Electronics > Beginners
A simple circuit to trigger relay for 30 seconds
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sairfan1:
I have been deveoped some small projects using mcu, but this time i want a low cost wihtout mcu solution with this thought it will help me to learn electronics.  as I'm not good in totally electronics based solution so need help.

I have a 12v 0.6A relay to lock a door, when i press a button it will activate the relay for 30 seconds and then it will release the relay again.  I would like to have pot to increase or decrease little bit of time.

I have a little idea that i would need some transistors to turn relay on probabally BD series, some diaod and may be capacitor to hold relay for some time, some other approach could be using 555 timer.

Please advise whatever apprache you think is bettter.

thanking you,
SeanB:
30s is fine, just you will be using an electrolytic capacitor for timing, and thus it will be less than accurate. Otherwise a CMOS NAND gate as oscillator and a ripple counter, with the other 2 NAND gates making a RS flip flop, will do this well.
drussell:
This is one of the classic use cases for a 555 timer.

That would be my suggestion for the most straightforward solution.
JS:
I'd porbably use an 8 pin uC... Sorry.

JS

sairfan1:
why your praference would be uC, to save time? i believe using capacitor charge will be lowest cast but not sure how reliable it would be.
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