Abstract: A switch selectively connects an airbag inflator or a load resistor to a crash sensing module to enable or disable an airbag. A transistor circuit across the load resistor detects whether deployment current is flowing in that resistor. Another transistor activated by the first transistor passes current to a fuse to open the fuse, permanently indicating a deployment event when the airbag was disabled. A latch circuit holds the second transistor on to assure sufficient time to open the fuse by melting.

Abstract: A SIR system has frontal air bags and side air bags both controlled by the same microprocessor. To guard against spurious deployment of side air bags with minimal software burden, a lateral accelerometer and an arming circuit detect side crash activity and apply an arming signal to a pulse accumulator circuit in the microprocessor which monitors the accumulator state to detect arming, thereby inhibiting deployment when the arming signal is absent. The arming circuit receives the accelerometer signal, removes the dc component which is subject to drift, adds a fixed offset voltage and compares the resultant signal to threshold values to produce an arming signal when a threshold is breached.