Laser alarm circuit help

Thread Starter

Noj123

Joined Apr 14, 2015
3
Hi all

I need to build a laser security circuit for a school project and was wondering if it would be possible to add a exit delay to my circuit so that there would be around 20 seconds to leave the room without triggering the alarm.

This is the circuit i have come up with so far... sorry i am a bit of a noob when it comes to electronics and any help would be much appreciated.

laser circuit2.png

Thanks
 

Bernard

Joined Aug 7, 2008
5,788
Try connecting a 555 timer output, pin 3 via diode, k to 3, anode to 400 ohm. One meg R from Vcc to pin2, & 20 uF gnd. to pin 2, 10k ohm Vcc to pin 4 ,reset. On power-up ckt will be hot, with SW pin 4 to gnd. pressing SW will reset 555 for 20 sec, disabling laser from opening 400 ohm ckt.??
 

Thread Starter

Noj123

Joined Apr 14, 2015
3
Thanks for your reply. I am a bit unaware of the 555 timer.. is this how it should look? i am not sure where i should actually include this in my current circuit and where i should connect the output of pin 3 to.

555 timer circuit.png
Thanks
 
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