Trigger 12V Relay Using Oxygen Sensor Signal (0.2V-0.8V) at 0.5V Threshold

The discussion addresses triggering a 12V relay using the low voltage output (0.2V to 0.8V) from an automotive oxygen sensor, with a switching threshold around 0.5V to control a small 12V motor. Solutions include using a voltage amplification network to raise the sensor output to a suitable transistor drive voltage, or employing a comparator IC for a clean on/off relay control. Alternatives suggest directly driving a transistor without a comparator, accepting gradual transistor turn-on as sufficient for relay activation. Using germanium transistors or Schottky diodes can help reduce voltage drop and enable switching at lower voltages due to their lower forward voltage compared to silicon transistors. The output impedance of the oxygen sensor is a critical factor in selecting the appropriate interface circuit. For more complex control beyond simple relay triggering, programmable logic controllers (PLCs) such as Maple Systems 7030 units (~$400) are recommended.
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