Can't get capacitors to work...

[earlz]

Ok, I am beginning some experimenting with electronics..

I can't seem to get capacitors to work though, all I ever get from them is a very short blink(connected to a LED)while it is charging, and then the LED is off and stays off until I discharge the capacitor

I am using a 47uf electrolytic capacitor and it is rated for 50V,

Basically, this is how I have this simple thing connected..
Vcc(positive 5V) connected to + capacitor lead. - capacitor lead connected to 220 ohm resistor. resistor connected to positive LED lead. negative LED lead connected to GND...

What exactly am I doing wrong? I thought that using this circuit that either the LED would stay lit or that it would blink on and off; but it just blinks and stays off while the capacitor is charged... I'm not understanding this...

[whowhatwhere]

Digital flip flop.

Flapjacks and a Weiner.

WHEEEEE.

[JohnnyTheDon]

That is the way a RC circuit works. The capacitor charges until it reaches the voltage of the source, and then stays there. A fully charged capacitor acts like a break in the circuit. IIRC to make it blink you need a transistor, and there should be plenty of examples on the internet.

[earlz]

That is the way a RC circuit works. The capacitor charges until it reaches the voltage of the source, and then stays there. A fully charged capacitor acts like a break in the circuit. IIRC to make it blink you need a transistor, and there should be plenty of examples on the internet.

well I tried constructing like 3 examples and none of them actually worked

[xDDunce]

capacitors discharge in the opposite direction to their charge direction. hence why an LED and a capacitor in series has a constant current, and they discharge the battery when in parallel.

to get a single blinking LED try using an NE555 timer. or alternating blinking LEDs are more simple.

both circuits here (alternating LEDs at the top, single LED about 3/4 the way down - remove LED1 to make it a single LED)

Cheers,
James.

[Velko]

First circuit in xDDunce's link is a classic one I remember soldering that when I started with electronics.

Also you can try first one here. I "upgraded" my TV's remote with it (slightly different capacitor and resistor values, trough), so I could find in in the dark .

[earlz]

First circuit in xDDunce's link is a classic one I remember soldering that when I started with electronics.

Also you can try first one here. I "upgraded" my TV's remote with it (slightly different capacitor and resistor values, trough), so I could find in in the dark .

I don't have any PNP transistors, is there a way to work around that with NPN ones?

[earlz]

oh wait.. now I got it to work.. had to fry 3 transistors before I realized I left out the 470 ohm resistor(so 9V was going through them) or well, out of the circuit, like it was on the board but one lead wasn't connected to anything lol..

yea.. transistors get pretty hot though with 9V running through them.. I burnt my finger a little feeling it..

[Owen]

Whoa whoa whoa! Nothing in that circuit should be passing enough current to heat up a transistor!

[bewing]

You will if you just short 9V straight through it in one of the wrong directions.

[JohnnyTheDon]

IIRC you don't want large potential differences across the base-emitter. I'm not really sure though, stupid electrons going one way and "current" going the other always messes me up.

[earlz]

btw, I decided to hack a USB cable so that now I can get a good stable +5V without having to rely on batteries and such... plus if I get far enough, I can even mess around with the data + and - wires.. though I doubt I'll do anything with it anytime soon

[JohnnyTheDon]

btw, I decided to hack a USB cable so that now I can get a good stable +5V without having to rely on batteries and such... plus if I get far enough, I can even mess around with the data + and - wires.. though I doubt I'll do anything with it anytime soon

I hope you don't care too much about the computer thats wired to that, if you wire something incorrectly you could fry your USB controller.

[earlz]

btw, I decided to hack a USB cable so that now I can get a good stable +5V without having to rely on batteries and such... plus if I get far enough, I can even mess around with the data + and - wires.. though I doubt I'll do anything with it anytime soon

I hope you don't care too much about the computer thats wired to that, if you wire something incorrectly you could fry your USB controller.

yea, I'm aware.. and it's an old computer with already half broken USB ports anyway lol