arduino-voltmeter/arduino-sketch.ino

#include <Adafruit_SH110X.h>

#include "version.h"

const long REFERENCE_VOLTAGE_mV = 5000;
const long ANALOG_READ_MAX = 2 << 10 - 1;

const uint8_t DISPLAY_WIDTH = 128;
const uint8_t DISPLAY_HEIGHT = 64;
// https://startingelectronics.org/tutorials/arduino/modules/OLED-128x64-I2C-display/
const uint8_t DISPLAY_I2C_ADDRESS = 0x3C;

Adafruit_SH1106G display(DISPLAY_WIDTH, DISPLAY_HEIGHT);

void setup() {
    // $ stty -F /dev/ttyUSB0 | grep speed
    Serial.begin(115200);
    Serial.println(PROJECT_REPO_URL);
    Serial.println(PROJECT_VERSION);
    if (!display.begin(DISPLAY_I2C_ADDRESS, true)) {
        Serial.println("failed to init display");
        while (true)
            ;
    }
    display.clearDisplay();
    display.setTextColor(SH110X_WHITE);
    display.println(PROJECT_REPO_URL);
    display.println(PROJECT_VERSION);
    display.display();
    delay(2000);
    display.setTextSize(4);
}

void loop() {
    display.clearDisplay();
    display.setCursor(0, 0);
    display.println(
        (long)analogRead(A0) * REFERENCE_VOLTAGE_mV / ANALOG_READ_MAX
    );
    display.print("mV");
    display.display();
    delay(100); // ms
}