Owain mentioned timers in an earlier thread, and I need a special kind of timer that switches ON for just twenty seconds, then OFF for ten minutes.
Anything like that commercially? Or do I have to consider using the PC or a dedicated hardware circuit using a 555 timer chip? I could also use a BASIC Stamp and a relay, probably.
But the must surely be something like this on the market already, I should have thought.
The times should be variable. That is, the ON time might vary between
3 seconds and 90 seconds. The OFF time might vary between ten minutes and 100 minutes.
Thanks for that. Yes, it appears to do the business. Bit on the expensive side, though. One will be paying for that very finely tuned increment of as low as 0.1 second, I expect. Still, I reckon there must be others out there. It also appears to be some kind of rack-mounted device, like a fuse holder or earth-leakage circuit breaker, whereas I want a 3-pin plug design to control, say, a bedside light. The closest I can get from goods on the high street is the segment timer from Wilkinson's. This has a dial 0 - 24 hours with each hour divided into four segments. You push in the little segment tab to switch on, then push another to switch off. Trouble is, the minimum time between on/off is thus 15 minutes. I'm looking for 20 seconds (roughly).
That will work as a symmetrical recycler, but the OP asked for asymmetrical 10-100min/3-90s.
Here's another asymmetrical:
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They also do a through-panel mount for it, but you need plenty of depth behind!
To the OP: You'll be very lucky to find just what you want as a "normal" item. The DIN rail units are about as common as you can get, unfortunately. You also may have to leave a little room for cooling as they all tend to run slightly warm, especially when the relay is energised.
Since my last post I fired up VB6 and wrote a program to produce a 20 second "on" time every ten minutes. It's about six lines of code and uses two timer controls. (With a bit of jiggery pokery one could probably get away with a single timer control.)
As I have already dabbled with controlling a Basic Stamp and found it to be an absolute doddle for switching on/off LEDs from the PC, one possible approach would be a PIC of some kind (to receive a RS232-type signal), plus a relay, plus a small number of supporting hardware bits and pieces (resistors etc), all of which (except the PIC) I probably already have in my rummage drawer.
A serial connection going from the PC to the Stamp can be some considerable length, so that wouldn't be a problem, especially as I have the PC switched on most of the day anyway and have two unused RS232 connections. And the program could be provided with controls to change either interval on the fly. One of the cheaper PICs retails at around a fiver, I believe. Dunno what a relay costs, if the one I'm thinking of in the rummage box is not suitable, but it won't be more than a couple of quid I expect.
If you have no problem with getting a good low voltage DC supply and aren't afraid of the programming, a PIC and relay seems like a good way to go. Basic PICs are less than that, IIRC. Maplins do the 12F675 or the
16C505 for under £2 each.
Also, do you really need PC control or could a DIP switch or pot vary the settings for you and leave the PC free?
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