Capacitor Circuit

LesJones

Joined Jan 8, 2017
4,174
When the last connection was made connecting up the circuit the LED would flash on and then go off. The length of the flash would depend on the value of the capacitor and resistor. This assumes that the capacitor was initially in a discharged state. With a perfect capacitor pressing the normally closed push button would have no effect. With a real capacitor which had some leakage then after holding the switch pressed for some time the LED would flash on when it was released. The time the push button needed to be held pressed for the LED to flash when it was released would depend on the type of capacitor. The time that the button needed to be held pressed would be from several minutes to many months.

Les.
 

Thread Starter

stalexa

Joined Nov 23, 2019
7
When the last connection was made connecting up the circuit the LED would flash on and then go off. The length of the flash would depend on the value of the capacitor and resistor. This assumes that the capacitor was initially in a discharged state. With a perfect capacitor pressing the normally closed push button would have no effect. With a real capacitor which had some leakage then after holding the switch pressed for some time the LED would flash on when it was released. The time the push button needed to be held pressed for the LED to flash when it was released would depend on the type of capacitor. The time that the button needed to be held pressed would be from several minutes to many months.

Les.
Thank you Les, I'm trying to design a very simple circuit to sound a buzzer and light an LED if my freezer door is left open by accident. Hence the values of capacitor and setting of the potentiometer.

So approximately after 100 seconds the LED would flash on and then go off. Is there a modification that would make it stay on till the switch was opened again? Maybe need a relay and a separate circuit for the LED / buzzer output?

S
 

AlbertHall

Joined Jun 4, 2014
12,345
So approximately after 100 seconds the LED would flash on and then go off. Is there a modification that would make it stay on till the switch was opened again? Maybe need a relay and a separate circuit for the LED / buzzer output?
The LED would come on immediately the switch is closed and then slowly fade out.
If you want the LED to stay on until the switch is opened remove the capacitor from the circuit.
 

Thread Starter

stalexa

Joined Nov 23, 2019
7
The LED would come on immediately the switch is closed and then slowly fade out.
If you want the LED to stay on until the switch is opened remove the capacitor from the circuit.
Thanks for your response Albert.
I'd like a time delay tho so the LED comes on about 100 seconds after the switch is closed and stays on.
 
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