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 The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

#11
09-03-2010, 11:58 PM
 abuhafss Junior Member Join Date: Aug 2010 Location: Pakistan Posts: 47

Quote:
 Originally Posted by Bernard I would also add 1k resistors between pot and pins 7 to prevent accidental connecting Vcc to pins 7 via pot setting. Looks like all 555s should come up reset on power-up.
I am sorry but, what is POT?

By the way, one friend has advised me that "15 second period generated with a 555 is not likely to be very stable" so I should go for ICM7242 or for some PIC. What do you say?
#12
09-04-2010, 05:42 PM
 Bernard Senior Member Join Date: Aug 2008 Location: Tucson AZ USA Posts: 2,916
POT

POT= potentiometer = variable resistor, or your 1M with arrow pointing at it. My one finger typing tends to make mistakes on long words, so ' tend to avoid them where possible. What are your timing accuracy requirements? Persional openion: 15 sec with 555 good for 1% or better. If far greater accuracy is needed, use a master clock, line frequency [ 50 or 60 Hz divided down to 5 sec] or crystal controlled clock driving a counter like 4017 & using gating to derive time periods. Or use 555 divided down, where a smaller cap with low temperature coeficient can be used.
#13
09-04-2010, 05:51 PM
 abuhafss Junior Member Join Date: Aug 2010 Location: Pakistan Posts: 47

Quote:
 Originally Posted by Bernard POT= potentiometer = variable resistor, or your 1M with arrow pointing at it. My one finger typing tends to make mistakes on long words, so ' tend to avoid them where possible. What are your timing accuracy requirements? Persional openion: 15 sec with 555 good for 1% or better. If far greater accuracy is needed, use a master clock, line frequency [ 50 or 60 Hz divided down to 5 sec] or crystal controlled clock driving a counter like 4017 & using gating to derive time periods. Or use 555 divided down, where a smaller cap with low temperature coeficient can be used.
Thanks for the details. I got it.
The time accuracy is not so important here, 1-5% tolerance will be no problem.

 Tags auto, timer, triggering

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