555 monostable triggering problem

Thread Starter

skj

Joined May 20, 2010
22
This is a circuit to alert housemates that some one has opened the gate without using door bell.I have used 555 IC in Monostable Mode.To prevent permanent high at output pin3 I used a RC combination to trigger pin2 for a short time which times out approx 3 sec pulse at pin3 activating a relay and in turn a bell.
I am attaching the circuit (monostable circuit and relay at pin3 not shown).Timings are not critical.

My problem is that if I directly connect RC out to pin 2 of 555 nothing happens
therefore I Used buffer stage using Nand Gate ,transistor and relay.Circuit is perfectly working now.

I don't know much calculations and have only workable knowledge of electronics.

Please indicate flaws in the circuit, your suggestions are welcome.
 

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Thread Starter

skj

Joined May 20, 2010
22
Thanks for your comments,I have read your very useful article I will do the changes in my circuit and will come back if any query arises.
 
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