Author Options:

Using Capacitors in a flip flop LED flasher circut? Answered

Hello guys,

I am very new to electronics, so please bear with me. I am trying to build using specs from various places a seemingly simple flip-flop led flasher using a 9V dc power source, a pair of NPN transistors, a pair of capacitors, a resistors. Now I have built the circut several times on my breadboard. I have yet to get the circut to work.

I tried to troubleshoot the problem myself, and done a little research. It seems that capacitors wont work with a dc current, or so most of the web sites say. The problem is all of the circuts I have seen use capacitors, even the 555 circuits. The only thing I have done different from the diagrams is I am using a slightly larger (30 or so farads) cap. They are the the ceramic disc type. Am I using the wrong caps? Not sure what I am doing wrong?


Thank you gentlemen, I was indeed reading the mfg sheet wrong. It was showing from the bottom, I was reading as in the top. Jeez....what an idiot I am. Thanks again.

Are you using 100uF electrolytic capacitors?


30 FARADS! That is a very large capacitor, more like a battery than a cap, at least for use in a timing circuit.

Do you mean 30 microfarads perhaps? or 30 nanofarads?

555 timers are probably going to fail miserably if 30 Farads is used as the timing cap.

For the record, when a long time duration is required on a 555 timer circuit, it's usually much easier to boost the value of resistors than it is to boost the value of the capacitor. 30uF isn't too bad, but much over that means you're not looking at the RC equation right, at least ime.

Please post your schematic, required flash rate, and ideally, the forward voltage and forward current of the LED being toggled, so that potential responders (including, but not limited to myself) can evaluate the efficacy of the initial design to start and potentially offer alternative designs that will meet your design goals. We can go from there.

Here is the schematic. And yes, I meant microfarad. Sorry about that. I have assembled it a few times, and it will not work. It should. Does it matter if I am using the ceramic disk caps?

Correct me if I'm wrong, but those are electrolytic capacitors, not ceramic disc capacitors (they are polarized). You need the ones that look like little cylinders.

Gotta agree. They do look like they're supposed to be polarized caps, rather than bipolar. You sure you're 2N2222s are correctly oriented? Make sure to check the data sheet carefully. They sometimes show the pin-out as viewed from the bottom, sometimes from the top and it can be easy to flip the collector and emitter..

I've done the CBE or EBC backwards many a time.

It's not so bad except on occasion when it results in the genie getting out.

Kinda irritating how in certain cases, mfgs show the pinout from component side and in others from solder side. I've seen a few datasheets over the years where they didn't even bother to note which view they were using.

FTR, edit and post the schematic to your question.

That should work. What happens ?


Well, one or the other should light.

Cheat. Tie a 1K resistor from the supply to the base of Q1 or Q2. What happens ?

If you don't turn on the lamp, you LEDs are the wrong way round, or your transistor is broken, or wired wrongly.