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Rudolph the LED flashing reindeer

Being a dad, I know that children are curious and that they are eager to learn new things. So, when dad has been bitten by the electronic bug – it is obvious to engage in simple electronic projects for kids. If you want to make something creative with your children or teenagers, it is easy to find interesting electric circuits to build together.

I have made this project together with my 7-year-old daughter – we wanted to make a Christmas ornament and build a simplistic electronic circuit board with PCB layout board design.
We decided to make a classic Christmas Reindeer decoration – we have chosen the name Rudolph the LED flashing Reindeer.

Rudolph is made with a combination of children beads based and 3x flashing LEDs. I wanted to create something rather simple, it would of course be easiest to flash the LED using a standard Arduino. But I thought that an Arduino would be overkill, and I also wanted to make something with a longer battery lifetime.

We have created the flashing LEDs using a classic astabile multivibrator – combining two NPN transistors and two capacitors.

This project is not about teaching the children about formulas and equations – much more about getting the children involved by these circuits to discover current and the electronic world themselves. It is about to see the effect and then to understand the background later.

Components needed:

  • 2x, 330 Ohm resistors
  • 2x, 33 kOhm resistors
  • 2x, NPN transistors
  • 2x, Yellow 5mm LEDs
  • 1x, Red 10mm LED
  • 4x, 1.5V batteries
  • 1x, Battery case
  • 1x, Breadboard
  • 1x, PCB solder board
  • x, Dupont wires
  • x, Beads in different colors

Blinking led circuit

Step 1 – Breadboard

Start by building the circuit on a breadboard, this will make it easier to migrate to the backside of the reindeer later.

Breadboards or plug-in boards allow the construction of circuits without soldering. A suitable solution for test and play purposes. Breadboards are available in all possible sizes.

The prices start at €2 for a board in the size shown. If you need more connections, you can also clip the boards. The larger Breadboards also have a stable base plate and 4mm clamp for the power supply.

LED blink circuit on breadboard
LED blink circuit on breadboard

An important consideration is to remember the voltage required for LED to light properly – I have used 4x 1.5V batteries and total voltage of 6V. But you also use 12V or 9V if you remember to calculate the new resistor value, the higher input voltage the higher resistor value. You can calculate the LED resistor value here.

My daughter placed all the components on the breadboard – she has previous experience from electronic circuit board kits for kids. You should of course observe the process and verify that the components are oriented the right way – but my experience is that they quickly get a grasp of the short and long leg.

The dual LED blink circuit is fast built, it is actually a very simple circuit but inside the circuit a lot happens :-). Put simply, one could say that the capacitors charge up and the transistors block each other, so only one transistor can switch through at a time, and thus the LED lights up.

With this circuit, it depends on which capacitors and which resistors you use. Replace the capacitors and resistors with other values, you will notice that the flashing mode changes. Even if only individual components are exchanged, the behaviour changes from one LED to another.

Step 2 – Beads on pegboard

Now comes the fun part where the reindeer is created using a pegboard and coloured beads of your choice. This step


can involve the child’s smaller siblings and make the flashing reindeer a true family project.

Let the children be creative and design their own reindeer – they will be proud with the finished product.
Remember to iron the beads on both sides – this will make the design much stronger and solid.

Step 3 – Soldering and mounting the electronics

In this step you move the components one-by-one to the PCB soldering board.

The children must be older than 12 years before they can solder themselves – a soldering iron is potential dangerous apparatus and care should be taken no matter ageqq.

Small children can still take part in the soldering process – they can hold the solder wire and guide it towards the soldering joints.

When you have finished soldering all the parts and you have confirmed that LEDs still flash, then you are ready to apply hot glue on the backside. The hot glue will ensure that the electronic kit can be handled by the children without being destroyed.


The flashes are based on a circuit called a astabile multivibrator. Astabile is the opposite of stable – and the circuit is just not stable. It constantly changes state – and is astabile.

If we see the blinking output signal by “out” that is the transistor T2’s collector, the voltage will continually switch between high and low, where low is close to zero volt and high is close to the supply voltage. Therefore, the astabile multivibrator can also be used as a pulse generator in circuits, where you need a signal that switches between high and low.

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