Led Tester / Current Limiter

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About: Disclaimer: The author is not responsible for loss of life, limb or property. The author is not responsible for your actions. The author is not responsible for anything. In fact, the author is completely i...

I use LED's in plenty of projects and art pieces. I've been caught a couple of times by a bad led so I like to test them first...

I bought a simple tester for small LED's but decided to make one myself for high powered LED's.

Now I know there are plenty of ways to test LED's. Well, here's one more.

It also good for testing small electronic devices of unknown condition.

It's essentially a current limiter with a digital panel meter.

Step 1: Making a Nice Case the CNC Way

I got fancy and used a CNC to cut out the front panel to hold the meter and the switch. A Dremel works just fine too. I'm a little dangerous free-handing with a Dremel so that's why I got the CNC...... I do this with many of my projects. You can even engrave legends and logo's this way.

I used a Compaq 16V laptop supply since I had a few lying around. The meter operational power input is rated for 5-30V so keep that in mind when picking your supply. I attached the meter power directly to the input. You could add a zener diode in series with the meter supply lead to raise the limit a bit to handle 36V input. The meter range itself is 0-100V so a separate and isolated meter supply would allow you to use the full range.

Step 2: Simplistic Design

I assembled mine in a Radio Shack project box. Most people use a potentiometer for variable current control. I took a different approach. I had these SCSI address selector switches in the junk drawer. using a bunch of 10 ohm resistors I made a simple selector. the output current will be the value of the switch times 100Ma.

Some of these switches have stop pins that block certain positions like 0 or 7 and beyond. The stop pins can usually be removed or just relocated. My switches go from 1 to 7 by default so I left them alone.

You could extend this to use BCD or HEX switches by adding another bunch of resistors.

Step 3: Testing an RGB LED

I tested a few RGB LED's. its nice to be able to check the forward voltage of each section too. sometimes I cheap out and use series resistors in my LED drivers rather than current sources. This way I can select the right resistors for each section.

I tested all sections at the 200Ma setting. The RED section was about 7V. The Green was about 9.5V and the Blue was almost 10.5V....

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    2 Discussions

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    Eric Brouwer

    2 years ago

    Very interesting version of the LED tester.

    . If I am correct, this is to test high-powered LEDs.

    1 reply
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    rjkornEric Brouwer

    Reply 2 years ago

    yes, I updated the text to show that. thamks!