Our launch controller is built inside of a recycled ammo box, with the batteries and wires inside, a hole for the safety key, a status LED, and the not very big red button on an outside face, and wires to connect it to the rocket coming out of the side.

The controller was built in one meeting, and used the next week to test launch a small firework. The following week we used it to launch several rockets build by the junior members.

A circuit diagram of the entire contraption is shown below:

We chose the resistor value so that there was minimal voltage drop (and and thus current) over the actual ignition element unless the red button is pressed. We approximated it's required resistance by taking the LED's amperage requirement, as well as the voltage of the battery, and plugging them both into the formula V/I = R

Throughout the process of building this, we experienced several problems.

Cord construction (what Walter & Jimmy did): To make the cords we had to cut the wire into two equal-sized pieces, strip the ends of both, and wind one end of each through a metal clip. The first parts were easy enough, but the last step took about an hour.

Drilling holes

Constructing and mounting the safety; realizing it could be improved by changing the angle

Mounting the LED

Mounting the button

Soldering the connections

Twist cramping, concerns about conductivity