LED Project for the clueless

Thread Starter


Joined Aug 2, 2013
I'm pretty clueless. This is just a personal project and I desperately need some help.

I am trying to build an LED flash unit. Just like a camera flash unit but less powerful, a lot simpler and lower voltage.

My idea is this: A 3v coin cell charges a capacitor. A button pressed allows the current to flow from the capacitor to the LED and the LED glows only while the capacitor is discharging.

If the switch remains closed, the LED goes remains off after the capacitor has discharged. If the switch is opened, the LED goes off after the capacitor has discharged and the capacitor begins to recharge.

Can anybody help?


Joined Sep 9, 2010
That's a little tougher than you might think. An LED can be damaged by too much current, which is exactly what would happen if it was connected to a big enough capacitor. A smaller capacitor might be chosen to deliver a flash without enough energy to destroy the LED, but it could be challenging to zero in on the right value.

One alternative would be to also use a current limiting resistor, but this might not produce a "flash" so much as turning on and fading off. Again, a little testing might find a combination that works for you, where the fade is not too slow.

There are many other ways that might give a better result but they are a bit more complicated. A 555 timer IC circuit called a "one shot" would be ideal I think. It could turn on the LED to maximum brightness for a duration of your choosing.

You may have to also deal with low voltage. Could you live with 2 cells in series to give 6V?