Why won't my circuit work?

Question

I have been trying to get an LED to blink using a 47 uf 50v capacitor, 33 ohm resistor and an LED. My power supply is a battery charger rated at 12 volts and 1000 mA. The LED I took out of an old circuit so I don't know the specs on it. The problem is that I have not even gotten the the LED to light up much less blink. I have hooked the whole thing up in series and I tried putting the capacitor in parallel with the resistor and LED (resistor and LED in series) and have changed the polarity in the circuit and ensured everything is put in right without success. What am I doing wrong? I bought a new LED but I don't want to use it unless I know the circuit will work. It's rated at 1.7v and 20 mA. Thank you very much for your time and have a great day.

Update:

The capacitor is before the resister and the LED is after the resister in the circuit. I figure this could be some important info that I forgot to include.

billrussell42 · Accepted Answer

You are not going to make it blink with those components. You need something active like a transistor, at least. A 555 timer chip will work best.

Leave out the capacitor till you at least get the LED to light. 12 volts is too high a voltage, or the 33 ohm resistor is too low. The combination will produce a current of about 0.3 amps, enough to burn out most LEDs.

Get a higher value resistor, somewhere between 600 and 1000 ohms, and the LED will light up OK. But you will never get it to blink with just a cap.

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turtle_titan · Answer

The capacitor in series is not going to allow current to flow.  That is why your LED won't light up.  Also keep in mind your LED has polarity, it can only be hooked up one way.   Something like this is probably your simplest bet.

http://wild-bohemian.com/electronics/flasher.html

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Why won't my circuit work?

2 Answers