Introduction

This tutorial will teaches you how to build a weighing machine with the Arduino using a load cell and the HX711 amplifier. First, you’ll learn how to wire the load cell and the HX711 amplifier to the Arduino to build a Weighing Machine. Then we’ll show you how to calibrate the scale and use it to calculate the weight of objects. We’ll also add a display to show the measurements in LCD.

Bill Of Materials

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SN	COMPONENTS NAME	DESCRIPTION	QUANTITY
1	Arduino Board	Arduino UNO R3 Development Board	1	https://amzn.to/3UBnwTO
2	LCD Display	16x2 LCD Display	1	https://amzn.to/3UhShNH
3	Potentiometer	10K	1	https://amzn.to/3NMyzag
4	Load Cell	1Kg-40KG Load Cell	1	https://amzn.to/3U8I329
5	HX711 Module	24 Bit Precision Amplifier for Load Cell	1	https://amzn.to/3zT6IzN
6	Push Buttons	Push-To-ON Reset Tact Switch	1	https://amzn.to/3DP2V7J
7	Connecting wires	jumper wire	some	https://amzn.to/3fMoSw7
8	Breadboard	Normal	1	https://amzn.to/3FUQlXe

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What is Load Cell

A load cell is a transducer that converts a force into electrical signal that can be measured. The electrical signal changes in proportion to the applied force. Load cells come in three varieties: strain gauges, pneumatic, and hydraulic. We’ll go over strain gauge load cells in this tutorial.

A strain gauge is a sensor that changes its resistance depending on the pressure exerted on it due to the piezo resistive effect.

Bar Load Cells

A bar load cell contain four strain gauges already in a Wheatstone bridge.

The white blobs at the top and bottom each have two strain gauges. The object to be weighed is placed on the bar’s edge (the one far from the wire). This elongates the strain gauges at top and compresses the ones at the bottom.

If the load cell has weight, a voltage will exist in the white and green wires. Then again, due to infinitesimal change in the resistance, this voltage is still very small and cannot be fed to micro controller directly. So, here we need a amplifier circuit that converts a small signal to required signal that can be read by analog pin of micro controller.

HX711 Amplifier

The output signal produced by the load cell is in range of millivolts, so we need an amplifier to convert the signal into a level that we can later transform it into a digital signal and process it. For this purpose, we useHX711 amplifier sensor. The HX711 amplifier sensor includes a HX711 chip with analog-to-digital conversion capability in 24-bit accuracy. The HX711 module amplifies the low-voltage output of the load cell and sends it to the Arduino so that the Arduino eventually calculate weight from this data.

Wiring Load Cell and HX711 Amplifier

Circuit Diagram: Interfacing HX711 Load Cell with Arduino

Working Principle

First of all we must place a known weight on our load cell.Then, do the calibration with the raw value displayed at serial monitor. Now, You can place any object on load cell which weight is unknown to you. The output of load cell will be in mili volt so its output is feed to amplifier and analog to digital converter before providing to...