Infra-red remote control - the transmitter

A remote control system having 20 channels with analogue functions can only be realised with the use of special ICs. Any other method would require an enormous quantity of components. However, it is all very easy, thanks to Plessey who produce a range of ICs designed specifically for this purpose. Our designers selected three of these for the remote control system here. It is capable of transmitting no less than 32 com- mands when used in conjuction with the receiver and associated circuits. The transmitter basically consists of a keyboard decoder IC, an output and transducer stage and a small battery. In much the same manner as a pocket calculator, the commands ordered by the keyboard are fed into a matrix. This is arranged in 4 columns and 8 rows enabling 32 keys to be used (32 junctions or cross-points). but is available from the data source mentioned at the end of the article. The 5 bit code is transmitted by means of the infra-red transducer diodes D1 and D2. The code is in t...