This launch controller can be used with low voltage battery igniters, which fire rocket engines in model rockets such as the Estes range. These circuits are electrical, only switches and contacts are involved. The circuit for a single rocket is shown above
A point to note here is that this controller uses "C" cells, providing more current than "AA" batteries and that the push button switch has contacts rated 1 amp or higher. The wire to the igniter is isolated via a 3.5 inch jack plug and socket. Connect the igniter, then plug in to control box and then press button, making sure you are the recommended distance away. Below is an internal and external picture of my controller
Multi Launch Controller Schematic
Once again, nothing too complicated. The single pole rotary switch has contacts rated 1 amp so can easily handle the 400 mA of current that the igniter takes. Here three rockets can be launched by rotating the switch. The Green LED provides continuity between battery,igniter and wiring. This extinguishes as the launch switch is pressed. Once again, observe safety precautions.
Click for a close up picture of my rockets, file size in brackets.
Source: zen's circuit directory