Seeking long period timer ideas

[JustinHarlow]

I have an application where I need to pull a signal low for about 1 second every 2 or 3 hours. I want to do it with an absolute minimum of components, since I am going to have to hand-wire and solder 10 or so of these things.

I took a look at the 5555 counter/timer, and it looks as if I could easily hook it up as an asynchronous oscillator and divide the frequency to get the long period I want; I could then use the output to trigger a one-shot (74121 or some such), which would then drive something like a 7406 to pull the line low. This seems simple enough, but it starts to require a lot of wiring when you have three chips plus timing components. I don't want to use a relay, mostly for cost reasons.

By the way, what I am trying to do is automate the timing of a specialized cleaning machine where you manually push a button when you want it to run; the button just pulls a logic input in the system to ground. I don't know exactly how it is wired internally, so just trying to use a TTL output to pull it down will probably screw up the internal levels or blow something out.

Anyone know of a one-shot chip with an open collector output? Anyone know how to wire a 555 to get the long period and short pulse output? Any suggestions or pointers would be greatly appreciated.

 

[Dr_Doggy]

I never believed it when they told me, but micro controllers are amazing!

 

[JustinHarlow]

I never believed it when they told me, but micro controllers are amazing!

True, but it seems rather like overkill to use a microcontroller and write software and all that just to close a switch every couple of hours

 

[Nigel Goodwin]

True, but it seems rather like overkill to use a microcontroller and write software and all that just to close a switch every couple of hours

Not at all, it makes the task trivial - and far more accurate than any 555 based solution (which would require multiple chips).

A simple 8 pin PIC would do the job easily, with hardly any other components required (far less than even a simple 555 timer) - you could even use the smaller 6 pin type, but those are SM only.

 

[Reloadron]

If you are looking at a commercial application and you plan on ten units I would think about a commercial module that can do it all. Something like this from Macromatic maybe. There are other similar units out there from other companies. Here are some others as to commercial application timers. Also I think NTC makes them. Same difference. The idea being the whole mess fits in an 8 or 11 pin socket.

Or a uC but then you are making your boards etc.

Ron

 

[JustinHarlow]

Thanks, chaps. I will have to look at those tiny microcontrollers. I suspect it would be a good investment of my time to learn how to use them for these kinds of tasks.

JEH

 

[Dr_Doggy]

and for this app you only need a few lines of code

 

[MrDEB]

IF you use a bigger microcontroller with more pins then you could use 10 outputs (you stated you need 10 of same on one app) or you need 10 separate timers. If its 10 separate then go with an 8 pin pic. Then you need to program the 10 chips unless someone here can program them for you?
a resistor and a transistor your set to go
Oh yea you need a stable 5v power supply

 

[MikeMl]

Previous thread on similar topic

 

[ericgibbs]

Thanks, chaps. I will have to look at those tiny microcontrollers. I suspect it would be a good investment of my time to learn how to use them for these kinds of tasks.

JEH

hi,
For long time delays the LTC6991 is a single chip solution. ~$2

 

[MrDEB]

good solution Eric!
Linear has lots of stuff that are solutions to lots of electronic ideas etc.