32 Channel IR Remote Controller by SL490

Figure 1 

This is a 32 channel infrared remote controller circuit fundamentally includes key pad, decoder, transducer stage, an output and a battery. Circuit is like a pocket calculator in size. Commands are formed by using 8 × 4 matrix with 32 switches.

Be aware that only one switch functions at one time and during one command is been generating, input circuitry is irresponsive to the other commands.

Every key pad button generates 5 bit binary code and IC1 sends this code to the IR leds through D1 and D2 diodes. Code is shaped from 6 pulses with 5 gaps. Pulse position modulation – PPM technique is used for transferring data. Data information occurs at gaps. For logic 0, long gap, for logic 1 short gap is generated

Pulse and gap lengths are calibrated by using P1 potentiometer.

Length ratio between logic 0 and logic 1 is (1.5 / 1). Pulse length between two 54ms code word is about 3ms.

Transmitter transmits infrared light only when IC1’s 3 numbered pin is high.

SL490 includes an auto stand-by circuitry. When the buttons are not used for a while, IC will swich to stand-by mode and stand-by current will be 6uA.