This week’s assignment from the League

"Write a step-by-step guide on how to do something. This could be a real world project or a fantastical one, so do with it as you will."

I'm a Electronic Engineer, so I want to do something electronic related. This guide is about...

"How To Prove your Body Generates Electricity"

Materials you will need:
- A protoboard
- A 5 volts power supply (I'm using an old computer power supply).
- 3 transistors with code 2N3904.
- 1 Diode
- the tiniest smallest littlest DC motor you can find (I took mine from a broken computer CD reader)
- Optional: colorful LEDs!

This is how this kind of transistors, LEDs and diodes look:

Ellie Sattler is holding a pair of transistors. There are bigger transistors for bigger voltages and currents. The human body generates a very little amount of electricity, so we are working with tiny components.
Alan Grant has in his right hand a rectifier diode, remember the grey line, it is important. In his left hand there is a LED, a kind of diode that emits light.

Next step, assemble this circuit in your protoboard:


First, I drew the electronic diagram of the circuit, then I awesomely poorly drew how you have to put things together: the transistors have their flat size looking at you, so their right pin goes to the positive terminal of the power supply. The side of the rectifier diode with the grey line goes to the same positive terminal too, the other side goes to the left pin of the last transistor. The motor has no polarity. For the LEDs, the shorter pin goes to the motor, the larger goes to the left pin of the last transistor.
The rectifier diode is just for protecting the last transistor for any induced current coming from the motor.

This is how I connected everything:


A close up:


I connected three LEDs just for fun, one is enough.

To make it work, just touch with your finger the base of the first transistor, the disconnected one. A least the LEDs must light on, if the motor doesn't move is because you choose a too big motor. It is the tiny amount of current on your skin that allows the current flow through the LEDs and the motor.

Now, the explanation YAY!:
Transistors has three terminals: Collector, Emitter and Base. I'm using these transistors in their switching mode. That means that as long as they get a current in their base (for the transistors in this guide is the pin at the center) they let a proportional current flow from Collector to Emitter. This current is around 150 to 180 times the current in the base. As the current we want to test is so small, we need three transistor in chain, a 150*150*150 = 3375000 times the current on my skin to move the smallest motor I have!!
This array of transistors is called a "Darlington Transistor Array".

Wanna see this thing working, JUST LOOK!!