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?
R1= 1K Ohms
R2= 68k Ohms
C= 2.2 pF
Right, I know the equations but I cant figure out how to calculate Ohms vs Pico Farads... Forgot to add that in.
- billrussell42Lv 71 decade agoFavorite Answer
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.