Why using 555 timer in ir transmitter?

Answer 1

The 555 is a timer and oscillator chip capable of sourcing and sinking 200 milliamperes, and is useful for pulsing an infrared LED to power an infrared transmitter. It can be pulse width modulated or otherwise controlled via the various control pins.

See: http://talkingelectronics.com/FreeProjects/555/555-P3.html

in most cases the IR detector used is TSOP sensors which works only on a specified frequency of 38KHz. So by using 555 timer, we can design the circuit very easly to work @ 38KHz. dats why in 555 is used in many IR txns.

Answer 2

Hi Everyone

Ir receiver works as Band bass filters centered at f0 (Carrier frequency), so you should send pulses of IR transmitter LED at the carrier frequency. 555 timer IC can easily generate the carrier frequency by adjusting it to work in Astable mode. Adjusting R1 & R2 and value of capacitor can easily generate the desired frequency.

Note: In case of no IR signal sent or continuous transmission, the output of IR receiver is high. during cut-beam the IR signal, the output of IR receiver still high then removing the obstacle the IR signal at f0 sent again. The receiver output will be low then after short time the output back to high state

best wishes

Islam