When ematch connected:
PYRO_SNS is at 0.28V --> indicates ematch continuity
3mA going through ematch (assuming 1ohm from MJG Firewire Initiator specs) --> not enough to blow
After pulling PYRO_CTRL high:
PYRO_SNS pulled up to 3.3V
2.28A going through ematch --> blows
After event:
PYRO_SNS pulled to 3.3V --> indicates no ematch
Can use digital GPIO on VoCore2 for continuity:
VIL = 0.8V, VIH = 2V
Low = ematch connected
High = ematch not connected
LTSPICE Simulations: