Cutter activation circuit

Cutter activator

The cutter is activated by a separate logic circuit. The idea is that the circuit in this way may operate independent of the remaining electronics system. This means that even if the system encounter a software bug the parachute circuit will still activated the cutter which in turn can deploy the parachute. 

 

The circuit consist out of three main build blocks. The first block is a pressure sensor together with some additional analogue components including a operational amplifier connected as a Schmitt trigger.  The Schmitt trigger is aimed at about 12,000 meters and in order to trigger it the pressure have to increase to the level of about 5,800 meters. This means that the experiment needs to first pass the pressure  felt at 12,000 meters in order to get triggered. The main purpose of the Scmitt trigger is however to reduce eventual fluctuations from the pressure sensor.

 

The next part of the system is a D-type FlipFlop circuit  which have two outputs. Beside being connected to the Schmitt trigger it is also connected to the safety pin of the umbilical connector in order to avoid any activation of the cutter while the FFU is still in the rocket.  When the FFU have left the rocket and the Schmitt trigger is triggered at 5,800 meters the FlipFlop switches output state.

 

The last build block of the cutter circuit is the timer segment which controls the high period of the oven cutter. The time needed for a cut is about 23 seconds during -20. The circuit principle is that the cutter will remain on until the delay capacitors reach to high level for the NAND gate. To ensure a cut the period has been set to 50 s.