Ph

The ph module reads a pH probe. It defines a hardware-agnostic PhProbe trait and ships one implementation, AnalogPhProbe, that samples a probe’s analog output through the ESP32-C3’s ADC. The trait lets the rest of the system read pH without knowing how the probe is wired up.

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The PhProbe Trait

PhProbe is the abstraction every probe implements:

Method	Meaning
read()	Take a reading. async, fallible (Result<Float, Self::Error>).

read is async so that probes talking to a chip over a bus can await their I/O; the analog implementation drives the ADC and resolves once the conversion completes.

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AnalogPhProbe

The analog probe is built from the ADC1 peripheral and the GPIO carrying the probe’s analog output:

let mut probe = AnalogPhProbe::new(peripherals.ADC1, peripherals.GPIO0);

On the ESP32-C3, GPIO0 is ADC1 channel 0. The pin is enabled at 11 dB attenuation so the ADC covers the widest input range the chip offers.

Calibration

The pin is enabled with the AdcCalCurve calibration scheme:

config.enable_pin_with_cal::<PIN, AdcCalCurve<ADC1>>(input, Attenuation::_11dB);

This is not optional polish — it is required for correct readings. The calibration scheme sets the ADC’s zero-bias init code from the chip’s eFuse and returns the result in millivolts via curve fitting.

Sampling

read does not return a single conversion. It takes 16 samples, discards the single highest and lowest, and averages the remaining 14:

let avg = (sum - min - max) / (SAMPLES - 2);

Averaging cuts the ADC’s random noise by roughly √N, and dropping the extremes rejects the occasional outlier spike — most visible while Wi-Fi is transmitting, which couples noise into the ADC. pH changes slowly, so the cost of 16 conversions per reading is irrelevant.