Logic-Triggered 555 Needed

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captainkirksdog

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555 timer long delays

Hello,
I need a circuit that shows how to trigger a 555 from a CMOS-level logic source. The 555 must have a 1-hour delay and then a 1-minute alarm. Does anyone have anything like this? Thank you.

<ckd>
 

7eantoon/gadgets/555/555.html

Hi captainkirksdog,

You don't have to worry about triggering a 555 from a CMOS-level logic source as long as you use a CMOS 555 variant, which in fact is a must if you want such long delays: 1-hour.
With standard 250 nA BIAS input currents you won't be able to acquire 1 hour delay without special circuits and PCB layout.
Read this nice tutorial about 555 timer:
**broken link removed**
 

tiggered 555

1 hour is really too long for a 555 timer, an RC of 3600 seconds even with a 1M ohm resistor needs a 3600 microfarad capacitor, which would probably be to leaky to ever charge with a microamp.

So you are going to need to use a counter to divide the output frequency down and some of the ripple counters have a built in oscillator, so you really need a 555?
 

now i remember where i saw it, a 555 timer with a 24 stage binary counter, from phillips, information at --> **broken link removed**
 

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