Thursday, February 27, 2014

MP3 FM Transmitter Circuit Diagram

Heres a simple VHF FM transmitter that could be used to play audio files from an MP3 player or computer on a standard VHF FM radio. The circuit use no coils that have to be wound. This FM transmitter can be used to listen to your own music throughout your home. When this FM transmitter used in the car, there is no need for a separate input to the car stereo to play back the music files from your MP3 player.

Project image :
MP3-FM-Transmitter Projecat
USB FM transmitter
To keep the circuit simple as well as compact, it was decided to use a chip made by Maxim Integrated Products, the MAX2606 [1]. This IC from the MAX2605-MAX2609 series has been specifically designed for low-noise RF applications with a fixed frequency. The VCO (Voltage Controlled Oscillator) in this IC uses a Colpitts oscillator circuit. The variable-capacitance (varicap) diode and feedback capacitors
for the tuning have also been integrated on this chip, so that you only need an external inductor to fix the central oscillator frequency.

t is possible to fine-tune the frequency by varying the voltage to the varicap. Not much is demanded of the inductor, a type with a relatively low Q factor (35 to 40) is sufficient according to Maxim. The supply voltage to the IC should be between 2.7 and 5.5 V, the current consumption is between 2 and 4 mA. With values like these it seemed a good idea to supply the circuit with power from a USB port.
Circuit diagram:
MP3-FM-Transmitter-Schematic -Circuit Diagram
USB FM transmitter schematics Circuit diagram
 Parts List
Resistors (all SMD 0805)
R1,R2 = 22kΩ
R3 = 4kΩ7
R4,R5 = 1kΩ
R6 = 270Ω
P1 = 10kΩ preset, SMD (TS53YJ103MR10 Vishay Sfernice, Farnell # 1557933)
P2 = 100kΩ preset, SMD(TS53YJ104MR10 Vishay Sfernice, Farnell # 1557934)
Capacitors (all SMD 0805)
C1,C2,C5 = 4μF7 10V
C3,C8 = 100nF
C4,C7 = 2nF2
C6 = 470nF
L1 = 390nF, SMD 1206 (LQH31HNR39K03L Murata, Farnell # 1515418)
L2 = 2200Ω @ 100MHz, SMD, common-mode choke, 1206 type(DLW31SN222SQ2L Murata, Farnell #1515599)
IC1 = MAX2606EUT+, SMD SOT23-6 (Maxim Integrated Products)
K1 = 3.5mm stereo audio jack SMD (SJ1-3513-SMT
CUI Inc, DIGI-Key # CP1-3513SJCT-ND)
K2 = 5-pin header (only required in combination with 090305-I pre-emphasis circuit)
K3 = USB connector type A, SMD (2410 07 Lumberg, Farnell # 1308875)

A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply. There is not much else to the circuit. The stereo signal connected to K1 is combined via R1 and R2 and is then passed via volume control P1 to the Tune input of IC1, where it causes the carrier wave to be frequency modulated. Filter R6/C7 is used to restrict the bandwidth of the audio signal. The setting of the frequency (across the whole VHF FM broadcast band) is done with P2, which is connected to the 5 V supply voltage.

The PCB designed uses resistors and capacitors with 0805 SMD packaging. The size of the board is only 41.2 x 17.9 mm, which is practically dongle-sized. For the aerial an almost straight copper track has been placed at the edge of the board. In practice we achieved a range of about 6 metres (18 feet) with this. There is also room for a 5-way SIL header on the board. Here we find the inputs to the 3.5 mm jack plug, the input to P1 and the supply voltage. The latter permits the circuit to be powered independently from the mains supply, via for example three AA batteries or a Lithium button cell. Inductor L1 in the prototype is a type made by Murata that has a fairly high Q factor: minimum 60 at 100 MHz.

PCB Layout :
 USB FM transmitter Layout PCB
Take care when you solder filter choke L2, since the connections on both sides are very close together. The supply voltage is connected to this, so make sure that you don’t short out the USB supply! Use a resistance meter to check that there is no short between the two supply connectors before connecting the circuit to a USB port on a computer or to the batteries.

P1 has the opposite effect to what you would expect (clockwise reduces the volume), because this made the board layout much easier. The deviation and audio bandwidth varies with the setting of P1. The maximum sensitivity of the audio input is fairly large. With P1 set to its maximum level, a stereo input of 10 mVrms is sufficient for the sound on the radio to remain clear. This also depends on the setting of the VCO. With a higher tuning voltage the input signal may be almost twice as large (see VCO tuning curve in the data sheet). Above that level some audible distortion becomes apparent. If the attenuation can’t be easily set by P1, you can increase the values of R1 and R2 without any problems. 

Measurements with an RF analyzer showed that the third harmonic had a strong presence in the transmitted spectrum (about 10 dB below the fundamental frequency). This should really have been much lower. With a low-impedance source connected to both inputs the bandwidth varies from 13.1 kHz (P1 at maximum) to 57 kHz (with the wiper of P1 set to 1/10). In this circuit the pre-emphasis of the input is missing. Radios in Europe have a built-in de-emphasis network of 50 μs (75 μs in the US). The sound from the radio will therefore sound noticeably muffled. To correct this, and also to stop a stereo receiver from mistakenly reacting to a 19 kHz component in the audio signal, an enhancement circuit Is published elsewhere in this issue (Pre-emphasis for FM Transmitter, also with a PCB). Author: Mathieu Coustans, Elektor Magazine, 2009
Notice. The use of a VHF FM transmitter, even a low power device like the one described here, is subject to radio regulations and may not be legal in all countries.
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Wire Loop Game

In the ‘Wire Loop Game’, a test of dexterity,  the player has to pass a metal hoop along a  twisted piece of wire without letting the hoop  touch the wire. Usually all the associated electronics does is ring a bell to indicate when the  player has lost. The version described here has  a few extra features to make things a bit more  exciting, adding a time limit to the game and a ticking sound during play. 

Two 555 timer ICs are used to provide these  functions. IC1 is configured as a monostable which controls the time allowed for the  game, adjustable using potentiometer P1. IC2  is a multivibrator to provide the ticking and Two 555 timer ICs are used to provide these  functions. IC1 is configured as a monostable which controls the time allowed for the  game, adjustable using potentiometer P1. IC2  is a multivibrator to provide the ticking and he continuous buzz that indicates when the  player has touched the wire with the hoop. 

Circuit diagram :
Wire Loop Game-Circuit Diagram
Wire Loop Game Circuit Diagram

When the monostable is in its steady state,  the output of IC1 (pin 3) is low. T1 acts as  an inverter, and D2 is thus forward biased.  R8 and R4 are therefore effectively in parallel, with the result that IC2 produces a low audible tone. The value of R4 is considerably  greater than that of R8, and so the frequency  of the buzz generated by IC2 is chiefly deter-mined by the value of R8.

When the monostable is triggered, the high  level at the output of IC1 is again inverted  by T1. D2 is reverse biased and so R8 is effectively removed from the circuit. The frequency of IC2 is now largely determined by  the value of R4. The ratio of R4 to R5 and the  value of C4 affect the mark and space periods for the multivibrator: for a satisfactory  ticking sound short pulses with long gaps  between work well. 

Whether a sound is produced also depends  on the voltage on pin 4 of IC2. When the 9 V  supply is connected the monostable is initially inactive and there is no voltage across  C1. Pin 4 (reset) on IC2 is thus low and no tone  is produced. IC1 is activated by a brief press of  S1, which generates a low-going trigger signal  on pin 2 to start the game. C1 now charges via  D1 and IC2 is allowed to oscillate, generating  the ticking sound. 

The pulse width of the monostable sets the  game duration, and can be adjusted using  P1. If the allowed time expires, or if the reset  input to IC1 is taken low (which happens when the hoop touches the wire), the monostable  returns to the quiescent state. This causes IC2  to generate the low buzz sound. D1 is now  reverse biased and C1 discharges through the  relatively high-valued resistor R9. After a few  seconds the voltage across C1 falls sufficiently  that the buzz stops and the circuit is ready for  the next player. 

The circuit can be built first on a breadboard,  so that the component values can easily be changed to suit particular preferences for  game duration and buzz pitch. When suitable  values have been selected the circuit can be  built more permanently on a printed circuit  board. The author used a sheet of plywood  to form a base for the game, the twisted wire  being fixed to the board and wired to the electronics mounted below it. 

Author: Andreas Binner
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SW Converter for AM Radio

Apart from chucking it in the bin, what can you do with old AM car radio or clock radio in your junkbox? How about turning it into a crystal controlled, stable, short wave radio receiver, for a minimum investment in time and money? Read on. The heart of the circuit shown here is an IC which goes by the name NE602, NE612 or SA612. It is a double balanced mixer that includes an oscillator that can be crystal-controlled, free running or even driven externally from a PLL, etc. It was originally designed for mobile telephones and is probably available in junked car phones from the tip. The NE602/612 contains a differential input amplifier (called a Gilbert Cell), an oscillator/buffer, a temperature compensated bias network and a power regulator. Typical frequency response is in excess of 500 MHz for the input and 100 MHz for the oscillator.
Circuit diagram :
SW Converter for AM Radio-Circuit-Diagram
SW Converter for AM Radio Circuit Diagram
Supply current is 2.4 mA and the absolute maximum supply voltage is 9 V. Input and output impedances are approx. 1.5 kΩ. As you can see from the circuit diagram, the input from the aerial is passed through a 10.7 MHz IF (intermediate frequency) transformer. This gives isolation from the aerial and reduces the effect of strong local AM radio breakthrough.The transformer can be salvaged from a dead FM radio or stereo or even the FM section of an old clock radio. (The AM section is what we want to use anyway so ratting a bit from the FM section saves cost). A number of 10.7 MHz IF coils from Toko and other far-Eastern manufacturers may be used, including the 94AES30465N and 94ANS30466N, but obtaining these as new parts may be more costly than a complete radio rescued from the tip. There is usually a small capacitor under the IFT coil, between the pins. If so, remove it by crushing it with a pair of pliers and ripping out the remains. The capacitor is not needed as we add an external one according to the band wanted. The input signal is fed into the balanced input of the IC.
The crystal is connected to pin 6. It oscillates at its fundamental frequency and is mixed with the input signal giving a number of outputs. The mixer output signal appears on pins 4 and 5. Here, only pin 5 is used for the output. By the way, the inputs and outputs are internally biased with pull-up resistors, so there is no need to tie the unused pins to ground or power. The 220 pF capacitor gives isolation to any DC into the AM radio aerial input. Note also that the same circuit can be used to extend the range of an existing short wave radio receiver in exactly the same manner. The AM radio is used as a tuneable intermediate frequency amplifier, with a tuning range of about 1.6 MHz. You can try different values for C1 to get resonance at the NE602 input: 150 pF for up to 5 MHz, 47 pF for up to 8 MHz, and no capacitor for up to 10 MHz. In practice however 33 pF should do for all ranges. Almost any crystal can be used. The author tried many types from FT-243 WW2 surplus ones to 27 MHz, 3rd overtone CB crystals. Every crystal tried worked. TV sub-carrier crystals work well, as do large oven types. Several crystals can be connected through a switch, giving a convenient way of switching bands. Keep the leads to the switch as short as possible though to prevent radiation of the crystal oscillator. There are many ways to build the circuit. You could make it into an external metal box that can be connected to several radio’s, depending on your location. For instance, if you are a traveller, make it in a small box with an internal 9-volt battery, and leave enough wire on the output to wrap a few dozen turns around the clock radio in your Hotel room.

This will give you your short-wave reception on the go. It is also possible to build the converter right into the car radio. Any sort of construction method can be used, from a small piece of perforated board that I used, to a more elaborate printed circuit board and even just lash all the small components underneath the IC socket. A small switch may be used to change from AM to short-wave. Connect the circuit to the car radio with screened cable to prevent or lessen the effect of strong station breakthrough. To couple the output of the converter to a radio without an external AM aerial input, wind several turns of wire around the internal ferrite rod aerial. As suggested before, winding a dozen or so turns around the plastic radio case will also couple the converter to the radio. This will work at the expense of increased AM signal breakthrough. Connect the positive power lead to the switch on the radio so that it switches the converter on and off as well.

The short-wave aerial can be 2 to 3 meters of wire strung around the room, but better results will be obtained with a outdoor aerial. The test aerial was about 100 meters long and 10 meters high. At night there is a lot of activity on the short waves after dark. Find a weak station around 1 MHz on the AM dial and adjust the core of the IFT for minimum volume from the broadcast station. That’s the only adjustment. SSB signals can be heard, but as no beat frequency oscillator is fitted, you hear the “duck talk” of the signal. The 10 kHz bandwidth of the radio means that on the ham bands, signals do overlap, but it also makes the broadcast stations sound better as most of them do broadcast with reasonable quality audio. Digital tuned AM radios are usually not suitable for the circuit as presented, because the tuning steps are 9 or 10 kHz apart and we want much smaller steps. The old manually tuned types of car radio are what you want. The idea of the circuit is not to get too complicated, but to just enjoy listening on a simple, stable, cheap, short wave receiver. Experiment and enjoy!

Author : P. Laughton, VK2XAN – Copyright: Elektor Electronics
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Power Supply with High Voltage Isolation

Occasionally you come across some unusual  situations when setting up measurement  systems. The author once had to set up a system to register the vibrations and strain supposed to be  present in a contactor that operated at a voltage of 25 kVAC.
One of the biggest problems with this project turned out to be the power supply for  the measurement system. Since it required  a power of about 30 W it wasn’t possible to  use batteries since the system had to operate  for many hours at a time. A logical solution  would seem to be to use an isolating trans-former, but still.25 kVAC means a peak volt-age approaching 40 kV, and on top of that  you would have to include a safety margin. In  addition, everything that is connected to high  voltage lines should also be able to withstand  lighting strikes!
Circuit diagram :
Power Supply with High Voltage Isolation-Circuit Diagram
Power Supply with High Voltage Isolation Circuit Diagram
Consequently the isolation should be able to  cope with a test voltage of 150 kV, which is a  lot to ask of the isolating material.
After extensive research no supplier could be  found for a transformer rated at 50 W, 230 V  primary, 12 V secondary and an isolation of  25 kVAC. Because of this, a dynamic system  had to be used that unfortunately suffers a  bit from wear and tear. This system consists  of a 50 W 3-phase motor connected up via an  isolating drive-shaft to a 30 W generator (a  3-phase servo motor that was used as a generator), which provides the power for the data  logger and associated electronics.
Because a 3-phase generator was used, the  voltage obtained after full-wave rectification (via D1 and D4 to D8) already looked good,  also because the revs of the generator was  fairly high. The secondary supply can there-fore remain fairly simple. The main supply of 9 VDC is stabilised by IC3, an LM317T. From  there it is fed to a few small DC/DC modules  (IC1, IC4, IC5), which supply voltages of +5 V,  +30 V and -9 V, which are required by the other parts of the circuit. IC2 (LM566, a volt-age controlled oscillator) makes LED D2 flash  when the supply voltage is present.pply-with-high-voltage.html
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Wednesday, February 26, 2014

Basic AC Circuits 2nd Edition

As stated in the preface this book is designed primarily for the person continuing a study of basic electricity — the entry level student. It assumes that the reader has a basic knowledge of the principles of direct current (dc) electricity and a basic mathematics background that includes some algebra. There are several features of this book specifically designed to increase its efficiency and help the reader grasp the principles of analyzing ac circuits. At the beginning of each chapter, detailed objectives are listed. These objectives state what new things you should be able to do upon successful completion of the chapter. It is suggested that these objectives be read before beginning the chapter.

Basic AC Circuits 2nd Edition eBookFile Size: 8MB
File Type: PDF
Total Pages: 552
  1. Introduction to Alternating Current
  2. AC and the Sine Wave
  3. The Oscilloscope and Its Use
  4. The Sine Wave and Phase
  5. Resistive Circuits
  6. Capacitance
  7. RC Circuit Analysis
  8. Inductance and Transformers
  9. RL Circuit Analysis
  10. RC and RL Time Constants
  11. RLC Circuit Analysis
  12. Phasor Algebra
  13. Complex RLC Circuit Analysis
  14. Resonance
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Minimalist Dip Meter

In days gone by a radio amateur always had a dip meter close to hand in his ‘shack’. Now that people can afford oscilloscopes, the poor old dip meter has lost its importance and is  frequently no longer to be seen. Actually this is a shame because many tasks are much easier to carry out with a dip meter. Anyone who’s interested (perhaps the second time around) can easily build one rapidly with this very simple but adequate circuit. The interesting question is namely what do you actually need from a dip meter? 

Minimalist Dip Meter-Circuit Diagram Minimalist Dip Meter Circuit Diagram
  • A visual display of the dip? Nope, the ‘scope can handle that task.
  • A large frequency scale? Not necessary, as you can connect a frequency counter for this.
  • A selection of coils? We don’t need these because we can use a jumper to change range (no coils to lose any more!).
The sensor coil L1 has ten turns and is wound  using an AA-size battery as a former. This coil will allow us to over the range from 6 MHz to 30 MHz. With jumper JP1 open an additional fixed inductance of 10 μH comes into circuit. The frequency measurement range is then from 2.5 MHz to 10 MHz. The switch may be replaced by a jumper. 

To take measurements you hold a resonant circuit close to the sensor coil. Tune the rotary capacitor C1 slowly to and fro in order to find the resonant frequency, at which the oscillator amplitude decreases somewhat. The frequency can then be read directly off the oscilloscope.
To obtain a very accurate measurement you can additionally connect your frequency counter to the second output.
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The Gentle Touch Circuit Diagram

Consumer appliances these days hardly ever have a proper mains switch. Instead, appliances are turned on and off at the touch of a button on the remote control, just like any other function. This circuit shows how a device (as long as it does not draw too high a current) can be switched on and off using a pushbutton. The approach requires that a microcontroller is already available in the circuit, and a spare input port pin and a spare output port pin are required, along with a little software. When power is applied T1 initially remains turned off. When the button is pressed the gate of T1 is taken to ground and the p-channel power MOSFET conducts. The microcontroller circuit is now supplied with power. Within a short period the microcontroller must take output PB1 high. This turns on n-channel MOSFET T1 which in turn keeps T1 turned on after the push-button is released.

Now the microcontroller must poll the state of the push-button on its input port (PB0) at regular intervals. Immediately after switch-on it will detect that the button is pressed (a low level on the input port pin), and it must wait for the button to be released. When the button is next pressed the device must switch itself of f: to do this the firmware running in the microcontroller must set the output port pin to a low level. When the button is subsequently released T1 will now turn off and the supply voltage will be removed from the circuit.

The circuit itself draws no current in the off state, and for (rechargeable) battery-powered appliances it is therefore best to put the switch before the voltage regulator. For mains-powered devices the switch can also be fitted before the voltage regulator (after the rectifier and smoothing capacitor). Since there is no mains switch there will still be a small standby current draw in this case due to the transformer. Be careful not to exceed the maximum gate-source voltage specification for T1: the IRFD9024 device suggested can withstand up to 20 V. At lower voltages R2 can be replaced by a wire link; otherwise suitable values for the voltage divider formed by R1 and R2 must be selected.
Circuit diagram:
the-gentle-touch-circuit-diagramw The Gentle Touch Circuit Diagram

The author has set up a small website for this project at, which gives source code examples (which include dealing with pushbutton contact bounce) for AVR microcontrollers suitable for use with AVR Studio and GNU C. Downloads are also available at

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Tuesday, February 25, 2014

Blinking LEDs diagram project

Listening to music on my pc (proudly using WINAMP), I was wondering how would be to have some leds blinking with the sound that came out from the P2 connector, so I decided to make a simple circuit to do that. It worked pretty fine, so I decided to write a HowTo telling step-by-step how to do it. Hope you enjoy it!

Material and Equipment:
  • 4 LEDs (any collor)
  • P2 plug
  • 2 position switch
  • TIP31 component
  • Box to put all the stuff (if you want)
  • Soldering iron and accessories
  • Cable

This project will work this way, you connect 4 leds in the +12V from your computer, they are soldered to a 2 position switch that will connect to a component called TIP31, this component gets the intensity transmitted by the P2 connector, and with that, makes the leds blink with the music.
You can follow this scheme (there are 3 different ones, hope you understand it).


For this project, I decided to install everything inside a small black box I had here, so I made 6 holes on it. Four in the top for leds and one in each side for the switcher and cables. You can follow by the pictures:

With the box ready, its time to connect everything. I started with the leds, soldering one small cable connecting each one, so would be easier to arrange them inside the box after.

After connecting all leds, you must connect the cable coming from the leds to the center pin of the switcher. One side of the switcher goes to the middle pin of the Tip31 component, and the other one goes to ground cable.

Now it’s time to make the P2 connector. You can see that the P2 connector have 3 pins, they are, left channel, right channel and ground. So you have to decide to get the left or right channel and connect with the left pin from the Tip31. Remember that if you connect the P2 using the left channel, if only the right is enabled on the computer, this circuit won’t work. Usually the ground pin is the bigger one, and the other are small and similar. You have to connect the ground from P2 connector to the right pin of the Tip31 (right pin from Tip31 is ground)

On the other pin from the switcher, you must connect to the ground from Tip31. If the switcher if closing circuit with the Tip31, the leds will only blink if there is any signal coming from the P2 connector, and if it’s in the other direction, the leds will be always ON.
Now it’s time to put everything together in the box, as you can see in this picture, it’s not very organized, but after closing the box, it’ll look much better.

Job is done!!

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Sunday, February 9, 2014

Stereo High Power Audio Amplifier

Stereo High Power Audio Amplifier

This is a stereo amplifier circuit which has a high output power and excellent sound quality. Amplifier circuit has a very high gain output stage resulting in the deterioration of signal noise distance. This amplifier circuit having an output power of more than 400 Watt x 2 (Stereo) with the speaker impedance 4 Ohm - 8 Ohm. Power supply voltage circuit to supply this high power amplifier with maximum - + 75 Volt DC. Heres the scheme of High Power Amplifier :

High Power Amplifier Circuit Diagram
High Power Amplifier Circuit Diagram

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SW Converter for Digital AM Car Radio

This circuit is purposely presented with many loose ends (not literally, of course) to stimulate experimenting with RF circuitry at a small outlay. Looking at the circuit diagram you may recognize a modified version of the SW Converter for AM Radios described elsewhere in this issue. The modifications were necessary to make the circuit compatible with a digital rather than analogue AM car radio. The main difference between digital AM radios and their all-analogue predecessors is that tuning is in 9 kHz (some-times 4.5 kHz steps) in compliance with the international frequency allocation for the band. Obviously, that particular step size, desirable as it may be on MW, is a stumbling block if you want to use a digital AM receiver in combination with a frequency step-up converter for SW, where chaos reigns and there is no fixed step size. The first attempt was to make the crystal oscillator variable by about 5 kHz each way.
Circuit diagram :
SW Converter for Digital AM Car-Radio-Circuit-Diagram
SW Converter for Digital AM Car Radio Circuit Diagram
Unfortunately, despite serious efforts, the crystal could not be pulled more than 1 or 2 kHz so another solution had to be found. After studying the NE/SA602/612 datasheet, it was found that a variable LC based oscillator was the best alternative. The circuit worked after winding a resonant LC circuit and adding a 0.1 µF series capacitor to block the DC component on pin 6 of the NE602 (612). When the tuning was found to be a bit sharp with the original capacitor, a simple bandspread (or fine tuning) feature was added by shunting the LC resonant circuit with a lightly loaded 365 pF tuning capacitor (C10) which, like the main tuning counterpart, C8, was ratted from an old transistor radio. The tuning coil, L1, consists of 8 to 10 turns of 0.6-0.8mm dia. enamelled copper wire (ECW) on a 6-8 mm dia. former without a core. With this coil, frequency coverage will be from about 4 MHz to 12 MHz or so. Details on Tr1 may be found in the referring article.
Note that no tuning capacitor is used on the secondary — the input stray capacitance of the NE602 (612) does the trick. A BFO (beat frequency oscillator) was added to enable SSB (single sideband) signals to be received. The BFO built around T1 is simple, has a heap of output and is stable enough to hold an SSB signal for a few minutes without adjustment. The BFO frequency is tuned with C3. Tr2 is a ready-made 455 kHz IF transformer whose internal capacitor was first crushed and then removed with pliers. When S2 is closed the BFO output signal is simply superimposed on the NE602 (612) IF output to the MW radio. The converter should be built into a metal box for shielding. If you find that the BFO gives too much output, disconnect it as suggested in the circuit diagram and let stray coupling do the work. Sensitivity, even on a 1-metre length of car radio aerial, is quite amazing. Bearing in mind that most of the major international SW broadcasting stations like Radio NHK Japan, Moscow, BBC etc.) generate enough power to make sure that you will hear them, it is still quite exciting to hear such signals for the first time on your car radio.
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Battery Voltage Indicator Using SN16889

This battery voltage indicator electronic project is designed using linear voltage indicator SN16889 (manufactured by Texas Instruments) or MC16889 (manufactured by Motorola). The circuit below allows lighting, depending on input voltage of one or more LEDs. Maximum voltage at which all LEDs light is adjusted using potentiometer P1 to 15 volts. D7 can be red LED indicates a battery voltage too high. D6 LED green indicates a correct value and the battery voltage LEDs D5, D4 and D3 yellow indicates a battery voltage too low.

Battery Voltage Indicator Circuit Diagram

SN16889 Battery Voltage Indicator
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Saturday, February 8, 2014

Telephone Ringer

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Car audio amplifier using TDA2003 IC

Car audio amplifier using TDA2003 IC

Easy low power car audio amplifier circuit on TDA 2003. The circuit is Easy to construct. TDA2003 is an integrated radio amplifier from ST Micro electronics that like short circuit protection for all pins, thermal over low harmonic distortion, low cross over distortion etc. In the circuit given here TDA2003 is wired as a mono amplifier operating from a 12V .

Resistors R2 and R3 forms a feedback network that sets the amplifiers gain. C7 input DC de-coupling capacitor and C5 couples the speaker to the amplifiers output. C4 } for improving the ripple rejection C1 and C2 are employed for power filtering. C3 and R1 are used for setting the frequency cut-off. Network comprising of C6 and R4 for frequency stabilization and oscillation.


  • Assemble the circuit on a good quality PCB.
  • Heat sinks are necessary for both ICs.
  • The circuit can be operated from 12V DC.
  • S1 is the ON/OFF switch.
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Audio Controlled Mains Switch

It is often useful for audio or video equipment to be switched off automatically after there has been no input signal for a while. The function of the on-off switch in such equipment is then taken over by switch S2 in the accompanying diagram. It remains, however, possible to  switch off manually by means of Si. Automatic  switch-off occurs after there has been no input  signal for about 2 minutes: this delay makes it possible for a new record or cassette to be placed in the  relevant machine.
The audio input to the proposed circuit may be  taken from the output of the relevant TV set, amplifier, or whatever. The input earth is held at + 6 V  with respect to the circuit earth by potential divider  Ri-R2-R3-R4. The two 741s function as comparators: the output of ICi goes high when the in- put signal is greater than + 50 mV, whereas the out- put of IC2 goes high when the input signal  becomes more negative than -50 mV. Resistors  R6, R7, and R8 form an OR gate that drives transistor Ti. If the output of either ICi or IC2 is logic  1, Ti conducts.
Circuit diagram :
Audio Controlled Mains Switch Circuit Diagram

The 555  operates as a retrigger able monostable,  whose period is determined by Rio and Ci. The  device is triggered when its pin 2 is earthed by the  closing of S2. Its output, pin 3, then remains high  for 1 to 2 minutes, depending on the leakage cur- rent of the 555. 

The monostable resets itself as soon  as the potential across Ci exceeds a certain value.  As long as there is an input signal to the circuit, Ti conducts and Ci remains uncharged. As soon as  the audio signal ceases, Ti switches off, and Ci  charges until the potential across it is sufficient to  reset the 555. The monostable may also be reset by  closing Si, which connects pin 6 of the 555 to + 12 V.
When IC3 is reset, Ci is discharged via its pin 7. Resistor Rrn serves as protection, because without it Ti could short-circuit the supply lines. When the output of IC3 goes high, T2 conducts,  the relay is energized, and the relay contacts switch on the mains voltage as appropriate. To counter the induced potential when the relay contacts close, which could damage T2, diode Di has been connected in parallel with the relay coil.
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Friday, February 7, 2014

Three Phase Generator regulator

This regulator was designed for use with a  generator with a higher output voltage. This  type of generator can be found on some boats  and on vehicles for the emergency services.  They are really just an adapted version of the  standard alternator normally found in cars.  The field winding is connected to the 12 V  (or 24 V) battery supply, whereas the generator winding is configured for the AC grid  voltage (230 V or 115 V). This AC voltage now  has to be kept stable via the 12 V field winding. Although it’s perfectly possible to use a  switching regulator for this, we deliberately  chose to use the old and trusted 723.
Circuit diagram :
Regulator for Three-Phase Generator-Circuit Diagram
Regulator for Three-Phase Generator Circuit Diagram
The generator is a three-phase type, with the  field winding rated for 12 VDC. The output voltage of the generator depends on its revs  and the current through the field winding.  Since the output voltage is relatively high, it  is fed via opto-couplers to the 723, which is  used in a standard configuration.  The output is fed via driver T1 to two  2N3055’s, connected in parallel, which sup-ply the current to the field winding. In the prototype we used TLP620 opto-couplers. These are suitable for use with alternating voltages because they have two anti-parallel LEDs at the input. The regulation works  quite well with these, with the output volt-age staying within a small range across a wide  range of revs.
However, the sensitivity of the two internal  LEDs can differ in this type of opto-coupler,  since it’s not always possible to ensure during  the manufacturing process that the distance  between each LED and the phototransistor is  exactly the same. For a more precise regulation it would be better to use two individual  opto-couplers per phase, with the inputs connected in anti-parallel and the outputs connected in parallel.
In order to ensure that there is sufficient isolation between the primary and secondary side  you should make a cutout in the PCB underneath the middle of each opto-coupler. Instead of a BD136 for T1 you could also use  a TIP32 or something similar. For T2 and T3  it’s better to use a type with a plastic casing,  rather than a TO3 case.
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Stereo TDA2822 audio power amplifier circuit

Stereo TDA2822 audio amplifier circuit
In this series I use IC tda2822M as the main amplifier, but if you want to use in addition to IC TDA2822M you can use ic I mentioned this is KA2209, NJM2073, U2822B, U2823B. Output is issued no more than 4W, which had low output. Supply voltage from 3 volts to 16 volts.

Below its schematics of TDA2822 stereo audio power amplifier

TDA2822 amplifier schematics

Part description
R1 = 4.7R
R2 = 4.7R
C1 = 1uF
C2 = 100uF
C3 = 100uF
C4 = 0.1uF
C5 = 470uF
C6 = 1uF
C7 = 100uF
C8 = 0.1uF
C9 = 470uF
ICs = KA2209 , NJM2073 , TDA2822 , U2822B , U2823B
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Digital Fan Regulator

The circuit presented here can be used to control the speed of  fans using induction motor. The speed control is nonlinear, i.e. in steps. The current step number is displayed on a 7-segment display. Speed can be varied over a wide range because the circuit can alter the voltage applied to the fan motor from 130V to 230V RMS in a maximum of seven steps.  The triac used in the final stage is fired at different angles to get different voltage outputs by applying short-dura-tion current pulses at its gate. For this pur-pose a UJT relax-ation oscillator is used that outputs sawtooth waveform. This waveform is coupled to the gate of the triac through an optocoupler (MOC3011) that has a triac driver output stage. 

Pedestal voltage control is used for varying the firing angle of the triac. The power supply for the relaxation oscillator is derived from the rectified mains via 10-kilo-ohm, 10W series dropping/limit-ing resistor R2.  The pedestal voltage is derived from the non-filtered DC through optocoupler 4N33. The conductivity of the Darlington pair transistors inside this optocoupler is varied for getting the pedestal voltage. For this, the positive sup-ply to the LED inside the optocoupler is connected via different values of resistors using a multiplexer (CD4051). 

Digital Fan Regulator Circuit Diagram
Digital Fan Regulator Circuit Diagram

The value of resistance selected by the multiplexer depends upon the control in-put from BCD up-/down-counter CD4510 (IC5), which, in turn, controls forward bi-asing of the transistor inside optocoupler 4N33. The same BCD outputs from IC5 are also connected to the BCD-to-7-seg-ment decoder to display the step number on a 7-segment display.  NAND gates N3 and N4 are config-ured as an astable multivibrator to produce rectangular clock pulses for IC5, while NAND gates N1 and N2 generate the active-low count enable (CE) input using either of push-to-on switches S1 or S2 for count up or count down operation, respectively, of the BCD counter. 

Optocoupler 4N33 electrically isolates the high-voltage section and the digital section and thus prevents the user from shock hazard when using switches S1 and S2. BCD-to-7-segment decoder CD4543 is used for driving both common-cathode and common-anode 7-segment displays. If phase input pin 6 is ‘high’ the decoder works as a common-anode decoder, and if phase input pin 6 is ‘low’ it acts as a common-cathode decoder.  Optocoupler 4N33 may still conduct slightly even when the display is zero, i.e. pin 13 (X0, at ground level) is switched  output pin 3. To avoid this problem, adjust preset VR1 as required using a plastic-handled screwdriver to get no output at zero reading in the display.
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How to Diagnose and Fix Everything Electronic

Everything. That’s a scary word, one I almost avoided including in the title. Can any book actually cover everything about a topic? Yes and no. Yes, in the sense that the principles and techniques you’ll learn can be applied to the repair of every kind of consumer electronics device presently being made or likely to be sold in the near future. No, in that it’s impossible to fit each of the thousands of types of components and countless varieties of gadgets in the world into one volume. Covering all of them in deepest detail would take a library, and a good-sized one at that.

How to Diagnose and Fix - Everything Electronic eBookFile Type: PDF
File Size: 3.4MB
Total Pages: 337

Chapter 1
  • Prepare for Blastoff: Fixing Is Fun!
Chapter 2
  • Setting Up Shop: tools of the trade
Chapter 3
  • Danger, Danger! Staying Safe
Chapter 4
  • I Fix, therefore I am: the philosophy of troubleshooting
Chapter 5
  • Naming Names: Important terms, Concepts and Building Blocks
Chapter 6
  • Working Your Weapons: Using test equipment
Chapter 7
  • What Little Gizmos are Made of: Components
Chapter 8
  • Roadmaps and Street Signs: Diagrams
Chapter 9
  • Entering Without Breaking: Getting Inside
Chapter 10
  • What the heck Is that? recognizing Major Features
Chapter 11
  • A-hunting We Will Go: Signal tracing and Diagnosis
Chapter 12
  • Presto Change-O: Circuit Boards and replacing Components
Chapter 13
  • That’s a Wrap: reverse-Order reassembly
Chapter 14
  • Aces Up Your Sleeve: tips and tricks for Specific products
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Thursday, February 6, 2014

Power Supply Variable 1 3V 12 2V 1A Circuit

Power supply circuit to generate output below were variations between 1.3V DC to 12.2V DC with 1A current. In addition, the power supply circuit is also equipped with over-current protection or shield against belebih flow. Power supply circuit is very simple, but the quality is quite good, made her basiskan regulator IC LM723 is a pretty legendary.

1.3V DC to 12.2V DC Regulator Power Supply


R2 to set the output voltage. The maximum current is determined by R3, over-current protection circuit inside the LM723 to detect the voltage on R3, if it reaches 0.65 V, the voltage output will be off her. So the current through R3 can not exceed 0.65 / R3 although output short-circuit in his.

C3 and C4 are ceramic capacitors, as much as possible directly soldered to the PCB, this is because the LM723 is prone to oscillation that is not cool.

LM723 works with 9.5V input voltage to 40 V DC and the LM723 can generate its own current of 150mA when the output voltage is not more than 6-7V under input voltage.


Output (value estimated):

Vmin = (R4 + R5) / (R5 * 1.3)

Vmax = (7.15 / R5) * (R4 + R5)

Imax = 0.65/R3

Max. Power on R3: 0.42/R3

Min. DC Input Voltage (pin 12 to pin 7): Vmax + 5

Component List:

B1 40V/2.5A

C1 2200uF (3300uF even better)

C2 4.7uF

C3 100nF

C4 1NF

C5 330nF

C6 100uF

Green LED D1

D2 1N4003

F1 0.2A F

F2 2A M

IC1 LM723 (in a DIL14 plastic package)

R1 1k

R2 Pot. 5k

R3 0.56R/2W

R4 3.3k

R5 4.7k

S1 250V/1A

T1 2N3055 on a heatsink 5K / W

TR1 220V/17V/1.5
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Digital Alarm Clock Using PIC

This project describes a digital clock with alarm function. It uses a PIC16F877 microcontroller to generate an accurate 1 sec delay with Timer0 using Roman’s zero error method. The time is displayed in large size font on a 4×20 character LCD that uses HD44780 display driver. You can synchronize the time with your computer time through a serial port.

Digital Alarm Clock Using PIC Circuit Diagram

The required power is provided through a 9 V wall adapter which is used to obtain a regulated +5 V power supply using a LM7805 IC. The microcontroller runs with a 20 MHz external clock. The backlight of LCD is driven by a PWM output from the microcontroller so that the back light intensity can be varied. The full software written in JAL is available to download. Source Code.
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AM Receiver Schematic

This is a compact three transistor, regenerative receiver with fixed feedback. It is similar in principle to the ZN414 radio IC which is now no longer available. The design is simple and sensitivity and selectivity of the receiver are good.

AM Receiver Schematic

All general purpose transistors should work in this circuit, I used three BC109C transistors in my prototype.The tuned circuit is designed for medium wave. I used a ferrite rod and tuning capacitor from an old radio which tuned from approximately 550 - 1600kHz. Q1 and Q2 form a compund transistor pair featuring high gain and very high input impedance. This is necessary so as not to unduly load the tank circuit.

The 120k resistor provides regenerative feedback,between Q2 output and the tank circuit input and its value affects the overall performance of the whole circuit. Too much feedback and the circuit will become unstable producing a "howling sound". Insufficient feedback and the receiver becomes "deaf". If the circuit oscillates,then R1s value may be decreased; try 68k. If there is a lack of sensitivity, then try increasing R1 to around 150k. R1 could also be replaced by a fixed resisor say 33k and a preset resistor of 100k. This will give adjustment of sensitivity and selectivity of the receiver.

Transistor Q3 has a dual purpose; it performs demodulation of the RF carrier whilst at the same time, amplifying the audio signal. Audio level varies on the strength of the received station but I had typically 10-40 mV. This will directly drive high impedance headphones or can be fed into a suitable amplifier.

All connections should be short, a veroboard or tagstrip layout are suitable. The tuning capacitor has fixed and moving plates. The moving plates should be connected to the "cold" end of the tank circuit, this is the base of Q1, and the fixed plates to the "hot end" of the coil, the juction of R1 and C1. If connections on the capacitor are reversed, then moving your hand near the capacitor will cause unwanted stability and oscillation.

Finally here are some voltagee checks from my breadboard prototype.This should help in determining a working circuit:

All measurements made with a fresh 9volt battery and three BC109C transistors with respect to the battery negative terminal.

Q1 (b) 1.31V
Q2 (b) 0.71V
Q2 (c) 1.34V
Q3 (b) 0.62V
Q3 (c) 3.87V
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Wednesday, February 5, 2014

Schematic Audio Power Amplifier with IC AN7105

This Schematic Circuit Audio Amplifier use IC AN7105 , minimum voltage 1,5 volt and maximum voltage 9,5 volt. This is a low voltage Amplifier , with output speaker stereo 2 X 0,38 watt . Its so low power amplifier. Impedance speaker is 32 Ohm ,with Frequency 20 Hz -20 kHz.

See this Circuit and package IC AN7105 below :

Package IC is DIP-18

Click to view Enlarge

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Blinking LED circuits

Blinking led circuit
This led series will Blinking alternately, The way it works is determined by IC NE555 and transistors are used as reinforcement for each section (20 upper, 20 lower) work optimally. 555 circuit below is a flashing bicycle light powered with four C, D or AA cells (6 volts). 

Two sets of 20 LEDs will flash alternately at about 4.7 cycles per second using RC values ​​shown (4.7K for R1, 150K for R2 and 1uF capacitor). Time intervals for two lights about 107 milliseconds (T1, LED on) and 104 milliseconds (T2 lower LEDs). 

flip flop schematics

Two transistors are used to provide additional time beyond the current limit of 200mA from the NE555 timer. A single LED is placed in series with the PNP transistor base so that the 20 LED 555 is turned off when the output is high during a time interval T1. High-level output timer 555 is 1.7 volts less than the supply voltage. Adding the LED forward voltage increase is required for the PNP transistor to about 2.7 volts, so the 1.7 volt difference from the supply to the output is not sufficient to activate the transistor.
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Basic Principles of the LC resonance circuit

If so far you are still confused how the actual origin of the resonance between the capacitor and the inductor is in progress, then the simple circuit above will answer your confusion.

Basic Principles of the LC resonance circuit

By understanding a simple electrical circuit above hopefully we will be able to understand the working principle of a series of more complicated and complex that uses the relationship as a series inductor and capacitors transmitter and receiver.

Note the picture above, when the switch SW1 is pressed and released back then obtained by the same signal as in the picture above signal. Initially when SW1 is connected to the voltage supply, the capacitor will make filling fast. Then when SW1 is released charge on the capacitor will be used by the inductor as the supply voltage. In accordance with the general nature of the inductor that the DC signal will be considered ordinary wire inductor such that current flowing quickly through the inductor and the charge on the capacitor decreases rapidly exhausted. Uniquely current that was flowing through the inductor and capacitor will fill the empty capacitor back through the other terminal (negative cycle). Charging kapasior place quickly, then inductor will burden the back so that emptying of cargo going back. That so happens repeatedly (resonance occurs between L and C) until the electrical charge had been used up by these two components in the form of power losses. Equations between regular wire inductor is the inductor with wire work as usual at the time of current flowing to him. Inductors But unlike ordinary wire when current flows to him and vice versa. So it will not happen short circuit if the inductor to get the supply voltage alternating current (AC). But in ordinary wire short circuit will still occur even if the voltage of alternating current.

From the above analysis we can conclude that the LC resonance occurs because one component part affected by the characteristics of other components. For frequencies generated depend on the value of L and C itself. The greater the value of both the frequency will be smaller and smaller the value of both the frequency value will be even greater.
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Automatic TV Lighting Switch

The author is the happy owner of a television set with built-in Ambilight lighting in the living room. Unfortunately, the television set in  the bedroom lacks this feature. To make up for this, the author attached a small lamp to the wall to provide background lighting, This makes  watching television a good deal more enjoyable, but it ’s  not the ideal solution. Although the TV set can be  switched off with the remote  control, you still have to get out of bed to switch off the lamp.

Circuit diagram :
Automatic TV Lighting Switch-Circuit-Diagram

Automatic TV Lighting Switch Circuit Diagram

Consequently, the author devised this automatic lighting switch that switches the background light on and off along with the T V set. The entire circuit is fitted in series with the mains cable of the TV set, so there’s no need to tinker with the set. It works as follows: R1 senses  the current drawn by the TV  set. It has a maximum value  of 50 mA in standby mode,  rising  to around   500 m A  when  the  set  is  operating. The voltage across R1 is limited by D5 during negative  half- cycles  and  by  D1– D4  during positive half-cycles.  T he  voltage  across  these  four diodes charges capacitor C1 via D6 during positive  half-cycles. This voltage drives the internal LED of solid-state switch TRI1 via R2, which causes the internal triac to conduct and pass the mains voltage to the lamp.   Diode D7 is not absolutely necessary, but  it is recommended because the LED in the  solid-state switch is not especially robust  and cannot handle reverse polarisation. Fuse  F1 protects the solid-state switch against  overloads. T he  value  of  use d  here  (10 Ω)  for  resistor R1 works nicely with an 82-cm (32 inch)  LCD screen.

With smaller sets having lower  power consumption, the value of R1 can be  increased to 22 or 33 Ω, in which case you  should use a 3-watt type. Avoid using an  excessively high resistance, as otherwise TRI1 will switch on when the TV set is in standby mode.  Some TV sets have a half-wave rectifier in the  power supply, which places an unbalanced  load on the AC power outlet. If the set only  draws current on negative half-cycles, the cir-cuit won’t work properly. In countries with  reversible AC power plugs you can correct  the problem by simply reversing the plug. Compared with normal triacs, optically cou-pled solid-state relays have poor resistance  to high switch-on currents (inrush currents).

For this reason, you should be careful with  older-model TV sets with picture tubes (due  to demagnetisation circuits). If the relay fails,  it usually fails shorted, with the result that the TV background light remains on all the time. If you build this circuit on a piece of perf-board, you must remove all the copper next  to conductors and components carrying  mains voltage. Use PCB terminal blocks with a spacing of 7.5 mm. This way the separation between the connections on the solder  side will also be 3 mm. If you fit the entire  arrangement as a Class II device, all parts of  the circuit at mains potential must have a  separation of at least 6 mm from any metal  enclosure or electrically conductive exterior  parts that can be touched.

Author :Piet Germing - Copyright : Elektor
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Tuesday, February 4, 2014

Simple Circuit Transistor Checker

This simple circuit has helped me out on many occasions. It is able to check transistors, in the circuit, down to 40 ohms across the collector-base or base-emitter junctions. It can also check the output power transistors on amplifier circuits.

Simple Circuit Transistor Checker Schematic

Circuit operation is as follows. The 555 timer ( IC1 ) is set up as a 12hz multi vibrator. The output on pin 3 drives the 4027 flip-flop ( IC2). This flip-flop divides the input frequency by two and delivers complementary voltage outputs to pin 15 and 14. The outputs are connected to LED1 and LED2 through the current limiting resistor R3. The LEDs are arranged so that when the polarity across the circuit is one way only one LED will light and when the polarity reverses the other LED will light, therefore when no transistor is connected to the tester the LEDs will alternately flash.

The IC2 outputs are also connected to resistors R4 and R5 with the junction of these two resistors connected to the base of the transistor being tested. With a good transistor connected to the tester, the transistor will turn on and produce a short across the LED pair. If a good NPN transistor is connected then LED1 will flash by itself and if a good PNP transistor is connected then LED2 will flash by itself. If the transistor is open both LEDs will flash and if the transistor is shorted then neither LED will flash.
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3 Volt Operated Power Amplifier Circuits

This is an audio amplifier with the purpose of can live used with a minor 3 volt Battery Operated,Current get through having the status of not much as 5 milliamps.And amplification up to 500 mW.

3 Volt Operated Power Amplifier Circuit Diagram
3 Volt Operated Power Amplifier Circuit Diagram
Which is sufficient to swell the sound from a sound a propos otherwise the disc totter work comatose to the minor speakers obviously. 3 whilst entering the power supply 3-volt circuit IC1 numeral LM386 amplifier IC size is 300-800 mW, Depending on the power supply circuit with,This is from 3-15 volts. just the once entered into the input pin 3,The non inverting pin to amplifier non-return segment.C1 self-control ensue served slice out the blare input to ground.And C2 increases the rate of amplifier,C2 is to add extra denomination.But if the C2 Too much distortion (the C2 be supposed to not exceed 100uF).The output of IC1 is comatose of the pin 5 through C4 coupling audio signals to better and DC frustrate and not voted for to the narrator.on behalf of the audio portion desire in addition be present fed back through R2 and C3 to the extraordinary frequency response better.
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