Create an Arduino Uno Voltmeter with OLED Graphic Output

Build a handy pocket diagnostic tool. Learn how to read analog voltage inputs and render them visually.

Introduction & Concept

Arduino ADCs are rated for a maximum of 5V. To measure voltages up to 25V, we must implement a voltage divider circuit. By utilizing two resistors, the divider drops the measured potential proportionally. The microcontroller calculates the true source voltage mathematically and plots the value onto a 0.91" OLED display.

Components Needed

Component Name	Store Link
0.91 OLED Screen	Buy 0.91 OLED Screen

Circuit Divider Schematic

   V_IN (+) ---> [ 100k Ohm ] ---+--- [ 10k Ohm ] ---> GND (-)
                                 |
                                 +---> Arduino Analog Input A0
          

Control Code

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 32
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

const float R1 = 100000.0; // 100k
const float R2 = 10000.0;  // 10k

void setup() {
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextColor(WHITE);
}

void loop() {
  int value = analogRead(A0);
  float vout = (value * 5.0) / 1023.0;
  float vin = vout / (R2 / (R1 + R2));
  
  display.clearDisplay();
  display.setCursor(0,0);
  display.print("Voltmeter Node");
  display.setCursor(0,16);
  display.print("Voltage: " + String(vin) + " V");
  display.display();
  delay(500);
}