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TX-2B forms the main part of the circuit. The push-button switches from S1 to S5 are used to activate (on / off) the corresponding O / P channels in the receiver / decoder circuit. These pushbutton switches are connected to the TX-2B's built-in latch circuit. Resistor R7 determines the frequency of the internal TX-2B oscillator. Resistor R1 and Zener diode D1 form a simple Zener regulator circuit to supply a 3V IC from 9V mains supply. C2 is the filter capacitor while C1 is the noise-pass capacitor. D2 is a power LED while R6 limits the current through the same LED. S1 is the on / off switch. The coded control signal will be available at pin 8 of the IC. The coded signal available at pin 8 without the carrier frequency. This signal is fed to the next stage of the circuit which is a radio transmitter. Crystal X1 defines the frequency of the oscillator for the transmitter section. R2 is the bias resistor for Q1 while R3 limits collector current Q1. The encoded signal is coupled to the Q1 to C3 complex for modulation. The Q2 transistor and associated components provide further amplification for the modulated signal.
Remote receiver / set-top box.
- This circuit can be assembled on a Ferro board or PCB.
- Use 9V DC to power the transmitter / receiver circuits.
- The battery is the best choice for operating the transmitter / receiver circuit.
- If you are using a DC power supply, it should be well-organized and free from any kind of noise.
- Both stages must be mounted on stands.
- Relay for RX-2B output.
- The method for attaching the relay to the RX-2B output is shown below. When the push switch S1 of the transmission circuit is pressed, pin O / P1 (Pin 7 on RX-2B) will rise. This makes the 2N2222 transistor turn on and the relay energized. The same technology can be applied to the other output pins of the RX-2B. The relay used here is 200 ohm type and with 9V supply voltage the load current will be 45mA which is good for 2N2222 whose maximum possible collector current is 900mA. When using relays of other ratings, this point must be remembered and not to use a relay that consumes current greater than the maximum potential collector current of the armature transistor.
