Infrared Remote Control circuit

Posted on Oct 20, 2012

The transmitter is shown and although straightforward, there are a couple of tricks that I had to incorporate to minimise battery drain during standby. Although the PIC quiescent current is only 200uA, that will still flatten a pair of AA or AAA 1.5V cells over time. The receiver provides motor drive (forward and reverse) for the motorised pot, and a relay for muting. The relay simply shorts out the preamp's output - this will not cause any damage to the preamp, as long as the relay contacts are connected directly to the output socket. When the circuit is powered on, there is an automatic mute for 10 seconds, but this may be disabled if you don't want it.

Infrared Remote Control circuit
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Infrared Remote Control circuit - image 1
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The board is designed to use a relay having a 5V coil, but other relay voltages can be used if desired - note that D1 must be omitted from the board if you use a higher voltage relay. The diode must be connected in parallel with the relay coil, but will have to be mounted off the PCB. Make sure that you size the LED series resistor properly for the voltage you use - 2.2k as shown (with the 5V supply) will not give a bright glow, but this is intentional. You may wish to experiment to get the effect you want. To use a different relay voltage, simply disconnect the relay return from the 5V point, and connect to a suitable source voltage for the relay (remember to remove D1 from the board and mount it externally, in parallel with the relay coil. Please note that C6 is not mounted on the PCB. This cap must be a bipolar (non-polarised) electrolytic, and it should be mounted directly to the motor terminals with the shortest possible leads to prevent motor noise from causing interference. You may use a smaller cap (100nF ceramic, for example), but to keep noise to the minimum I suggest the value shown. Q1, Q2, Q4 and Q5 form a full-bridge motor drive circuit. When Q1 conducts, its collector will pull low, providing base current to Q5, which also turns on. This provides positive voltage on the M2 lead and negative on M1. Q2 and Q4 are switched on in the same way. The IC is programmed so that it cannot turn on Q1 and Q2...

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