Overview
The Brake System Plausibility Device (BSPD) is a non-programmable safety circuit I designed for the University of Manchester's Formula Student car, built entirely in discrete logic with no microcontroller in the fault path. It monitors the throttle and brake sensors in real time and cuts power to the vehicle if it detects an implausible condition, such as the brake and throttle being applied simultaneously or a sensor signal going out of range.
The BSPD continuously monitors the throttle position sensor (TPS) and brake pressure sensor (BPS) on the car, watching for two independent fault conditions. The first is a plausibility check: if the brakes are applied while the throttle reads more than 25% above idle, and both hold true for over 500 ms, the circuit cuts power to the vehicle, since a car should never be significantly on-throttle and on-brake at the same time. The second is a sensor integrity check: if either sensor's signal falls outside the expected 0.5 to 4.5 V range for 500 ms, indicating a wiring fault or sensor failure, power is cut as well. Because competition rules require this kind of safety-critical monitoring to run without a microcontroller in the fault path, the entire circuit is built in discrete logic rather than software, and power only resets automatically after a full 10 seconds passes with no fault present.
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