Calibrating and averaging

/*
  Voltmeter - calibrated and averaged                    TK09 / /p/tk09

  Wiring. Count from the square pad on the TinkerBlock board, terminal
  at the top, header at the bottom:

    GND    -> GND
    NC     -> nothing   (both NC pins are unconnected on the board)
    SIG    -> A0 on an Uno, GPIO 34 on an ESP32, GPIO 4 on an
              ESP32-S3, GP26 on a Raspberry Pi Pico

  Terminal, same way up: left screw GND, right screw +. DC only, at
  most 25 V on an Uno, about 15.5 V on an ESP32 or ESP32-S3, 16.5 V on
  a Pico. Never mains.

  Arduino IDE
    Tools > Board                 your board, e.g. ESP32S3 Dev Module
    Tools > Port                  the one that appears when you plug in
    Tools > USB CDC On Boot       Enabled   (ESP32-S3 only)
    No library needed.
*/

// The pin SIG is wired to. Uno: A0. ESP32: 34. ESP32-S3: 4. Pico: 26.
const int SIG_PIN = A0;

// Uno: 5.0 and 1023. Pico: 3.3 and 1023. The ESP32s do not use these.
const float VREF = 5.0;
const float ADC_MAX = 1023.0;

const float SCALE = 5.0;   // 30 k over 7.5 k: the terminal is 5 x SIG
const float CAL = 1.000;   // multimeter / sketch, once you have both
const int SAMPLES = 16;    // averaging 16 leaves a quarter of the wander

float sigVolts() {
  float sum = 0;
  for (int i = 0; i < SAMPLES; i++) {
#if defined(ARDUINO_ARCH_ESP32)
    sum += analogReadMilliVolts(SIG_PIN) / 1000.0;
#else
    sum += analogRead(SIG_PIN) * VREF / ADC_MAX;
#endif
  }
  return sum / SAMPLES;
}

void setup() {
  Serial.begin(115200);
}

void loop() {
  float input = sigVolts() * SCALE * CAL;
  Serial.print("input ");
  Serial.print(input, 2);
  Serial.println(" V");
  delay(500);
}

"""
  Voltmeter - calibrated and averaged, MicroPython     TK09 / /p/tk09

  Wiring. Count from the square pad on the TinkerBlock board, terminal
  at the top, header at the bottom:

    GND    -> GND
    NC     -> nothing   (both NC pins are unconnected on the board)
    SIG    -> GPIO 34 on an ESP32, GPIO 4 on an ESP32-S3,
              GP26 on a Raspberry Pi Pico

  Terminal, same way up: left screw GND, right screw +. DC only, at
  most about 15.5 V on an ESP32 or ESP32-S3, 16.5 V on a Pico. Never
  mains.

  Thonny
    Run > Configure interpreter   MicroPython (ESP32) or
                                  MicroPython (Raspberry Pi Pico)
    Save it to the board as main.py to run it on every power-up.
    Nothing to install: machine, sys and time are built in.
"""

from machine import ADC, Pin
import sys
import time

# The GPIO number SIG is wired to. ESP32: 34. ESP32-S3: 4. Pico: 26.
SIG_PIN = 34

SCALE = 5.0      # 30 k over 7.5 k: the terminal is 5 x SIG
CAL = 1.000      # multimeter / sketch, once you have both
SAMPLES = 16     # averaging 16 leaves a quarter of the wander

adc = ADC(Pin(SIG_PIN))

if sys.platform == "rp2":
    def read_once():
        return adc.read_u16() * 3.3 / 65535
else:
    adc.atten(ADC.ATTN_11DB)          # full range; the default is ~1 V
    def read_once():
        return adc.read_uv() / 1_000_000   # calibrated by the firmware

def sig_volts():
    return sum(read_once() for _ in range(SAMPLES)) / SAMPLES

while True:
    print("input {:.2f} V".format(sig_volts() * SCALE * CAL))
    time.sleep_ms(500)