Hello,
I have a question about the uF's of capacitors. If we were to charge a 1.0uF capacitor, about how long would it be able to keep a simple LED lit when we remove what was charging it?
Sorry for double posting, but wanted to also ask if there was a way to check the level at which the capacitor is filled, to show when it is full.
you should read about capacitor time constants. but you'd probably learn more if you just grab some different sized capacitors, an LED, battery, and have fun!
(if that doesn't help, the answer is: not very long! (see below))
Here we go...
It takes roughly five time constants (5[ch964]) for a capacitor to charge and discharge.
With a 1µF capacitor discharging through an LED with a current limiting 100[ch937] resistance (for arguments sake):
[ch964] = RC
= 100 x 0.000 001
= 0.000 1 (seconds) or 100µs
5[ch964] = 500µs
So the LED should stay on for around five hundred microseconds, but this is of course not taking into account leakage current, stray capacitance, LED voltage drop etc.etc.
Anyone else want to take into account those additional factors for me?
/me
It will be much shorter than this. the LED will only be lit as long as the output voltage is above the forward volt drop of the LED. So that is normally 1.3v. Without calculating it then that would be about a time constant.
I wouldn't use a 100R resistor as that is too small. push it up to about 800R and it will say on longer.
However it is best to start at the other end of the problem. how long do you want it to stay on. then work out the capacitor for this. It will much bigger than 1.0uF for any length of time.