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INFRARED_ALARM_TRANSMITTER

2016-04-07 06:46  
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INFRARED_ALARM_TRANSMITTER
The circuit diagram for the infrared transmitter appears in this figure. The oscillator uses IC1 as a relaxation oscillator. Capacitor C2 and resistor R4 are the timing components, and they are connected between the output of IC1 and its inverting input (pin 2). A roughly square-wave signal is generated at pin 6, the output of IC1. This signal is used to drive infrared LED D1, via emitter-follower buffer-stage transistor TR1 and current-limiter resistor R5. The specified value for R5 sets the LED current at nearly 100 mA, but as the LED is switched off for about 50 percent of the time, the average LED current is a little under 50 mA. This is the maximum acceptable drive current for most normal infrared LEDs.