This circuit is designed to display the output from an O2 sensor. It can be easily be calibrated to work with 1v or 1.25v O2 sensors.

To calibrate the circuit supply it with 12v then use another power source ie: 1.5v battery, a suitable virable resistor (Rc) and a voltmeter. The –ve of the battery goes to –ve of the O2 display and the +ve goes to Rc then from Rc to the O2 display input. Connect the +ve lead of the voltmeter to the O2 display input and the –ve lead to the adjust Rc untill you have 1v (or 1.25v depending on the sensor) showing on the voltmeter, now turn R1 until all of the LED’s have just come on.