O2 sensor signal converter. Analog input 100mV to 900mV amplified to max 12v (car battery voltage).
Amplifiers are configured as comparators using transistor-based voltage regulators as low reference.
At analog minimum, Air/Fuel mixture is very lean, causing the bottom right Red "Over Lean" light to illuminate. At analog maximum, the lower left Yellow "Over Rich" light illuminates.
In between maximum and minimum input, comparator circuits illuminate only the LED associated with preset voltage range set by diode breakdown voltage in regulator circuits.
