I would like to use 555 with a relay to make a reliable control circuit.
I use 555 as mono-stable and the following equation does not work:
t = 1.1*R*C seconds
R = 51 K ohm
C= 220 uF
The output should be high (1) for about 12 sec but it does not. It is high for 6 or 7 sec only!! then it goes to low (0).
What causes this error? Is the previous equation ideal and I should use practical one?
I noticed that the 7 sec are constant. They don't change. Will they be constant for ever? If yes, I will increase the resistance to get 12 sec then I will continue building my project.
If 555 is not reliable, Would you suggest me any other IC to control time?