Satellite tuner radio

Encyclopedia of radio electronics and electrical engineering / Телевидение

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If multiple TVs in different rooms are connected to the same satellite receiver (VCR or DVD player), a control problem arises because the IR remote control can only be used in the room where this unit is installed. In this situation, the "radio extender" will help.

In most cases, all information about the operating mode of a satellite tuner, VCR or DVD player is displayed on the TV screen, so in order to control them from a remote room at a distance of several tens of meters, you can use a "radio extender". For its construction, circuitry solutions used in the radio frequency modules of the radio receiver and radio transmitter are used, the description of which can be found in the Radio magazine (S. Petrus. Radio frequency modules. - Radio, 2007, No. 2, pp. 46, 47).

Fig. 1

The device consists of two nodes: the first is an IR signal receiver with a radio transmitter, which converts the IR remote control signals into a radio signal, and the second is a radio signal receiver with an IR emitter, which performs the reverse conversion. The first node is installed next to the TV, and the second - next to the controlled device.

The scheme of the first node is shown in fig. 1. The IR signal receiver is assembled on a specialized TSOP1736 (B1) module, at its output rectangular pulses with logical levels are generated, the duration corresponding to the received bursts of IR radiation pulses from the remote control. These pulses are fed to the base of the transistor VT1, which operates in the key mode and controls the operation of the master oscillator on the transistor VT2 and the output stage on the transistor VT3.

The master oscillator is assembled according to the capacitive three-point scheme, its frequency (433,92 MHz) is stabilized by the ZQ1 SAW resonator.

Fig. 2

When you press the IR remote control buttons, the signals are received by the B1 module and rectangular signals appear at its output. At a low level at the output of module B1, the transistor VT1 opens and the opening voltage pulse through the low-pass filter R2C2R5 enters the base of the transistor VT2 - the master oscillator starts to work. At the same time, this pulse through the diode VD1 and the low-pass filter R4C3R6 enters the base of the transistor VT3, and the collector current will increase, which increases its gain. The amplified signal through the matching circuit C8L3C10 enters the antenna. At a high level at the output of module B1, transistors VT1, VT2 close, the master oscillator stops working and the RF signal does not enter the antenna. This is how a pulsed RF signal is formed, which, in terms of time parameters, is similar to bursts of pulses emitted by the IR to the remote control. Through resistors R3, R4, R6, the bias voltage is supplied to the base of the transistor VT3, and it is constantly in the open state at a collector current of 7 ... 10 mA, this reduces the distortion of the amplified signal. The supply voltage of all stages is stabilized by an integrated voltage regulator on the DA1 chip.

The scheme of the second node is shown in fig. 2. It consists of a super-regenerative stage on a VT1 transistor, an amplifier on an op-amp DA1.1, a comparator on an op-amp DA1.2, a rectangular pulse generator on a DA2 chip, and a key stage on a VT2 transistor. The connection of the super-regenerative stage with the antenna is inductive. The received and detected pulse signal from the emitter of the transistor VT1 through the low-pass filter R4C6 is fed to the input of the amplifier and, after amplification, to the input of the comparator. The output signal of the comparator controls the operation of the pulse generator. The supply voltage is stabilized by the voltage regulator DA3.

Fig. 3

When a transmitter signal is received at the input of the super-regenerative stage, a high level will appear at the output of the comparator and the pulse generator on the microcircuit will start working. Pulses with a repetition rate of about 36 kHz through the resistor R17 are fed to the base of the transistor VT2, the pulsed current flows through the IR emitting diode VD1 and the HL1 LED, which shines. If there is no signal at the input of the super-regenerative stage, the output of the comparator is low, the pulse generator does not work and the transistor VT2 is closed. This is how pulses of IR radiation are formed, which are similar in structure to pulses of IR remote control. They arrive at the IR receiver of the controlled equipment (tuner, VCR, etc.).

The device mainly uses surface-mounted parts: resistors P1-12 of size 0805 or 1206, capacitors - K10-17v or similar imported ones. All coils are frameless and wound on a mandrel with a diameter of 3 mm. In the radio transmitter, they contain 5 turns of wire PEV-2 0,35 each, with L1 and L2 wound turn to turn, and L3 - in increments of 0,7 ... 1 mm. In the super-regenerative cascade, coils L1, L2 are wound with PEV-2 0,67 wire and contain 10 and 2,5 turns, respectively, they are placed close to each other on the board, coil L3 is wound with PEV-2 0,2 wire, contains 30 turns and for strength filled with a small amount of hot melt adhesive. The antenna is a piece of wire PEV-2 0,67 about 16 cm long.

All parts are mounted on one side of printed circuit boards made of two-sided foil fiberglass 1 mm thick. A drawing of the IR receiver board with a radio transmitter is shown in fig. 3, and the radio receiver boards with an IR emitter - in fig. 4. The foil on one side is completely left (except for the areas around the holes for the outputs of the TSOP1736 IR module, 78L05, NE555N microcircuits, 2SC2712 transistor) and is used as a common wire. Through the remaining holes, the metallized surfaces of the sides are connected by pieces of tinned wire. The boards are placed in suitably sized cases with holes for the IR module, emitting diode and antennas. To power the nodes, you can use network power supplies with an output voltage of 7 ... 9 V and a current of up to 100 mA.

Establishing a transmitter node with an IR receiver consists in tuning the antenna circuit by compressing or stretching the turns of the L3 coil to the maximum of the emitted signal. It can be monitored with a simple field strength indicator, or a radio receiver assembly can be used by removing it some distance away. In the process of establishing the IR module, it is necessary to irradiate with pulses from the remote control.

Fig. 4

Tuning the radio receiver assembly with an IR emitter to the transmitter frequency is done by compressing or expanding the turns of the L1 loop coil until maximum sensitivity is obtained. During the setup process, it is convenient to control the received signal at the output of the op-amp DA1.1 by connecting an ultrasonic frequency converter with headphones or a loudspeaker to it. If the glow of the control LED HL1 is observed after the radio transmitter stops working, you should select the resistor R11 so that the LED goes out immediately after the radio transmitter stops working.

To control one device from several rooms, you should install an IR receiver unit with a radio transmitter in each of them, or make such a unit mobile and carry it with you. Moreover, it is located within the range of the IR remote control. A radio receiver with an IR emitter is placed next to the controlled device so that the IR emitting diode "irradiates" the front panel of this device.

Author: S. Petrus, Kremenchug, Ukraine; Publication: radioradar.net

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