This very simple automotive device will allow you to monitor the fuel mixtures being run by your car. This type of sensor is also known as an EGO (Exhaust, Gas, Oxygen) monitor. You can use it as a tuning tool, to help with vehicle modification or simply to see the behaviour of the engine control unit. Indication is via 10 LEDs to display mixture concentrations from rich to lean. The circuit connects to the EGO sensor mounted in the exhaust manifold and is powered the vehicle's 12 volt battery.