Oxygen (O2) sensors are used to sense the amount of oxygen in the exhaust gases. The following circuit uses two LM3914s Dot/Bar Display Driver IC for the LED display. This O2 sensor circuit will be used as air fuel mixture meter of cars.
sensor operates at 5V regular supply, uses 1/4 Watt 1K resistors, 10V
2.2 or 4.7 uF filter capacitor and 0.95V potentiometer on pin 6 of LM3914
which will cause the last LED to turn on when the input from the sensor
exceeds 0.95V. To prevent over voltage of the battery, it uses
regulator which also has an internal thermal sensing circuit that limits
the current output to avoid damaging the regulator.
Detailed explanation on 5V O2 Sensor Circuit using LM3914 LED Display for Car Air-Fuel Mixture Meter can be seen here in the pdf filetype (source: buckeyetriumphs.org)