Re: Looking for a Low Cost On Delay Timer

[unruh <unruh@xxxxxxxxxx>]

On 2013-08-28, Guv Bob <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> "unruh" <unruh@xxxxxxxxxx> wrote in message news:lAHSt.180556$po1.28313@xxxxxxxxxxx
>> On 2013-08-26, Guv Bob <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>> > "Guv Bob" <guvbob2003@xxxxxxxxxxxxxxxxxxxxxx> wrote in message news:1_udnQ7rBpNjRo7PnZ2dnUVZ_sidnZ2d@xxxxxxxxxxxxxxxx
>> > Names can be confusing, so here's what I'm doing....
>> >>
>> >> http://img43.imageshack.us/img43/7434/wvm.gif
>> >>
>> >> When 12VDC is applied to the input, I need a 12VDC output for 5 seconds.  Then output will go back off and stay off until the input goes to zero.  Then cycle starts again.
>> >>
>> >> Current for both legs is in the 10-50ma range.
>> >>
>> >> A simple on-delay timer would work but I'm having trouble finding one with NC contacts.  Tons of stuff $100+, but for this application, it has to be under $20.
>> >>
>> >>===
>> >
>> > Thanks for all the tips and good info.  I had wanted to put something together from components but my brain is too far behind these days.  I'm going to give this a shot and hopefully I'm not picking the wrong one.  It's $5 at Frys...
>> >
>> > Velleman MK111
>> > http://www.vellemanusa.com/downloads/0/minikits/manuals/manual_mk111.pdf
>>
>> Except that looks like an oscillator rather than a "oneshot"
>> You said that you wanted something that if the input was larger than 5
>> sec, the output would go high for 5 sec, and then drop to 0. If the
>> input droped before 5 sec was up, you wanted the output to drop as well.
>> Then you wanted it to wait until the input went high again before doing
>> that again.
>> This device has a relay (why would you need a relay for 50ma? Most ICs
>> can handle an ouput current of 50mA at 12V without the need of a relay.
>>
>> This kit is an oscillator, where you can adjust the time it is on and the
>> time it is off with the pots. It has no input.
>>
>> It uses a 555 timer chip. The primary design of the 555 is to initiate a
>> pulse when the input goes high, and stays high for the requsite time
>> even if the input drops again. If the input stays high beyond the time
>> Ie, I think you want to think your way through what you need carefully.
>
> Thanks, yes you're right.   What value resistor could I substitute for RV1 to give a pause time between pulse to 10 minutes?

RC=t roughly. (depends on exactlywhee in the charge/discharge cycle the
thing triggers). But R probably should not be much over 1Mohm, as
otherwise the input resistance of the ic becomes important.
Then C should be about 600uF (probably not electrolytic as the internal
resistance can become important but finding anything else at that size
is pretty impossible)

)



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