28 Jun

At the end of the last semester of Monaghan Coder Dojo, I promised the students we’d do something cool for the next series of classes. We’re going to build a Gauss gun.

A Gauss gun is a rail, which a metal projectile travels along. It has a series of electro-magnets on it. As the projectile approaches each magnet, the magnet turns on, accelerating the projectile in towards the center of the magnet.

As the projectile reaches the center, the magnet turns off, so the projectile travels through it, and on towards the next magnet.

The same trick is done a few times, accelerating the projectile more and more each time, until it finally reaches the end of the track.

The first thing I had to do was design a circuit which you can turn on electronically that will stay on, and which you can then turn off electronically. I mean, the circuit should not involve a switch that requires physical effort to turn on and off, as that may slow down the projectile.

So, the solution I came up with was:
1. a circuit which uses a transistor to turn on. This way it can be enabled by shoving a little bit of power through the transistor’s base.
2. the circuit, once completed, will feed a little bit of its output electricity back into the transistor’s base by using a capacitor to give a smooth and continuous power line.
3. to turn it off, we will short-circuit the capacitor.

I did a quick “proof of concept” with an LED.

In the next article, I’ll show how to adapt this so that the “switches” are photoelectric cells, so you can turn the circuit on by disrupting one light beam, and turn it off by disrupting the next.