DIY radio circuit for wireless headphones. How to turn any headphones into wireless ones. Setting up wireless headphones for your TV

This article provides a diagram of an IR receiver and IR transmitter for a TV, which allows you to watch television programs on headphones without disturbing others.

In Fig. 1 shows electric wireless headphones circuit, operating in the IR range. It is a two-stage amplifier. The DC amplifier mode is activated automatically due to the DC feedback through the resistance chain R3, R4. Capacitance C3 turns off the AC OOS. From 8 to 10 IR diodes are connected to the collector circuit VT1.

In the absence of an acoustic signal, a quiescent current flows through the IR diodes - approximately 40...50 mA. When an acoustic signal arrives, the current through the diodes will change, and therefore their radiation will change.

Transmitter parts

Containers - K50-6, K50-35 or similar from a foreign manufacturer. Transistors VT1 - KT312, KT315, KT3102 with any letter indices, VT2 - KT817, KT815 with any letters, IR diodes - AL107A, B. Trimmer resistance - SPZ-19a.

The setting consists of setting the quiescent current through the IR diodes by selecting resistance R5. Resistance R1 is set to max. modulation depth (at the maximum audio signal at the input), at which there is no distortion.

The receiver can be built according to the circuit shown in Fig. 3. It uses a special audio amplifier chip DA1 with a photodetector (infrared photodiode) BL1 connected to its input. The receiver is powered by a 3 V battery.

IR radiation from the transmitter enters the photodiode of the receiver and forms an audio voltage, which is then amplified by an ultrasonic chip. Headphones with a resistance of more than 50 Ohms are connected to the output of the microcircuit. The volume setting is selected by changing resistance R1.

I present to you a diagram of wireless headphones using IR rays (infrared rays)

Somehow I needed wireless headphones to watch TV. Otherwise, the child is sleeping, you can’t make it loud, and I can’t read lips.
Prices in stores are generally tolerable, but I didn’t dare to buy, I decided to make it myself.
And so, the essence is this: the sound signal from the TV is transmitted through IR diodes and received by a photodiode in the receiver to which the headphones are connected.
Here's a diagram of it all:

Transmitter

The transmitter does not contain scarce parts; IR diodes can be taken from simple remote controls for household appliances. The board can be assembled using surface mounting.

Receiver:

I installed ceramic capacitors C1 and C2, but it is better to install film capacitors (the sound will be cleaner).
I placed all the boards in the case:

The transmitter itself

The red LED serves as a power indicator.

And the receiver:

Instead of simple batteries, I placed batteries from a children's car at 3.7 V 500 mA in the receiver body, very convenient to charge.

During the tests, in principle, everything suited me, the main thing was that the transmitter and receiver were in the same plane. The sound quality is quite good for such a simple circuit.
The first performance tests were carried out using an FM receiver.

Below is the test video

Probably, everyone in life has had a lot of moments when they want to watch a movie in full sound in the evening or at night, but relatives and neighbors are unlikely to approve of this idea, and you have to be content with a muted mode and strain your ears. You won't get much pleasure from watching this. Therefore, it makes sense to purchase headphones with a long cord or with remote signal transmission. The latter option is preferable, since there is nothing superfluous; wires are not always a normal option for complete immersion in a movie or concert.

If wireless headphones are too expensive, there is a budget option, which is exactly what is presented in our article.

The photo shows the device in the housing and the assembled transmitter board.

For those who are comfortable with a soldering iron - homemade wireless headphones using IR (infrared) rays. In more detail, this is an IR signal transmitter and, accordingly, a receiver for headphones. The operation of this device is logical and understandable to anyone, even a novice radio amateur. The transmitter connects to TVs via an audio output; of course, you can use any sound source on any other equipment. The transmitter contains IR diodes, exactly the same as those found in television remote controls; the transmitter converts the sound from the TV into an infrared signal, which is received by the receiver.

So, in order to assemble such a headphone attachment that turns them into infrared headphones, you need this circuit.

The circuit contains a small number of parts; soldering it will be easy. You can even limit yourself to wall-mounted installation. The voltage supplied to the transmitter is 12 Volts. If it is less than, say, 9 volts, then there will be noise. There is no need to configure the transmitter in any way; it is simply connected according to the diagram. Above you can see it on the board in the assembly.

The diagram shows four infrared diodes for signal transmission, but in the actual assembly the author installed only three diodes, since they were not available. Theoretically, you can leave even one, but the signal will be better received if there are a large number of them. Connecting infrared diodes in the photo.

The basic part of the receiver is the TDA 2822 chip. Its cost is very low.

Voltage to the receiver with a nominal value of 3-4.5 Volts is supplied from any source.
Its board is quite compact.

The entire electronic assembly of the receiver fits into a suitable box

All that remains is to select a power source. A battery from a children's toy was used for this purpose. As a result, it was possible to charge the battery from time to time, eliminating the need to buy batteries.

Everything fits into a well-chosen case

When everything is assembled, all that remains is to check the signal receiver. We turn it on, headphones, point the TV remote at it and press any button. If you hear clicks in the headphones, then the receiver is functioning.

See how homemade IR headphones show up in action.

In order not to deprive those around you of comfort with loud sound while watching TV or listening to an audiobook on the computer, use homemade circuits to broadcast sound and receive it with wireless headphones. The device operates in the infrared range. By adding amplitude modulation to the design, you can easily implement a simple version of wireless headphones for your TV with your own hands.

Transmitter circuit works in the IR range. It contains a two-stage amplifier operating in mode A. Due to the OOS chains added to the amplifier circuit through resistances R3 and R5, the DC amplification mode will work automatically.

Capacitance C3 is designed to eliminate negative feedback arising from alternating current. Four infrared LEDs are connected to the collector circuit of the second transistor VT2. While there is no input signal at the transmitter input of the wireless headphones, a small current flows through the IR LEDs. As the sound signal at the input increases, the current flowing through the LEDs will change and their infrared radiation will be modulated.

The wireless headphone transmitter circuit is powered from a low-power 12V power supply. The transmitter is turned on by switching toggle switch SA1. The transmitter input is connected to the linear output of the TV. The amplitude modulation depth is adjusted using resistance R1.

IN receiver circuit The headphones use the ULF chip KR174UN23 in its standard inclusion. An infrared photodiode is connected to the input of this microcircuit. When IR radiation from a wireless headphone transmitter is received on it, a signal is formed that is amplified by a ULF chip.

Regular headphones are connected to the amplifier output. Using variable resistance R1, the sound volume is adjusted.

In this case, to transmit a stereo signal, no encoding or decoding is carried out; transmission is carried out on two spaced frequency channels, each for its own stereo channel, using two transmitters identical in design, but different in carrier frequency. Reception is carried out on two equally identical receivers tuned to different frequencies.

The schematic diagram of one transmitter channel is shown in Figure 1. It operates in the range of 64-73 MHz or 88-108 MHz (for different channels). The scheme is simplified to a greater extent by the fact that for remote headphones a range of more than 10-15 meters is not required. Therefore, the transmitter is single-transistor with a minimum supply voltage.

Modulation is carried out by a low-frequency signal taken from the linear output of the tape recorder (or other equipment). The low-frequency signal arrives at the base of the generator at VT1 and affects its operating point, which in turn causes a change in the capacitance of its transition, which inevitably affects the tuning frequency of the circuit. This produces mixed AM-FM modulation (since changing the bias voltage also changes the signal level), but the AM component is effectively suppressed by the receiver's limiting amplifier.

Figure 2

Schematic diagram of the receiver (one of the channels) in Figure 2. The FM radio receiving path itself is assembled on a KHF058 microassembly. which contains a complete FM path containing an amplifier, a mixer, a local oscillator, an amplifier and a preliminary ULF. The IF value is low, about 70 kHz, as a result of which the role of the FSS is performed by the active RC filter present in the chip.

In addition, such a low IF makes it possible to eliminate the need for an input circuit, since the superheterodyne behaves as a direct conversion receiver with respect to the mirror channel at a bandwidth of about 50 kHz.

As a result, the tuning frequency of the receiver is determined by only one heterodyne circuit, which can be adjusted by resistor R4, which changes the voltage on the varicap VD1 (adjustment is necessary, since there is no quartz stabilization, and the transmitter and receiver are affected by external factors, such as temperature, changes in the voltage of the power source, external containers).

From the output of the low-frequency detector, the signal goes through the R7 volume control to the UMZCH, made on the K174XA10 microcircuit. This microcircuit has a complete AM receiver path, including a very high-quality ultrasonic frequency, but since it was not possible to find a microcircuit that has only such an ultrasonic frequency, this one is used partially (its AM radio path is not connected).

Figure 3

The transmitter is mounted on two identical printed circuit boards (Figure 3), one for each channel, and placed in a cylindrical plastic case with a connector located at the end. Both channels are powered by one element type A316 (or “AA”). Two wire pins, each 30 cm long, are used as antennas; they are directed in different directions.

Transmitter coils for the 64-73 MHz range contain L1-14 and L2 -10 turns, for 88-108 MHz, 8 and 6 turns, respectively. The coils are frameless, wound on M3 screws, which are removed from them after processing the leads. Wire PEV-0.31. The receiving paths are also mounted on separate boards (Figure 4), but the design of the receiver itself is highly dependent on the design of the headphones.

If they are large, TDS16 type boards can be placed in their cases, and the power source can also be placed there (three “AAA” cells or four disk batteries of type D-0.25). If the headphones are small, you may need to place the power source in a separate case connected to them by a wire, or place the entire two-channel receiver in a separate case

Figure 4

The receivers differ only in the L1 coils; their design is the same as that of the transmitter coils. This coil contains 8 turns for the 64-73 MHz range or 5 turns for 88-108 MHz. The setup comes down to pairing frequencies.

To do this, you need to turn on both receivers and tune them to the free sections of their ranges by shifting and spreading the turns of their coils (with R4 in the middle position), and then by shifting and pushing apart the turns of the transmitter coils, tune the transmitters to these frequencies.

To improve the matching of transmitters with a specific nominal output signal of the equipment, it is necessary to install potentiometers at the inputs of the transmitters, between connector X1 and capacitors C1.