Arduino Scale with LCD

Overview

If you learned on an Arduino Uno or Nano, this project is for you. The ET-M08 is a 5 V, 16 MHz ATmega328PB board that works with the Arduino IDE, and its 5 V Qwiic port drives a standard 16×2 character LCD through the ET-D10 backpack.

The ET-S67 HX711 amplifier reads a bar load cell with 24-bit resolution. The ET-A20 pad gives you tare, units and calibrate buttons, and the calibration is saved in the microcontroller's EEPROM.

• Reads in grams or ounces
• Tare, units and one-button calibration
• 16×2 LCD with backlight
• Calibration saved in EEPROM

What you need

ElectroTrical boards

ET-M08ATmega328PB Nano-Style Board5 V Arduino-compatible controller

Coming soon

ET-S67HX711 Load Cell Amplifier24-bit load-cell amplifier

Coming soon

ET-D10I²C Character LCD BackpackRuns the LCD from two wires

Coming soon

ET-A204-Button PadTare, units and calibrate

Coming soon

You'll also need

• 16×2 character LCD (HD44780, 5 V)
• Bar load cell, 4-wire (1 kg or 5 kg)
• Two rigid plates and screws with spacers
• A known weight for calibration (e.g. 500 g)
• 1 Qwiic cable, jumper wires

Wiring

The ET-M08 runs at 5 V, so everything here is 5 V. Don't connect 3.3 V-only boards to its Qwiic port without the ET-A09 adapter.

Build it

1. 01

   Build the scale

   Screw the load cell between the two plates with spacers so it can flex, arrow pointing down. Only its end blocks may touch the plates.

2. 02

   Fit the LCD backpack

   Solder the ET-D10 to the back of the LCD. After the first upload, turn its contrast trimmer until the characters are clear.

3. 03

   Set up the Arduino IDE

   Add the MiniCore URL (https://mcudude.github.io/MiniCore/package_MCUdude_MiniCore_index.json) in Preferences and install MiniCore. Select board “ATmega328”, Variant “328PB”, Clock “External 16 MHz”, then the board's COM port.

4. 04

   Calibrate

   Upload, empty the scale and press B1 (tare). Put your known weight on, press B3, and the scale saves the factor. Change CAL_GRAMS in the sketch if your weight isn't 500 g.

5. 05

   Weigh

   B1 tares, B2 switches between grams and ounces.

Arduino code

Written for the ET-M08 ATmega328PB Nano-Style Board. Install these libraries from the Arduino Library Manager:

• HX711 Arduino Library by Bogdan Necula
• LiquidCrystal I2C by Frank de Brabander

#include <Wire.h>
#include <EEPROM.h>
#include <HX711.h>
#include <LiquidCrystal_I2C.h>

const int DOUT = 2, SCK_PIN = 3, B_TARE = 4, B_UNIT = 5, B_CAL = 6;
const float CAL_GRAMS = 500.0;

HX711 scale;
LiquidCrystal_I2C lcd(0x27, 16, 2);
bool ounces = false;

bool pressed(int pin) {
  if (digitalRead(pin) == LOW) { delay(30); while (digitalRead(pin) == LOW); return true; }
  return false;
}

void setup() {
  pinMode(B_TARE, INPUT_PULLUP); pinMode(B_UNIT, INPUT_PULLUP); pinMode(B_CAL, INPUT_PULLUP);
  lcd.init();
  lcd.backlight();
  lcd.print("ElectroTrical");
  lcd.setCursor(0, 1); lcd.print("Scale starting");

  scale.begin(DOUT, SCK_PIN);
  float factor;
  EEPROM.get(0, factor);
  if (isnan(factor) || factor == 0) factor = 420.0;   // rough default until calibrated
  scale.set_scale(factor);
  scale.tare(20);
  lcd.clear();
}

void loop() {
  if (pressed(B_TARE)) { lcd.clear(); lcd.print("Tare..."); scale.tare(20); lcd.clear(); }
  if (pressed(B_UNIT)) ounces = !ounces;
  if (pressed(B_CAL)) {
    lcd.clear(); lcd.print("Calibrating...");
    scale.set_scale();                                // factor 1
    float raw = scale.get_units(20);
    float factor = raw / CAL_GRAMS;
    scale.set_scale(factor);
    EEPROM.put(0, factor);
    lcd.clear(); lcd.print("Saved"); delay(800); lcd.clear();
  }

  float g = scale.get_units(5);
  lcd.setCursor(0, 0);
  lcd.print("Weight:         ");
  lcd.setCursor(0, 1);
  if (ounces) { lcd.print(g / 28.3495, 2); lcd.print(" oz        "); }
  else        { lcd.print(g, 1);           lcd.print(" g         "); }
  delay(200);
}

Troubleshooting

Take it further

• Add the ET-A16 buzzer to beep at a target weight
• Count identical parts by weight
• Log weighings to the ET-C06 microSD board