Vehicle Speed Sensor Circuit Schematic - LM2917N VSS for Traction Control/EMS

This document is a screenshot of a Vehicle Speed Sensor (VSS) circuit schematic built around an LM 2917N frequency-to-voltage converter IC, intended for a wheel-speed / traction control application feeding an EMS (engine management system) input. The circuit runs on +12V, uses an IN4148 diode, 10K and 100K resistors, a 470R resistor, a 6.2V Zener, a 2.2uF tantalum capacitor, a variable resistor VR1, and outputs a speed signal to a de-coupler; a red hand-drawn annotation shows a 5V pull-up and 10K resistor feeding the EMS input. Notes state this is for the driven circuit only, and that two identical circuits are needed — one for a sensor on the driven wheel/drive shaft and one for the undriven wheel. Design formulas are given (Vout = Vin x Fin x C1 x R1) with an example of 32 pulses per 2 meters giving 715 Hz at 100 MPH, plus recommended C1 values (15nF, 6.8nF, or 3.3nF depending on pulses per 2 meters) and RV1 = 500K set for 2.5V at half max speed. A suggested sensor is the Omron E2EL-X2E1-DSL-2M (RS stock No. 378-8191) with wiring: Black = signal, Blue = 0V, Brown = +12V. A note explains how the code compares driven and undriven wheel speeds to trigger traction control via ignition retard and other power-reduction methods.