The European Rover Challenge (ERC) includes an Astrobiology and science task as part of its competition. For these tasks, we’ve developed a custom sensor board, which is equipped with multiple sensors to perform environmental and chemical analysis. This board is fully compatible with our newly developed sensor network, WECANT, which we introduced in the blog post “WECANT Sensor Network”.

pH Measurement with external Electrodes

One of the main features of our board is a pH sensor module. It is designed to interface with an external pH electrode. These electrodes generate a small, linearly varying voltage depending on the pH level of the fluid being measured. At pH 7, the voltage is around 0V. Therefore, acidic, and basic solutions are causing a shift in either the positive or the negative direction. Our system uses a 12-bit ADC with an input range of 3.3V. Our ADC can therefore not directly measure negative voltages. Due to that we’ve implemented an analog differential amplifier that serves two key roles:

• Gain control: Amplifying the small voltage signal to match the 3.3V input range of the ADC.
• Offset adjustment: Shifting the signal 1.65V into the ADC’s measurable range as the ADC cannot measure negative voltages.

Since the voltage output of a pH electrode is temperature-dependent, temperature variations can significantly affect measurement accuracy. To perform temperature compensation, we’ve integrated support for PT100 and PT1000 temperature sensors. This ensures that the pH values reflect true chemical conditions, even when the temperature changes. For calibration, we use standard buffer solutions with pH levels of 4, 7, and 9. These calibration points allow us to reliably measure pH levels across the relevant range with good accuracy.

Additional environmental sensors

In addition to the pH and temperature sensors, our sensor board is equipped with several other environmental sensors to provide a comprehensive data set for the science task:

• Barometric pressure sensor

• Magnetic field sensors
• Ambient temperature and humidity sensors

These sensors collect important environmental data that support the chemical information from the pH sensor, allowing for a more complete analysis during the ERC mission.

We will continue to share updates of our rover as we advance toward the ERC. Stay tuned!