In diesel engines, the air in the cylinders is not hot enough to ignite the fuel under cold conditions. Therefore each cylinder of these engines is fitted with an electric heater known as ‘glow plug.’ A control circuit is necessary to optimise the functioning of glow plugs. It raises the air temperature inside the engine cylinder for quick and reliable starting, extended battery life and reduced diesel consumption. The glow plug controller (Fig. 1) uses a simple timer circuit built around MOSFET T1 for reliability and simplicity. Momentary pushing of switch S2 charges capacitor C1 rapidly via resistor R1. When the voltage on capacitor C 1 exceeds the threshold voltage of the gate (G) of MOSFET T1, it starts charging reservoir capacitor C2 and simultaneously energises relay RL1. MOSFET T1 remains conducting as long as the voltage on C1 is greater than the threshol...