Hi,
I'm getting some help on another forum but getting some conflicting advice.
I need the attached circuit and have lined up an 18v 7555 and most of the bits for it. The circuit will constantly be supplied by car +12 (relatively unsmoothed DC from 12 to 14.4v, 16v max to be on safe side) and the trigger side will be supplied from the same source. I want the circuit to produce it's output once only, when I cut the trigger supply (circuit will remain powered throughout).
But... someone else suggested I shouldn't use the values suggested in the attached and instead use a 10 meg pot + 1 meg fixed and a much smaller cap of 5uf.
I don't know enough to work out if/why this is 'better' or more 'stable'
I'm not worried about the out of the box time, that's what the trimmer is for. So long as it can go from 1 to 60 sec give or take 5 sec and once trimmed to the correct time can be left for a couple of years and not require a trimmer adjustment that's all I need. If it counts, the longest the circuit would be powered is a few hours, before being shutdown overnight (used in a car).
Comments appreciated as I really need to fix on the componants and get them ordered, I'm buying good quality stuff too so best if I can just spend on what I need, though the resistors and caps are not expensive.
Thanks, Greg.
I'm getting some help on another forum but getting some conflicting advice.
I need the attached circuit and have lined up an 18v 7555 and most of the bits for it. The circuit will constantly be supplied by car +12 (relatively unsmoothed DC from 12 to 14.4v, 16v max to be on safe side) and the trigger side will be supplied from the same source. I want the circuit to produce it's output once only, when I cut the trigger supply (circuit will remain powered throughout).
But... someone else suggested I shouldn't use the values suggested in the attached and instead use a 10 meg pot + 1 meg fixed and a much smaller cap of 5uf.
I don't know enough to work out if/why this is 'better' or more 'stable'
I'm not worried about the out of the box time, that's what the trimmer is for. So long as it can go from 1 to 60 sec give or take 5 sec and once trimmed to the correct time can be left for a couple of years and not require a trimmer adjustment that's all I need. If it counts, the longest the circuit would be powered is a few hours, before being shutdown overnight (used in a car).
Comments appreciated as I really need to fix on the componants and get them ordered, I'm buying good quality stuff too so best if I can just spend on what I need, though the resistors and caps are not expensive.
Thanks, Greg.
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