Shut down the engine if the driver applies throttle and hard braking at the same time, or if a throttle or brake sensor fails. Required to run electronic throttle control.
Throttle position and brake pressure signals pass through voltage dividers into linear comparators. Comparator outputs feed OR gates: one detects either throttle position above 10%, the other detects either brake pressure above the hard braking threshold (600 psi, roughly 4.14 MPa, on the CR22 design). The OR outputs feed an AND gate, so the fault only registers when both are true. The AND output passes through a delay chip setting a 1 second delay, then into an SR latch. The latch drives MOSFETs, driven at 12 V on the collector with the emitter wired to three normally-open automotive relays controlling the throttle body, fuel system and ignition system.
Designed in Altium so the PCB layout can be pushed to MCAD, which is how the enclosure was designed alongside the board. Split into main connector, reset subcircuit, signal loss subcircuit, simultaneous brake and throttle subcircuit, and fault and latching subcircuit.
Rules define the required behaviour and the response time. The signal loss requirement is what took the design to a third revision. An ETC Rules Exception question had to be submitted and accepted before the ETC Review Form was approved.
Validated on the car by logging MoTeC PDM outputs: output 1 (ignition supply), output 11 (fuel injector supply) and output 5 (fuel pump supply) all drop for the 1.002 s fault duration when heavy braking above 600 psi and more than 10% throttle are detected. A separate case validates PDM behaviour on TPS1 signal loss.
PCB manufactured externally, populated and tested in house. Case designed from the Altium ECAD-to-MCAD push.
From the cost report drawings: Polyethelyne (BSPD).
Rules compliance on sensor loss is the recurring problem. CR22's Rev 2 board was in the car but not fully rules legal, and when fully tested did not meet the sensor loss requirement. It took to Rev 3 to close out. Board turnaround between revisions is a real schedule risk: Rev 1 August 2023, Rev 2 January 2024, Rev 3 March 2024. An ETC Rules Exception question had to be submitted and accepted before the ETC Review Form was approved. The 2020 board's changelog records the specific defects found in review, which are worth reading before laying out a new revision: a mirrored relay footprint; comparators that had to be powered at 12 V because they only work with the reference at Vcc minus 2.0 V, which left the TPS2 comparator and the check-if-high comparators non-functional; a missing N-MOSFET NOT gate on the latch output with relay polarity switched so the relays are off unless the board is on; a redundant parallel resistor on the relay MOSFETs; a 1k resistor that had to become 10k because it was pulling the latch output too low to trigger the relays; a reversed TPS2 comparator polarity; and the 1 second delay needing oscilloscope verification. Layout defects from the same review: no close ground path to the 555 bypass capacitors, a 90 degree trace, traces and components too close to the board edge to fit a case, motor relay trace too small to carry the current, 6 mil spacing too tight against manufacturer error, and internal traces used where power and ground planes were needed.
Revision 3 addressed the sensor loss rules requirement that Rev 2 failed. The 2020 changelog's layout lessons carry forward: power and ground planes instead of internal traces, wider than 6 mil spacing to avoid manufacturer error, traces and components kept away from the board edge so a case fits, and a wider motor relay trace.
Dimensions called out on the cost report drawings. These are the figures printed on the drawing, not a labelled specification; open the drawing itself for what each one refers to. BSPD (mm): 107.5, 28.4, 113.9, 74.3, 3.2, 134.2, 34.8, 14.5, 10.2 41.2, 27.3 Source: Cost report drawings: CR26i/Document Submissions/Cost Report/Instruments, Wiring & Accessories/ECM_Engine Electronics Assembly/BSPD.PDF Quantity per car, as costed: 1