".

To assemble and test the circuit, you will need the following tools

* Soldering iron, solder and a small wet sponge to clean the iron
* A small pliers and a snips
* Multimeter for measuring voltages and testing connections

Electrical schematic is here

Bill of materials is here

PCB silkscreen is here

PCB layout is here View and order PCBs using the free software at www.expresspcb.com Three mini-boards cost $51 + shipping.

Assembly drawing of the layout

Sensor
Start with the pressure sensor end. Its the section in the dashed box on the first page of the schematic. Pictures of the construction are shown here. You will need a soldering iron, fine solder, a piece of vero board, a snips and a volt meter. Order the pressure sensor (26PCBFA6D), the INA122, and a small aluminium box from farnell. You will also need a 4m length of 1/4" plastic tubing and a long length of 3 core cable. The length of cable depends on the distance from the sensor to the solar panel at the river bank. Measure the distance with a throw-bag rope and add a few metres. I used shielded cable but ordanary house wiring cable should do fine. Solder the circuit together, power it with a 9V or 12V battery and measure the output using a volt meter. It should read about 0.1V normally and increase when you suck on the tube. If all is ok, put it in the box. You will have to drill holes in the box for the tube and cable. Use a separator to create a cavity for the open end of the sensor as shown in the pictures. Test the circuit again an d then fill it with epoxy. Make sure nothing is shorted to the side and that epoxy doesn't get into the open end of the sensor. Test it again while the epoxy is wet by connecting a battery to the far end of the cable. If something has shorted, you will still have a chance to move things around. If all is ok, stick on the lid and let it dry. After it has cured, drop it in a barrel of water and power up the far side of the cable with your battery. If the signal voltage reads somewhere around 1.5V per metre of water, pat yourself on the back.

Before I potted the sensor with epoxy, I screwed the box to one end of a 0.5m length of stainless steel. At the other end of the steel, I drilled some 10m holes to allow me to bolt the sensor to the side of an existing stick gauge at the river bank. The distance between the sensor and 10mm holes allowed the sensor to be mounted under the water without having to drill any holes under water. The system should be installed while the river is at a very low level to ensure the sensor always stays under water.

Pictures of sensor construction
Datasheets for the components can be found at Honeywell , Texas Instruments and Farnell

Controller
Order the controller components and solder them in. The PIC, PT6102 and the INA122 can be obtained as free samples. Look at the Bill of Materials to get order numbers for the rest of the components. Use an ic socket to mount the PIC. The Batt and Phone connectors have extra holes to either use terminal blocks or "Molex" connectors. I find Molex very convenient but if you don't have a crimping tool, go for the terminal blocks. Once assembled you will need access to a PIC programmer such as the ICD2. If you have no way of prorgamming it, send me a PIC and I'll program it for you. Program the PIC using the hex file below and the MPLAB softwar e that you can download from Microchip. During programming, the ICD2 needs to be connected to, and configured to use, an external 9V supply. If you're stuck, send me a PIC and I'll program it for you. Next power up the system using a 12V supply or a battery. The LED should toggle on and off every second.

Hex file for programming PIC is here

Phone

So far, I have built systems using the Siemens M35 and the C45. Any old Siemens phone should do but the connectors on the later ones have gotten smaller so it won't be as easy to solder on the wires. The battery is removed from the phone and it is powered directly by the controller. The AT language used to talk to the internal modem is much the same for all Siemens phones. I have put some pictures of wiring an M35 here . The wire needs to be very fine. I used "wire-wrap" wire. It helps to put some solder on the wire before soldering to the phone. In the pictures shown, the red and black wires are soldered directly to the phone pcb. It is also possible (and easier) to solder them to the contacts that would normally press against the battery. Siemens also make a range of GSM modems such as the TC35. These are made for telemetry applications and would be easy to wire up but would cost you a lot more that an old phone.

Phone connector pin-out here

Pictures of phone wiring here

Installation
A picture of an early RiverSpy rev 2.0 controller is shown below. The latest version is a bit larger and uses through hold components instead of surface mount to make it easier for an inexperienced person to assemble. I'll put up some pictures of the latest rev later.

Terminal block for solar panel or external 12V supply
Molex connector for battery (paralleled with connector 1)
Debugging interface can be used to monitor phone communications using a pc serial port
ICD2 interface for programming the PIC
Molex connector to mobile phone
Molex connector to underwater sensor

The controller, battery and phone should be mounted in a waterproof box. A plastic box allows optimum phone coverage but if vandalism concerns require the use of a metal box, then an external antenna for the phone may be required. A frame should be contructed to mount the solar panel and the box. To optimise solar energy in winter, the solar panel must face south, have a clear view of the sky and be inclined at 70 degrees to the horizontal. Once all of the components have been connected together, configure it as per the installation manual given below.
Send me an email if you need some help.

Installation manual is here

Debugging

I have also put up a schematic of a small circuit that I use for debugging here. All it does is convert a 5V-0V signal to a +12V-12V signal suitable for connecting to the serial port of a pc or laptop. It listens in on the communications between the control board and the phone. I normally connect it to the RX (receive) line of the PIC. RX and GND are at pins 5 and 6 of the connector J4. RX carries the data going from the phone to the PIC. The phone should echo the characters sent from the PIC to the phone so you should see both sides of the conversation. If this is not working, it can also be connected to the TX (transmit) line but this only shows the characters sent by the PIC. The characters can be displayed on the pc using hyperterminal set at COM1, 9600,N,8,1, no flow control. A similar circuit is included in a siemens pc data cable so if you have one of those, just disassemble the connector at the phone end and use that instead. The pinout of the phone connector is given here. Do not connect the TX of the data cable (pin6, RX of the phone) to the phone at the same time as connecting the TX from the PIC. (its like two people trying to talk using walkie talkies at the same time) Also note that pin 3 (Power) and pin 4 (Fbatt+) shown in the phone connector pinout are not the same as the positive terminal of the phone battery (BATT+).

Contacts
If you have questions, contact Daithí Power, visit page