Beginners guide to LEDs


One of the most satisfying things you can do when building your radio controlled tractors or construction vehicles is to add LED lights. You can very quick see the fruits of your labor even before you’ve sorted out the control you can just temporarily wire them up and get a sense of what the finished tractor will be like.

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LEDs or Light Emitting Diodes are a simple low power light source which are used in pretty much every electronic device on the market these days, I guarantee that the device you are reading this on has at least one LED.

LEDs are made from semiconductor material. In simple terms when current flows through the diode electrons are able to move from the negatively doped region of semiconductor material to the positively doped region and combine with the holes in the p-region. This recombination releases energy in the form of photons which, if in the visible spectrum, we interpret as coloured light.

When you are working on your vehicle you need to know a few things about your LEDs.

  1. How many you want to control from one signal
  2. What is the limitation of your signal source
  3. What is the voltage of your signal source
  4. What is the diode forward voltage
  5. What is the diode forward current

Lets take the example of a possible RC tractors headlights, 2 super bright white LEDs with a forward voltage of 2 volts and a forward current of 20mA. I want to send a signal from my Atmega 328P running at 3.3 volts to switch them on.

First we need to know if we should put the LEDs in series or parallel. We have 2 LEDs with a forward voltage of 2 volts each, therefore in series we would need a 4 volts to run them in series. Our signal is 3.3 volts so we must wire them in parallel.

Lets say we want to limit the current to 20mA from our chip so that we don’t damage it. That means we want 10mA on each LED, so we use the following equation


This gives us a value of 130 Ohms but the nearest common resistor value is 150 Ohms so we’d go with that.

I’m sure I’ve probably forgot something here so if you notice a mistake or have some suggestions then let me know on the RC Tractors Forum. Check out the RC Tractors component page for other components you might be interested to learn about.

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