car ammeter

A surfeit of circuits has already been published for solid-state car battery voltage monitors. However, no design for a corresponding car ammeter has so far appeared. This design remedies that omission. t--,-..----------------4 o..----►~ Resistor R 1 is a shunt across which is a voltage proportional to the current flowing through it (max 133 m V at 40 A). The voltage drop across this shunt is amplified by differential amplifier A 1 and used to drive a LED voltmeter comprising A2 to AS. With no current through the shunt, Pl is used to set the out- put voltage of Al to nominally 6.5 V, so that the circuit is just on the point of switching over from D4 to DS.