16 channels with only 5 ICs

10-40 — elektor october 1982 16 channels with only five ICs Figure 1 illustrates the circuit diagram of the transmitter. It contains; a key- board with 16 on and off keys, the transmitting IC, and final stage. A 9 V battery such as the PP3 is ideal for the supply. A command given by depressing a key is immediately converted into a corre- sponding E-D-C-B-A 5-bit binary code. We have purposely left the detailed explanation of how the code is allocated till later, as any reference to it as this stage could confuse the issue. The 5 bit code, which is nothing more than a pulse sequence of 6 identical signals, is transmitted by modulating the infra-red diodes D1 and D2. The actual information, is hidden in the operational switch, ensuring that the power consumption does not exceed 6 /../A, when the circuit is in a stand-by situation. Any even number of keys can be used as long as they do not exceed 32. This is because an "off" as well as an "on" key is required for each function. The...