Design and Implementation of a Combinational Vehicle Engine Monitoring System with Don't-Care Conditions and an Automatic RPM Limiter

This work presents the design, simplification and experimental verification of a combinational circuit thatmonitors the operating regime of a vehicle engine and triggers an audible alarm when the engine works underdangerous conditions. The system has four binary sensors (engine speed, oil pressure and two water-temperaturethresholds) and four don’t-care conditions, since the two temperature sensors can never give contradictory readings.The alarm function was derived from a truth table, simplified with a four-variable Karnaugh map, S = P + T9 +R·T8, and also obtained from the canonical sum of products, simplified algebraically to S = P·T9' + T8·T9 + R·T8.Both expressions agree on all twelve feasible input combinations. The Karnaugh-map circuit, which needs only oneAND gate and one three-input OR gate, was assembled on an Exsto XD201 educational kit, and the observedoutputs matched the predictions for all sixteen input combinations. As an improvement, a second output L =R·T8·T9' was added to drive an automatic engine-speed limiter when the water is between 80 °C and 90 °C and theengine is above 2,000 rpm; this reuses the existing R·T8 signal and adds only one NOT and one AND gate. Theextended circuit was also built and verified experimentally on all sixteen combinations.