On Delay Timer with Capacitor

Thread Starter

Delta_374

Joined Oct 18, 2016
5
Hi
I have been a bit unsure how exactly to create a time delay on a circuit I've been working on. I want to use a 100 uf capacitor with a variable resistor to control the charge rate, and I would like it to close the circuit once it's done charging and continue to output charge until power is cut from the capacitor. Can I just have a variable resistor in series with a capacitor?

Thank you
 

MrChips

Joined Oct 2, 2009
23,094
Hi
I have been a bit unsure how exactly to create a time delay on a circuit I've been working on. I want to use a 100 uf capacitor with a variable resistor to control the charge rate, and I would like it to close the circuit once it's done charging and continue to output charge until power is cut from the capacitor. Can I just have a variable resistor in series with a capacitor?

Thank you
Sure you can. Who is going to stop you?
 

AnalogKid

Joined Aug 1, 2013
9,078
Yes, but the R-C node cannot supply much power to an external device or circuit. Better to have the R-C exponential ramp drive a comparator. In this way you get a clean, rapid transition at whatever delay time you select the components for.

When you say "close the circuit" - what circuit? Can you share the details? without them, it is not possible to narrow down the dozens of ways to do what you want.

ak
 

Thread Starter

Delta_374

Joined Oct 18, 2016
5
Thanks for the replies! Pretty much, in the simplist form, I am going to have a phototransistor trigger off a regular NPN transistor when light is detected. I want the NPN transistor to complete the circuit to power up a optocoupler, but after a delay. The delay is the only function I am trying to add in.
 

MrChips

Joined Oct 2, 2009
23,094
Thanks for the replies! Pretty much, in the simplist form, I am going to have a phototransistor trigger off a regular NPN transistor when light is detected. I want the NPN transistor to complete the circuit to power up a optocoupler, but after a delay. The delay is the only function I am trying to add in.
A picture is worth a thousand words.
A circuit diagram is the language of electronics.

Draw us a circuit diagram then we can start communicating.
 
Top