How do I calculate the high time and low time of a 555 timer circuit? R1= 1K Ohms R2= 68k Ohms C= 2.2 pF?

Question

R1= 1K Ohms
R2= 68k Ohms
C= 2.2 pF

Answer 1

2 pF is much too low a value for this application. The timing cap should be at least 1000 pf for any accuracy. It can be as low as 200 pF.

in the one-shot mode, t = 1.1 RC where R is the resistor between pin 7 and VCC, and C is the capacitor from pin 7 to ground.

In the astable or free running mode, there are two times, high and low.
the reference has more info.

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Answer 2

Here is a site that helps you enter component values for it to calculate with (and lets you run a simulation)

http://www.doctronics.co.uk/555.htm#asta...