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1 March 2015

How to blow up an LED

I had no intention of doing any projects today, but somehow I've been lured in. It all started with me wondering if I could add a light emitting diode (LED) to my Piezo Buffer circuit. Wouldn't it be cool if it lit up when the circuit had power? Hmmm...

You'll see here that I just happen to own a box of LED bulbs. It was only as I was taking a look at them just now that I realised that don't know anything about them. How would I get them to work if I don't know what voltage or current they need. The answer was only a Google away.

The circuit above can be used to figure out the voltage and current required to drive any LED.

The 9v power is DC to drive the circuit.

The circle component represents a lamp, or LED in this instance. When fitting these to your circuit be sure to place them the right way round - polarity matters.

The resistor component represents a potentiometer (i.e. variable resistor). I'm using a 500k pot, but I reckon you can get away with probably any.

The basic idea is that you turn the resistance up to maximum which cuts off the current that will flow around the circuit. Then you switch the power on and gently turn the pot down until the LED is lit.

At this point you can measure the voltage with a multimeter by switching the multimeter to DCV (20 volts) and touching the LED pins with the multimeter probes. My LEDs seem to all light up around the 2.7 volt mark.

You then switch the power off, break the circuit and make the multimeter bridge the gap by attaching the red probe to the positive and the black probe to the negative sides of the circuit. Switch the multimeter to DCA (200m) and switch the power on. The bulb will light up and the multimeter should tell you how much current is flowing. For my LEDs I'm seeing 1.2mA which seems far too small compared to datasheets I've been reading, but what do I know.

This was a bit of a surprise. See how the LED has exploded. It went with a pleasing crack.

Yep, I blew loads of LEDs in the making of this post. Ha ha! I can't say that the smell of burning electronics does a great deal for me. Most just flashed and died. This one split in half and sent me diving for cover! I wasn't expecting that! Ha ha.

Here's the pot I was using standing proud and in pieces, in front of the burnt out LEDs.

You won't believe this... but it started smoking when I was doing a test and I destroyed it. Oh dear! Perhaps it does matter what resistance you use?

I did manage to capture a short video of the working circuit. Contrary to the title... this was in fact the only LED I didn't blow up.

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