The timer controls the redundant apogee igniter. Although earlier models used I2C accelerometers to detect launch, the latest design incorporates a simple g-switch for maximum simplicity and reliability. The signals of the g-switch pass through a digital filter to eliminate bumps being mistaken for a launch event.

The timer can be adjusted in the field with a small rotation switch allowing for 16 different settings.

An Atmel 328p controls the igniter mosfet. As the low impedance of the igniter may cause a dramatic drop in battery voltage, a large electrolytic capacitor maintains adequate power to the 328p.

A beeper is installed to provide the user with audible information on continuity of the igniter and timer status.

Although electrolytic capacitors are ideal for brown-out protection during igniter firing, the wet dielectric medium of the capacitor may leak out at high altitude. As an alternative, dry capacitors may be employed, but these are bulkier and have lower capacity. To avoid the potential leakage of  dielectric medium, the 1000uF capacitor was sealed in an anodized aluminium container.


Fig. 1. Timer with sealed capacitor.



Fig. 2. 3D design of the timer board v1.0 (Designspark).


Fig. 3. Final product v1.2