🛠 Lire l'ADC 12 bits et le capteur de température interne du RP2350

Objectives

The RP2350 features a 12-bit SAR ADC, 500 kSPS, with 4 channels on the RP2350A / 8 on the RP2350B, plus an internal temperature channel — but no DAC (RP2350 datasheet). Official SDK examples map ADC channels 0..3 to GP26..GP28. This tutorial covers reading an external voltage with a potentiometer, reading the core temperature, and properly handling the RP2350 ADC's 12-bit scale (0..4095).

Hardware

• 1 × generic RP2350 board + MicroPython rp2 (RP2350 firmware)
• 1 × 10 kΩ potentiometer: pin 1 → 3V3, pin 3 → GND, wiper → GP26
• 3 × wires; no resistor needed (the ADC accepts the source directly)
• For temperature: just place your finger on the chip 😉

Full Code

# adc_temp.py — ADC0 (GP26) + canal température interne
from machine import ADC, Pin
import time

# Canal 4 = capteur thermique interne (comme sur RP2040)
sense = ADC(4)
# ADC0 : sur le port rp2, ADC(0) cible l'entrée analogique ADC0 = GP26
pot = ADC(0)

REF = 3.3            # pleine échelle = alimentation IO, ici 3,3 V
FULL = 4095          # l'ADC du RP2350 est nativement 12 bits

def tension(adc):
    return adc.read * REF / FULL        # read = valeur brute 12 bits

def temperature:
    v = tension(sense)
    # formule datasheet famille RP2 : 0,706 V à 27 °C, pente -1,721 mV/°C
    return 27.0 - (v - 0.706) / 0.001721

while True:
    print('pot: %4d  %.3f V   coeur: %.1f C'
          % (pot.read, tension(pot), temperature))
    time.sleep_ms(500)

Expected Verification

Turn the potentiometer: the raw value follows 0 → 4095 and the voltage 0 → 3.3 V linearly. Place your finger on the RP2350: the core temperature rises by a few degrees in a few seconds, then drops back down. The formula 27.0 - (v - 0.706) / 0.001721 is the one for the RP2 family (sensor voltage 0.706 V at 27 °C, slope 1.721 mV/°C) — it gives the core temperature (internal diode), not the ambient temperature: 30–35 °C when held in hand is normal.

Common Errors

• Confusing read (raw, 0..4095 on this 12-bit chip) and read_u16 (rescaled to 16 bits by MicroPython): choose ONE scale and divide by the correct full scale — a factor of 16 error isn't always obvious.
• Measuring the temperature channel as a normal input: the internal channel is not linear with input voltage, use the dedicated formula.
• Using ADC0 on a pin other than GP26: ADC channels are fixed to the analog pins (GP26..GP28 according to SDK examples), unlike UART/SPI/I2C which can be routed anywhere.
• IO supply at 1.8 V: the ADC full scale follows the IO supply — if your setup uses 1.8 V IOVDD, adjust REF.
• Source impedance too high (> 10 kΩ): the internal sampler discharges, values become noisy — the 10 kΩ potentiometer is a reasonable upper limit.
• Expecting an analog output: the RP2350 has no DAC; for a variable voltage, use PWM + an RC filter (the RP2350's 8/12 PWM slices will do the job).
• Targeting channels 4..7 on an RP2350A board: the 8 channels only exist on the 48-GPIO silicon (RP2350B) — check the chip variant, not just the module format.
• Leaving inputs floating: on A2 chips, a floating input can drift towards 2.2 V due to Bank 0 leakage (errata E9) — connect or configure your unused pins.