Timer Question

I want something I can _trigger_, preferably _retriggerable_, off the shelf. I could do my own, but I'm lazy ;-) ...Jim Thompson

You'll also need a socket..

Jamie

This is a classic industrial control component, there are thousands of variations. The retriggerable thing constrains the number of modules that will work for this case, but I'm pretty sure that many of the modules have such an option.

Jon

Start with something like this for $5.00:

Ed

How do you _retrigger_ a mechanical timer ?:-) ...Jim Thompson

You can buy them. I'd start with Panasonic- they're cheaper than omron, and usually less complex to deal with.

their support is complete garbage though, not that you'd need it for a timer. Keep in mind that programming the digitals ones can be infuriating and involves map folded, poorly translated, japanese sofware logic with bonus 7 other irrelevant dead languages datasheets.

here's the start page

If accuracy is not critical, the versions with dial are easy.

these things tend to be cheapest off ebay of all places. Grainger will take you for a serious ride if you go that route.

Everyone is missing that key word "trigger". I need to hit it with a pulse and have it run for X-hours, then reset... and wait for the next trigger.... maybe just a pile of 74HC283's ...Jim Thompson

yes, you can trigger any of these, they're fully electronic- even the ones with the clear knob.

Give its knob another twist.

Not many 'retriggerable' ones there. Roll your own, 1sec oscilliator fed into a couple of 4017's? I have a simple one that does 2 4 &8 hrs.

Cheers

If you are happy writing a bit of software, one of the really tiny micros will do whatever you want in this area.

PICs and AVRs come in 8 pin packages with a reasonably good internal clock so one chip is all you need. No xtal, no Rs and Cs for timing...

A flip flop and a one shot:

Modify it to stop after 24 hours. Your roll your own trigger circuit (FF + triac, relay, whatever) latches on, but you'll need to add something mechanical to the appliance timer to reset your circuit when the timer reaches 24 on the dial. Functional diagram:

----------- input pulse---|Jim circuit| ----- | | |Timer|---timer ac out---relay AC in---|ACin ACout|------| | | | | |---+ ----------- ----- | | | +---------Reset--------+

Input pulse to flip flop, one shot to reset it comes to mind, but I'll call it your circuit as it will include more than a flip flop.

The input pulse turns your circuit on, which sends ac to the timer, starting it. After the timer has produced AC out to the relay for the amount of time you set, it drops timer ac out, but keeps turning, because your circuit has not been reset.

If you can mod the timer to trigger a one shot when the dial hits 24 to produce a reset signal to turn your circuit off, that will leave the timer at 24, awaiting the next trigger pulse.

Your original post mentioned a duration of up to 23 hours, implying an interval between trigger pulses of greater than one day. If that interval is less than a day or you can't mod the timer, then this approach is no good for you.

Ed