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555 timer

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New Member
:D hello to everybody and to the experts in using the 555 timer ic

i have wired up a 555 to activate and deactivate a device. instead of directly installing the RC network to get the desired time, i expermented by using a 30 second interval. i have put a 1k connected to pin 3 to pull up the voltage of the output to supply voltage. the unit functioned except the time difference of the on/off period. below is the result of my exp.

time measurement at initial turn on t measure after 5 minutes
on - off 45s on - off 27s
off - on 20s off - on 24s
on - off 35s on - off 24s
off - on 15s off - on 15s
on - off 35s on - off 28s
off - on 15s off - on 18s
Average on time 38s Average on time 26s
Ave. off time 16s Ave. off time 19s

t measrue after 10 mins.
on - off 24s
off - on 19s
on - off 26s
off - on 19s
on - off 25s
off - on 19s
Ave on time 25s - Ave. off time 19s

as can be gleaned from the 5 min. time and the 10 min. time there is a time difference of about 6 seconds.

my question is, is there a way to narrow the time gap of the on/ off time?

any suggestion would be highly appreciated. :D :D :D


New Member
the duty cycle must be kept at around 50%

programs which simulate 555 circuits can help to determine the correct resistor values



New Member
:shock: You should check the values of the capacitors... this are very likely to be temp. sensitive, especially if they are cheap.
Do check the Vcc, if this changes your timing will drift...


New Member
555 on/off difference

:D hello again,

1. the Vcc does not vary and the caps am using are good kinds inspite the proliferation of cheap caps here.

2. to Kane: now why did i not think of that before, the Duty Factor where the time duration of the output pulse is near V+ level and the time duration of the output pulse is near ground voltage level.

i believe this would solve my problem.

thanks guys :) :) :) :)
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