A 555 will switch, by design, when the voltage of the timing capacitor is at 1/3 or 2/3 that of the Vcc.I have a 555 which is designed to hold the signal high for 15 seconds. When I supply power it goes high for 25 seconds and the goes low. After it goes high it holds it high for the 15 seconds. Why does it hold for 25 seconds in the beginning?
I got this to work, thanks. What is the best way to discharge the capacitor after the 555 goes high?Connect pin 4 (reset) to Vcc through a 100K resistor (approx) and also to ground through a 100uF capacitor. When the circuit powers up, the capacitor will hold pin 4 low (thus the output will be low) until the capacitor charges up sufficiently to make pin 4 high and the astable starts up.
You will have to play around with the values to get it to exactly 15 secs but the principle holds.
You need to start posting schematics on how your circuit is currently configured.I got this to work, thanks. What is the best way to discharge the capacitor after the 555 goes high?
thanks
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