IR burglar

The 555 in the transmitter section generates pulses that cause the IR LED to "flash" at a certain frequency.

In the receiver section, the IR receiver picks up these pulses. The 4538 is a monostable, meaning it goes high for a period of time when it receives an input signal, then goes low when the signal is absent for that amount of time.

So, when the beam is unbroken, the pulses keep the 4538 "on", which disables the siren circuit (the 3561). When a "burglar" breaks the beam, the 4538 will stop receiving pulses, and time out, enabling the siren.

When the beam is unbroken again, the siren will stop.

thank you for your reply.

i wanna some information about IC CD4538 .. how to work?

when LED2 is on?

**broken link removed**

The source of the circuit, good description of how it works... The EFY website requires your Email address to register, not sure if the link will work otherwise. I registered years ago, no spam or an mail for that matter. It's an electronics magazine from India, in English, lots of good stuff there.