2 May 2013

Another simple electronics project for kids

Project Features

  • Simple
  • Cheap
  • Doesn't take long
  • Can be done by children (with a little help)

One of my sons recently started to nag me. He wanted to solder something. Initially I had no idea what he could solder and I thought he was simply bored. But he kept going and I knew I had to find something. Finally I remembered that it would be "Blue Night" soon and that I wanted to take my kids there. So we could build some coloured light object to be worn at the event.
I looked through my unused hoard of components and found the bag with one hundred rainbow LEDs (i.e. slow colour changing LEDs). I had ordered them from China for little money - for no good reason really... 
And so was born the idea to build a little pendant of 3x3 LEDs.

Obviously, for this project, we need 3x3 colour changing (a.k.a. rainbow) LEDs. They usually look like normal LEDs, have two pins and a water-clear body.

Next, you will need a piece of strip board...
 ..and of course you need solder, some wires and some kind of battery holder.

Building it
It really isn't complicated. Keep in mind that LEDs have two different pins: Anode (+) and cathode (-). The cathode is marked by a shorter wire.
Since all LEDs will be connected in parallel, they should all have the same orientation.

Our design was going to be a 3x3 configuration, so we started with a row of three LEDs. Insert the LEDs in the strip board so that all three cathodes and all three anodes end up on the same respective copper strip. Bend the wires so that the LEDs can't fall out and solder. Like so:
Not perfect, of course. But when I was six years old, I couldn't solder at all...

Next, cut of the wires (not easy with small hands).

First row finished!

Add a second row (mind the LED's orientation!):

And solder again.

And finally a third row gets soldered.

Now we need to connect all corresponding copper strips. See in the photo above, how this was done with some wire cut-offs. Note, that we were able to fit two wires in the middle hole.


And do the same thing with the other three copper strips.

Finally, solder a power supply cable to that piece of art and hard work. By convention, the wire to the anodes should be red and the wire connected to the cathodes should be black.


Above you see an additional wire loop so you can attach a neck strap. And there you go. One satisfied customer!

As power supply we used a set of 4 rechargeable AA cells with a total of approximately 5 volts. There are no current limiting resistors. With the LEDs used here, the current into the LEDs was measured at somewhere between 18 and 35 mA with those 4 AAs. This is more or less within specs. Total current consumption is under 300 mA, so the AAs will last for a few hours. Long enough for a visit to the "Blue Night"!

A nice effect results from the fact that the LEDs fade with different speeds. Initially, all LEDs show the same colour. But gradually the colours drift apart and then you get a random colour pattern.


The LEDs are VERY bright. In fact, they are so bright that my camera can't take decent photos. With standard settings the colours all look like white. With shutters closed as far as possible and exposure at minimum, colour is visible. But then you don't get an impression of the brightness...

Hm, perhaps I should steal this and do some light-painting...


  1. Cool electronic project, does it also change or blinks.

    1. Yes, it does. We used colour changing (a.k.a. rainbow) LEDs.