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HI Guy's

My application is this.
At the momentary press of a button I would like to activate a relay
That would start the culvert unloader for 15 seconds. After that a second
relay would start the loader for 15 seconds.

It may sound kind of lame, but I plan to use it at shows where the
little engineers can operate the culvert accessory without any supervision.

I can do this with a mechanical timer and a couple relays but it's kind
of bulky. So solid state would be a better solution.

I was thinking of a 556 timer circuit, but I don't quite understand all
the jargon. Stable,monostable ect.
I'm also not sure about the reset function..

Can anyone help ?


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I do not do much at the chip level any more. Can be done with a combination of modular Mars timers and relays. Numerous uses of modules with relays are here.

Power source is 18 volts from a transformer to run timers and relays.

Not sure of the sequence of events you want,if you want the first one to shut off after the second one starts. I would have to think about it and draw up something but I think it can be done.. You have to be a little more specific as to the 2 events.

You are looking at maybe $40 for the parts.

Dale H
Thanks to all for the help.
Sure Gary, send the PIC.

A good friend of mine sent me here:


with a little modification this should work.

I'll be a little more specific.

When the young engineer pushes the button.
The unloader starts and runs for 10 to 15 seconds.
Then stops.
Then the Loader starts, runs for 10 to 15 seconds, then stops.

I have a mechanical timer and relays that will work, but they are
24V and just to bulky to do the job. In a pinch I'll use them.
Something solid state could be hidden in a small building and be setup
and moved a lot faster....

Thanks again for all the help guy's..

Are you assuming a PIC is a picture? I was referring to a Programmable Computer chip. Here's a quik description I posted the other day.

Posted January 19, 2012 01:50 PM Hide Post
All my designs use PICs. For those not familiar with it a PIC is a complete computer on a chip, ie; processor, memory, I/O. For this circuit I used a Microchip 12F508. It's an 8 pin DIP that costs 50 cents. Microchip now has a cheaper one the 10F200 for 30 cents. So basically you write some software to do what you want. In this case read the ambient level and use that as normal level. Adding some filtering and some hold delay is just a few more lines of code.
2 of these circuits would work also using these 12 volt DC timer modules.. The events can be independent with 2 pushbuttons or sequenced with one push button. The latter would require 2, DPDT relays instead of the SPDT relay used in the linked post. The 1 meg pots make it adjustable up to 180 seconds after the button is pushed. No messing with formulas or IC chips or PC boards.

Dale H
Originally posted by Gary E:

If you really would like total solid state I can give you PIC to do that function.

Wow! Are you offering to write the code and send him a programmed part? And by total solid-state are you having the PIC drive triacs (instead of relays) for AC switching?

If size matters, and you're willing to do some assembly, then a PIC with a handful of external parts would be the most compact solution. All parts would fit on a board, say, 1" on a side if total solid-state, and maybe 2" on a side if relays.

Something to double-check before committing to a specific component-level timing circuit are the start-up and "don't do that" cases. Some timer circuits immediately start a cycle when first turned on. Probably a don't care. Can the loader and unloader run at the same time? Maybe your power supply is limited and doesn't like that. Is it OK for a new Load cycle to start if the kid presses the button while the Unload cycle is still running?

Not trying to over-complicate matters but whether using modules, discrete components, or a PIC, I think measure-twice, cut-once applies here.
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