Engine-Position Inputs

Purpose

This module defines the dedicated crank and cam position-input class for NeoECU V1. It is separate from the generic digital-input module because engine timing needs bounded edge delay, jitter, and false-trigger behaviour.

This is an architecture and schematic-design basis, not a released schematic. Final component values and qualified fault ratings require the selected sensor, harness, connector, and test results.

V1 timing and signal assumptions

Signal	V1 arrangement	Function
Crank	Two events per crank revolution	180-degree position events and speed estimation
Cam	One event per 720-degree cycle	Four-stroke phase identification

The V1 speed limiter is 5,000 RPM. At that speed the interval between selected crank events is 6 ms; a four-event-per-revolution trigger would instead have a 3 ms interval. V1 retains the two-event pattern. Moving to four events is a future trigger-wheel and firmware change, not a reason to alter this input class.

The intended interface is a three-wire, active-low Hall sensor: the output is normally high and sinks current while active. Capture one defined edge per event, normally the falling edge, in an STM32H747 timer channel. Do not use both edges as independent position events unless firmware explicitly models the Hall-window geometry.

FEBI BILSTEIN 44421 is the selected cam sensor. It cross-references to EFI Automotive 144321 and OE references 1920.6T and 9629684380. It is a three-wire 12 V Hall sensor with an open-drain output: supply it from +12V_SENS, connect its return to SENSOR_GND, and pull its signal high at the ECU. Confirm the physical connector pinout and output sink-current limit from the delivered part or its manufacturer documentation before assigning the connector pins and freezing R_PULLUP. The crank-sensor part number remains to be selected.

Electrical interface

Supply the sensor from +12V_SENS; its rail generation, protection, current limit, and diagnostics belong to POWER_ARCHITECTURE.md.
Place the signal pull-up at the ECU, to +12V_SENS, rather than at the sensor or 3.3 V domain. A 4.7 kOhm footprint is a starting provision only. Select its value from the confirmed sensor sink-current rating, high/low thresholds, cable capacitance, and required edge time.
Protect the connector-side signal against the assigned positive and negative harness transients. The completed clamp, series impedance, divider, and Schmitt buffer must keep all intermediate nodes within their validated limits without back-powering the 3.3 V rail while the ECU is off.
Scale the high-level signal before the 3.3 V Schmitt buffer. The buffer provides defined logic thresholds and hysteresis; the STM32 pin is never exposed to the sensor-domain voltage.
The divider also supplies the resistance for the RC filter. Connect the configurable C_FILTER footprint from the divided signal to SENSOR_GND, in parallel with R_DIV_BOTTOM. Its effective series resistance is R_DIV_TOP || R_DIV_BOTTOM, so tau = (R_DIV_TOP || R_DIV_BOTTOM) * C_FILTER. Do not add a separate RC series resistor by default. Add one only if it has a separately demonstrated purpose, such as limiting residual-clamp current.
Populate 1 nF initially, with 470 pF and 2.2 nF alternatives available. Validate the selected value with the final harness and ignition operating; it must reject short interference without eroding legitimate-edge timing margin.
Use the automotive-qualified SN74LVC2G17QDCKRQ1, powered from +3V3_MAIN, as the two-channel non-inverting Schmitt buffer for crank and cam. Its inputs must only receive the protected, divided signal, never the raw 12 V harness node.

Connector, harness, shield, and layout

Crank and cam use the dedicated engine-sensors connector, not the power/actuator connector. This preserves physical separation from coil, injector, starter, and other high-current wiring. The V1 connector plan is:

Connector group	Carries
Power/actuators	Battery and power returns, ignition, injector, and high-current outputs
Engine sensors	Crank/cam supply, signals, sensor returns, thermistors, and analogue sensors
Vehicle I/O/CAN	CAN, deadman, generic digital inputs, and generic 5 V logic outputs

Use a screened harness for each trigger sensor. Route the trigger signal as a twisted pair with SENSOR_GND; route its +12V_SENS supply in the same screened cable. The screen is an EMC structure, not a sensor return or circuit ground conductor.

Terminate each screen at the ECU end only, at a dedicated SHIELD_GND bond with a short, broad connection to the enclosure/chassis structure near the power-entry region. Do not connect the screen to SENSOR_GND, DGND, or +3V3_ANA, and do not connect it at the sensor end. Final backshell and case bonding details depend on the selected connector and enclosure.

Place transient protection at the connector. Keep the divider, filter, Schmitt buffer, and timer route on the quiet MCU side. Keep these paths away from the ignition high-voltage node, injector switching loop, and regulator hot loops.

False-trigger handling and validation

Hardware filtering is the first defence. Firmware provides a second, independent plausibility check; it does not replace the hardware network.

For every selected crank edge, firmware shall:

timestamp the edge with the timer;
reject an edge whose interval since the previous accepted edge is below a calibrated physical minimum; and
reject an interval that implies an implausible acceleration from the recent accepted speed estimate.

The threshold shall be derived from the maximum measured engine acceleration, the 5,000 RPM speed limit, timer resolution, and a conservative margin. It shall not be a fixed arbitrary debounce time. A rejected edge shall not update speed, position, dwell, injection scheduling, or the reference interval, so a spark-induced pulse cannot displace the next accepted timing event.

Cam edges shall be checked against the expected crank phase. A missing or inconsistent cam event removes phase synchronisation and must lead firmware to the explicitly defined no-sync behaviour; it must never invent a phase from a single unexpected edge.

Validate with the installed engine and final harness:

no false accepted crank/cam events during worst-case dwell and spark;
no missed genuine events at 5,000 RPM and during the maximum measured acceleration;
measured conditioning delay and jitter within the firmware timing budget;
correct rejection of injected short glitches without corrupting the following genuine event; and
sensor unplug, signal open/short, and sensor-supply fault behaviour as defined by the final selected parts.

Remaining inputs before schematic freeze

Confirm the FEBI 44421 physical connector pinout and output sink-current limit from the delivered part or manufacturer documentation.
Select and obtain the equivalent data for the crank sensor.
Confirm connector family, pin assignment, cable length/construction, and enclosure/backshell method for the engine-sensors connector.
Select protection components and final pull-up, divider, and filter values against the confirmed sensor and harness limits.
Measure maximum real engine acceleration and establish the timer-based interval-plausibility limits in firmware.

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