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Analog Timer Circuit


#1

I have a little project I’d like to build this weekend that requires an analog circuit to simply create a 25-30 min delay before lighting an LED. Does anyone have a circuit available that will do this using just common components that I might already have (resistors, capacitors, etc.). Since the analog components are part of the visual appeal of the project, I want to avoid any chips if possible. I might could accept a 555 if necessary. The ones I’ve found so far are going to require ordering parts which I can’t get quickly. Thanks for any ideas.


#2

Maybe http://clarkson-uk.com/555-timer/operation/frames3.html


#3

@ Farsa - thanks for that. It looks like that site will not let you enter more than a three digit number for the seconds. I’m sure I can figure out how they’re calculating the R & C values to determine the circuit for 1500 sec.


#4

Just use the formula it gives

t1(secs)=1.1RaC/1000

you can use their calculator for 750 secs and multiply by 2 either Ra or C in any of the possible combinations, just make sure you test it :smiley:

ps.:they advise “For reliable operation, Ra must not be larger than 10M.”


#5

Ah, didn’t see that up there. I’ll play around and see what I can get to work.

If anyone else has other solutions, I’m still interested. A big part of this project is showing of analog components. So, the more parts the merrier :slight_smile: