This project aims to design a low-cost wideband oxygen-sensor controller for accurate lambda measurement. The system regulates heater temperature and maintains the Nernst cell voltage at 450 mV using a pump-current loop. The required pump current is measured to determine lambda.
This project presents a low-cost wideband sensor controller that maintains the sensor’s Nernst cell voltage (Vs) at 450 mV and regulates heater temperature to ensure accurate lambda (air-fuel ratio) measurement. The system uses two coordinated control loops: a fast pump-current loop that drives a DAC to correct deviations in Vs, and a slow PID loop that stabilizes the sensor’s internal heater at its required operating temperature.
A dedicated amplifier stage provides a measurable voltage proportional to the pump current (Ip), enabling the controller to calculate the lambda value directly from the circuit’s output. By continuously comparing Vs to its 450 mV target and adjusting Ip in real time, the system replicates the functional behavior of commercial wideband controllers in a simplified, accessible implementation.
The design leverages the ESP32’s ADC and DAC resources, efficient sampling methods, and stable closed-loop operation, allowing reliable performance across different operating conditions while maintaining consistent Vs and accurate pump-current measurement.
