This is the circuit connection of home telephone call recorder that uses very few components. In order to understand its working, we must first have the basic knowledge of standard telephone wiring and a stereo plug. In some countries, landline telephones primarily use RJ11 wiring, which has two wires??”tip and ring. While tip is the positive wire, ring is the negative one. And together they complete the telephone circuit. In a telephone line, voltage between tip and ring is around 48V DC when handset is on the cradle (idle line). In order to ring the phone for an incoming call, a 20Hz AC current of around 90V is superimposed over the DC voltage already present in the idle line.

The negative wire from the phone line goes to IN1, while the positive wire goes to IN2. Further, the negative wire from OUT1 and the positive wire from OUT2 are connected to the phone. All the resistors used are 0.25W carbon film resistors and all the capacitors used are rated for 250V or more. The negative terminal of “To AUX IN” is connected to pin 1 of the stereo jack while the positive terminal is connected to pins 2 and 3 of the stereo jack. This stereo jack, in turn, is connected to the AUX IN / Audio Input of any recording device, such as computer, audio cassette player, CD player, DVD player, etc. In this case, we will use a computer desktop / notebook to make a call record.

When a call comes in, around 90V AC current at 20Hz is superimposed over the DC voltage already present in the idle line. This current is converted into DC by the diodes and fed to resistor R1, which reduces its magnitude and feeds it to LED1. The current is further reduced in magnitude by the resistor R2 and fed to the right and left channels of the stereo jack, which are connected to the AUX IN / Audio In port of a computer, in most of notebook devices, it is same between Audio Input / Mic Input.

Any audio recording software can be used to record the home telephone call, i.e AVS Audio Editor, Audacity Audio Recorder, or Audio Recorder for Free. When a call comes in, one needs to launch the audio recording software and start recording.

For phone recording, simply connect the stereo jack to the “audio input” or “mic input” port of the PC/Notebook. Install the audio recorder software on your PC/Notebook. Run the software and check the setting to ensure that the input is correct. Now you are ready to record any call. As soon as a call comes in, press the record button on the software and then pick up the telephone receiver and answer the call. Press the stop button once the call ends and then save the file in a desired location. Each software may has different setting, you can read the manual of each software about how to record an audio.

You may change the value of resistor R2 if you want to change the output volume. You can use a variable resistor in series with R2 to vary the volume of the output the home telephone call recorder circuit. The recorded audio clip can be edited using different options in the Audio Recorder software.

You can built the circuit on a general-purpose PCB and enclose it in a small box. Use an RJ11 connector and stereo jack for connecting the telephone set and computer desktop/laptop (for call recording). Telephone cords can be used to connect to the phone line and the home telephone call recorder circuit. Use of a shielded cable is recommended to reduce disturbances in the recording so it we will get good audio performance from the recording. These disturbances can also be reduced by increasing the value of R2 to about 15K.

This circuit was tested, come from EFY mag, Dec 2009. Download the PDF version:

Home Telephone Call Recorder Circuit Project

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This is the schematic diagram of Infrared (IR) cordless headphone. Maybe it also can be called “wireless headphone”, but it use infrared as sound signal carrier. It use a pair of circuit diagrams that are IR transmitter and IR reveiver. Using this low-cost project one can reproduce audio from TV or other electronic devices without disturbing others. It does not use any wire connection between TV and headphones. In place of a pair of wires, it uses invisible infrared light to transmit audio signals from TV to headphones. Without using any lens, a range of up to 6 metres is possible. Range can be extended by using lenses and reflectors with IR sensors comprising transmitters and receivers.

IR transmitter uses two-stage transistor amplifier to drive two series-connected IR LEDs. An audio output transformer is used (in reverse) to couple audio output from TV to the IR transmitter. Transistors T1 and T2 amplify the audio signals received from TV through the audio transformer. Low impedance output windings (lower gauge or thicker wires) are used for connection to TV side while high-impedance windings are connected to IR transmitter. This IR transmitter can be powered from a 9-volt mains adapter or battery. Red LED1 in transmitter circuit functions as a zener diode (0.65V) as well as supply-on indicator.

IR receiver uses 3-stage transistor amplifier. The first two transistors (T4 and T5) form audio signal amplifier while the third transistor T6 is used to drive a headphone. Adjust potensiometer VR2 for maximum clarity.

Direct photo-transistor towards IR LEDs of transmitter for maximum range. A 9-volt battery can be used with receiver for portable operation.

Good luck…

This kind of circuit is a helpful device for testing of infrared (IR) based remote control transmitters utilized for TVs and VCRs and so forth. The IR motions from a remote control transmitter are sensed by the IR sensor module in the analyzer and its output at pin 2 goes low. This thusly switches on transistor T1 and reasons LED1 to squint. In the meantime, the signal beeps at the same rate as the approaching signs from the remote control transmitter. The pressing of diverse catches on the remote control will bring about distinctive beat rates which might change the rate at which the Led eye flickers or the ringer beeps.

The point when no sign is sensed by the sensor module, output pin 2 of the sensor goes high and, accordingly, transistor T1 switches off and thus LED1 and signal BZ1 go off. This circuit obliges 5v controlled power supply which could be gotten from 9V eliminator and joined with the circuit through a jack.

Capacitor C1 smoothes DC input while capacitor C2 stifles any spikes showing up in the input supply.

Legitimate crushing of the metal case will guarantee that the electromagnetic outflows which are transformed by tube-lights and electronic balances and so forth (which lie inside the data transmission of collector circuit) and rehashes the steps demonstrated in step 1 above and notes down his new score (say, X2). He includes this score to his past score. The same method is rehashed by player “Y” in his turn. 4. The diversion carries on until the score achieved by one of the two players adds up to up to or surpasses 100, to be announced as the victor.

A few players can partake in this amusement, with each one getting an opportunity to score throughout his own particular turn. The circuit may be collected utilizing a multipurpose board. Fix the showcase (LEDs and 7-portion show) on top of the bureau plus the three switches. The supply voltage for the circuit is 5v. are successfully crushed and don’t meddle with the working of the circuit. The proposed layout of the crate holding the circuit is demonstrated in the figure. The 9v DC supply from the eliminator might be bolstered into the jack utilizing a banana kind of plug.

Here is the remote control tester circuit. This circuit is really a simple and easy tester for verifying the basic operations of an infrared remote control unit. It is low-cost and very easy to construct.

The tester is designed around infrared receiver module TSOP1738. Operation of the remote control is identified by a tone from the buzzer. The circuit is sensitive and has a range of about 5 metres. The integrated IR receiver detects, amplifies and demodulates IR signals from the remote control unit. The piezobuzzer connected at its output sounds to tell us the existence of transmission from the remote control unit.

As displayed in above circuit diagram, output pin 3 of IR receiver module TSOP1738 (IRX1) normally stays high and the piezobuzzer is in silent mode. When the IR module IRX1 receives an infrared signal, its output is going low and, because of this, the piezobuzzer sounds to signify the reception of transmission from the remote (for example television remote control unit).

Power supply for the circuit is taken from the mains making use of a capacitive potential dropper, a half-wave rectifier, a shunt regulator and related parts. Ensure that capacitor C1 is of X2 type. Work with a appropriately small enclosure for making the unit handy.

Assemble the circuit on a general purpose PCB and enclose inside a box. Ensure that the IR receiver module is positioned around the front panel of the box/cabinet so that it can get the IR signals easily. Well, before soldering/connecting the shunt regulator and IR module, please check up the following TL431 and TSOP1738 pin configuration.

Here the long range/distance Infrared transmitter circuit, give you extra power for your Infrared transmitter. The majority of the IR remotes do the job reliably within a range of 5 metres. The circuit complexity increases in case you design the IR transmitter for good operation more than a extended distance, for example, 10 metres. To double the distance from 5 metres to 10 metres, it is advisable to enhance the transmitted power 4 times.

In case you want to realise a highly directional IR beam (very narrow beam), you could suitably make use of IR laser pointer as the IR signal source. The laser pointer is readily offered in the marketplace. Even so, using a very narrow beam from the laser pointer, you will need to take special care, lest a small jerk to the gadget may change the beam positioning and lead to loss of contact. Right here is really a simple circuit which will provide you with a fairly long distance. It utilizes three infrared transmitting LEDs (IR1 through IR3) in series to improve the radiated power. Further more, to improve the directivity and so also the power density, you may construct the IR LEDs inside the reflector of a torch.

For improving the circuit performance, a MOSFET (BS170) has been applied, which works as being a switch and thus minimizes the electrical power loss that would happen if a transistor were being applied. To prevent any drop while in its “on”/”off” operations, a 100uF reservoir capacitor C2 is used across the battery source. Its benefit is going to be more obvious if the IR transmitter is operated by common batteries. Capacitor C2 provides additional charge while in “switching on” processes.

Since the MOSFET exhibits big capacitance across gate-source terminals, a particular drive arrangement has been built implementing NPN-PNP Darlington pair of BC547 and BC557 (as emitter followers), to prevent distortion of the gate drive input. Data (CMOS-compatible) for being transmitted is utilized for modulating the 38 kHz frequency produced by CD4047 (IC1). Even so, in the circuit shown here, tactile switch S1 has been utilized for modulating and transmitting the IR signal.

Assemble the circuit on a standard PCB. Use switch S2 for power “on”/”off” control. Commercially available IR receiver modules (e.g., TSOP1738) can be utilized for effective reception of the transmitted IR signals.

Download long range/distance infrared transmitter circuit document PDF:

Long Distance IR Transmitter Circuit Document

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This is a low-cost and simple intercom circuit design. Some intercom circuits is build by applying integrated circuits. The circuit described right here utilizes 3 certainly transistors which easy to find on the electronic store. Even a newbie can assemble it on a piece of veroboard without difficulty.

The circuit consists of a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pushed, the amplifier circuit designed close to transistors T1 and T2 becomes converted into an asymmetrical astable multivib-rator producing ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece.

This intercom circuit only consume electric current about 10 to 15 mA. Therefore a 9-volt PP3 battery would possess a long lifespan, when utilized in this circuit.

For constructing a two-way intercom circuit, two similar units, as shown in figure, are needed for being applied. Output of one amplifier unit connected to speaker of the other unit, and vice versa. For single-battery operation, join corresponding supply and ground terminals of both the units together.

The entire circuit, together with microphone and earpiece etc, could be assembled inside the plastic body of a toy cellphone, that is easily obtainable in the market. Recommended cellphone cabinet, with the placement of switches, speakers, microphone, etc is shown on following image.

Remote Control Transmitter Circuit

The transmitter circuit is constructed around two BC558 transistors (T1 and T2), 3 BC548 transistors (T3, T4 and T5), IR LED1 and a several discrete components.

In the transmitter circuit, you will find two astable multivibrators. The first,designed around transistors T1 and T2, generates a frequency of about 1.2 kHz. The 2nd, designed around transistors T3 and T4, generates about 38 kHz. IR LED1 is utilized to transmit the 38kHz frequency.

Remote Control Receiver Circuit

The Receiber circuit is constructed around IR receiver module TSOP1738, two BC548 transistors (T6 and T7) and a several discrete components.

In the receiver circuit, TSOP1738 receives the IR signal transmitted by IR LED1 of the transmitter circuit. The output of TSOP1738 is fed to transistor T6 through diode D1. The amplified signal is further provided to relay-driver transistor T7. Relay RL1 energises to control the toy car.

Working of the receiver circuit is very simple. At first, when no IR beam is falling on sensor TSOP1738, the relay stays de-energised and the toy car does not move. When switch S1 is pressed, the IR beam falls on TSOP1738 and its output goes low. Transistor T6 cuts off and transistor T7 conducts to energise relay RL1 and move the toy car.

Download the article of toy car remote control circuit design from the following link:
? Toy Car Remote Control

Laser Transmitter Circuit
Here the circuit diagram of laser transmitter

A laser diode (LD1) with maximum operating voltage of about 2.6V DC and maximum operating current of 45 mA is applied to transmit the audio signal. The voltage divider network formed by R2, R3 and VR3 keeps the voltage and also the current for the laser diode in the secured spot.

In place of the laser diode, it is possible to also use a laser pointer. Take out the battery from the laser pointer. Extend two wires from terminals of LD1 and connect them towards the battery terminals of laser pointer. The spring within the laser pointer will be the negative terminal. The output power of the laser pointer is 5 mW. Be careful when doing work with laser, as direct exposure to the laser beam could be hazardous to your eyes. Point the laser beam to the solar panel.

Potmeter VR1 (10-kilo-ohm) is applied to adjust the level of the input audio signal. The audio input (Vin) is taken from the preamplifier output of the music system (CD player, DVD player, etc). Capacitor C2 and preset VR2 are applied to vary the gain of the LM386.

Laser Receiver Circuit
Here the circuit diagram of laser receiver:

The audio signal transmitted by the laser diode (LD1) is received by the calculator”s solar panel and amplified by IC2. The gain of the amplifier is fixed by capacitor C7. Preset VR4 is utilized to adjust the signal level from the solar panel. This signal is fed to input pin 3 of IC2 via coupling capacitor C5 so that the DC value from the solar panel could be eliminated. The amplified output from IC2 is fed towards the speaker, which plays the music from the CD player linked on the input (Vin) of IC1.

This Laser Communication (Transmitter – Receiver) is already tested and claimed to be work.

You can download the circuit in PDF document from the following link:
? Laser Communication System Circuit

This diagram is the schematic diagram of telephone switcher using relays. This device connects to the telephone line and can be used to remotely control up to 4 relay outputs using a DTMF (tone dialing) telephone. A number of user settings are available to improve the useability and security of the device. The kit comes complete with a small plastic case with silk-screened front and rear panels.

The brain of this circuit is microcontroller chip Atmel MCS51 family AT89C2051. The source code is not available here, you may find out the source code by yourself.

The diagram is quite hard to designed in PCB, you may purchase the telephone switcher kits from this page:? http://electronickits.com/kit/complete/tele/ck603.htm

The application notes for this circuit can be download here

Telephone Amplifier Diagram

A volume control for this telephone amplifier is included to adjust the volume as desired. The circuit is built around IC LM386. Diodes D6 and D7 are implemented to limit the input signal strength. Transformer X1 can be a transistor radio”s output transformer used in reverse. As original secondary (output) winding is connected in series with the phone lines, the speech signals passing through the lines cause alteration inside the magnetic flux in the core of transformer and thereby induce signal voltage across the primary winding. This audio signal is put to use as input for IC LM386. Diodes D2 via D5 connected in bridge configuration constitute a polarity guard to ensure that the amplifier is powered with correct polarity, irrespective of the line polarity, Zener diode D1 might have any breakdown voltage between 6 and 12 volts range.

There’s no require of a separate power switch as the circuit energises (via the generally open contacts of the cradle switch) when one lifts the handset. The circuit may possibly be wired on a general-purpose PCB or by etching a PCB for this circuit. The circuit can be easily tested by connecting a 6 volts supply to line terminals 1 and 2. A hissing sound will be heard from the loudspeaker. Now connect 6V AC from a transformer to terminals 1 and 2 and observe hum inside the loudspeaker. The volume of the hum may be changed through potentiometer VR1. Diodes D6 and D7 limit the input below ? 700 mV. This telephone amplifier is to be connected to the telephone lines in series with the telephone instrument, as shown inside the figure.