/diy/ - Do It Yourself

>>1216853
>>1216857
Here. The voltage at which the FET turns on varies from FET to FET, and a probably over temperature and other things, but it should be within 10min either way. The time it takes for the capacitor to charge is proportional to R*C (its time constant), and I'd advise picking up a cheap supercapacitor for this little circuit because its pretty hard to find potentiometers with such high values. If the FET being an unknown isn't to your fancy then I'd definitely recommend using a comparator to trigger once it hits the correct voltage threshold, and then you can adjust what voltage simply by staking either terminal of the potentiometer to the high and low rails and feeding the variable tap to the comparator's input next to the RC output.