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- 555 timer setting
February 1, 2006, 4:34 am
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I am using the 555 timer for a basic circuit. I am using the circuit in the
back of the Dick Smith catalogue Can anyone help me with the values of the
Cap and resister. The time I want is 2 minute (120sec) +- 10 seconds. I
have tried various values, but it is unreliable, and on most occasions stays
on for a long time, and I can't wait that long and normally manually reset
it. If someone can give me the right values, then I may be able to see if
the time problem is somewhere else in the circuit.
Thanks in advance for any replies.
Re: 555 timer setting
** Lemme guess - you have 2.2 Mohm resistor and a 100 uF electro cap ??
The cap has as much resistance (leakage) as the resistor so never charges up
Get say three *tantalum" caps 10 uF, 25 volt, & use them in parallel with a
3.3 Mohm feed resistor.
This will give about 70 - 80 seconds delay.
Then put a 10 kohm trim pot from pin 5 to the + supply and adjust to get the
exact time you want by adjusting the comparator trip voltage.