TX-2B / RX / 2B 5 channel radio remote control.
This article is about a simple 5 channel
radio remote control circuit based on ICs TX-2B and RX-2B from Silan
Semiconductors. TX-2B / RX-2B is a remote encoder decoder pair that can
be used for remote control applications. TX-2B / RX-2B has five
channels, wide operating voltage range (from 1.5V to 5V), low stand by
current (around 10uA), low operating current (2mA), auto power off
function and requires few external components. The TX-2B / RX-2B was
originally designed for remote toy car applications, but they can be
used for any kind of remote switching application.
Circuit diagrams and description.
Remote encoder / transmitter circuit.
5 channel redio remote control encoder / transmitter circuit
The TX-2B forms the main part of the
circuit. Push button switches S1 to S5 are used for activating (ON/OFF)
the corresponding O/P channels in the receiver / decoder circuit. These
push button switches are interfaced to the built-in latch circuitry of
the TX-2B. Resistor R7 sets the frequency of the TX-2B’s internal
oscillator. Resistor R1 and Zener diode D1 forms a simple Zener
regulator circuit for providing the IC with 3V from the 9V main supply.
C2 is the filter capacitor while C1 is a noise by-pass capacitor. D2 is
the power on indicator LED while R6 limits the current through the same
LED. S1 is the ON/OFF switch. The encoded control signal will be
available at pin 8 of the IC. The encoded signal available at pin 8 is
without carrier frequency. This signal is fed to the next stage of the
circuit which is a radio transmitter. Crystal X1 sets the oscillator
frequency of the transmitter section. R2 is the biasing resistor for Q1
while R3 limits the collector current of Q1. The encoded signal is
coupled to the collector of Q1 through C3 for modulation. Transistor Q2
and associated components provide further amplification to the modulated
signal.
Remote receiver / decoder circuit.
5 channel radio remote decoder
5 channel radio remote decoder
The remote receiver circuit is built
around the IC RX-2B. The first part of the circuit is a radio receiver
built around transistor Q1. The received signal is demodulated and fed
to pin 14 of the IC. Pin 14 is the input of the built in inverter inside
the IC. R2 sets the frequency of the IC’s internal oscillator. O/P 1 to
O/5 are the output pins that are activated corresponding to the push
buttons S1 to S5. Zener diode D1 and resistor R12 forms an elementary
Zener regulator for supplying the RX-2B with 3V from the 9V main supply.
C12 is the filter capacitor while R11 is the current limiter for the
radio receiver section. Diode D2 protects the circuit from accidental
polarity reversals. C15 is another filter capacitor and C14 is a noise
by-pass capacitor.
Notes.
- This circuit can be assembled on a vero board or a PCB.
- Use 9V DC for powering the transmitter / receiver circuits.
- Battery is the better option for powering the transmitter / receiver circuit.
- If you are using a DC power supply circuit, it must be well regulated and free from any sort of noise.
- Both ICs must be mounted on holders.
Interfacing relay to the RX-2B output.
The method for interfacing a relay to
the output of RX-2B is shown below. When push button switch S1 of the
transmitter circuit is pressed, pin O/P1 (pin 7 of the RX-2B) goes high.
This makes the transistor 2N2222 to conduct and the relay is activated.
The same technique can be applied to other output pins of the RX-2B.
The relay used here is a 200 ohm type and at 9V supply voltage the load
current will be 45mA which is fine for 2N2222 whose maximum possible
collector current is 900mA. When using relays of other ratings this
point has to be remembered and do not use a relay that consumes a
current more than the maximum possible collector current of the driver
transistor.
Interfacing relay to the remote decoder
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