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Time delay circuit

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grosey

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I think i got the answer

i am only 14 but i do a engineering diploma and currently doing alot on time delays at the moment :L got a 2 day exam next week on them so:

On the top rial, first parallel line, put a variable resistor followed by an electrolytic capacitor, then a push to make switch. In between the variable resistor and electro capacitor, have a rail going to the right with a resistor then 2 transistors ( Darlington pair ). On the second parallel line put your output, in this case a loudspeaker or buzzer etc. On the top rail have a open close switch to rest the time delay.

I created my own time delay for boiling eggs for 5 mins etc on a comp program, basically when you push the push to make switch the electro capacitor builds up for 5 minutes ( what i set it to in farads) and then it releases it all making the voltage less than 0.7 above it , in between itself and the variable resistor therefore turning the loud speak on.

You can adjust this to your fire alarm hopefully.

Hope this helps :)
 
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