{"id":81161,"date":"2024-06-04T23:50:09","date_gmt":"2024-06-05T03:50:09","guid":{"rendered":"https:\/\/www.engineersgarage.com\/?p=81161"},"modified":"2024-06-15T01:04:27","modified_gmt":"2024-06-15T05:04:27","slug":"arduino-hx711-digital-weighing-scale","status":"publish","type":"post","link":"https:\/\/www.engineersgarage.com\/arduino-hx711-digital-weighing-scale\/","title":{"rendered":"How to design a weighing scale using Arduino"},"content":{"rendered":"

Weighing scales are frequently used to measure the weight of goods, such as bulk items and raw materials. We sometimes use them at grocery stores to weigh produce or at home to measure our weight.<\/p>\n

Building a weighing scale is no simple task. It involves a combination of load cells<\/a>, amplifier circuits, and microcontrollers or analog-to-digital converters (ADCs). The challenge lies in the calibration, ensuring an accurate scale.<\/p>\n

In this project, we\u2019ll build a single load cell scale using a 1-kg load cell, Arduino, and the HX711 amplifier module. This scale can measure a maximum of 1 kg.<\/p>\n

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After proper calibration, the scale built in this project worked <\/span>perfectly<\/span>, providing the same results as a commercial kitchen scale. <\/span><\/p>\n

Components required <\/span><\/strong><\/p>\n

    \n
  1. Arduino UNO\/Mega x1<\/span><\/li>\n
  2. 1-kg load cell x1<\/span><\/li>\n
  3. HX711 amplifier module x1<\/span><\/li>\n
  4. Push button x1<\/span><\/li>\n
  5. Resistor 330\u2126 x1<\/span><\/li>\n
  6. Load cell kit x1<\/span><\/li>\n
  7. SSD1306 x1 <\/span><\/li>\n<\/ol>\n

    If you do not have a load cell kit, you\u2019ll need to 3D print or build a platform, a plate, and spacers to assemble the load cell into a weighing scale. We\u2019ve used a robot chassis as the platform and a metal cover as the plate. Extra-size bolts are used as spacers. <\/span><\/p>\n

    Assembling the weighing scale
    \n<\/span><\/strong>The first thing to do is assemble the weighing scale. If you have a load cell kit that comes with a platform, plate, spacers, screws, and bolts, your job will be easy. The load cell works by deformation in its strain gauge network.<\/p>\n

    One side of the load cell must be fastened to the fixed platform, and the other side must be fastened to the plate. The spacers are required between the load cell and the platform, as well as the load cell and the plate, to ensure the load cell has enough space to deform when a weight is put on it.
    \n<\/span><\/strong><\/p>\n

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    We’ve used a robot chassis as the platform and a metal cover as the plate. Extra-size bolts are used as spacers.<\/p>\n

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    Calibration
    \n<\/span><\/strong>After <\/span>properly<\/span> assembling the load cell to the platform and plate, it’s time to calibrate it. To do so, find the calibration constant for your load cell. Each load cell outputs its own calibration constant depending upon its design and assembly in the weighing machine. So, it’s necessary to determine its calibration constant.<\/span><\/p>\n

    Calibration circuit connections
    \n<\/span><\/strong>To find the calibration constant, <\/span>interface<\/span> the load cell with the HX711 amplifier module and <\/span>interface<\/span> the amplifier module with the Arduino.<\/span>\u00a0 The load cell has four wires: Excitation + (Red Wire), Excitation \u2013 (Black Wire), Signal + (Green Wire), and Signal \u2013 (White Wire). The HX711 amplifier module is shown in the image below.<\/span><\/p>\n

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    The load module is connected to HX711 according to following table.<\/p>\n

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    Arduino UNO and HX711 are connected according to following table.<\/p>\n

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    The complete circuit connections for proper calibration:<\/p>\n

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    Arduino sketch for proper calibration
    \n<\/strong>After making the circuit connections for the load cell, HX711, and Arduino, upload the below sketch to Arduino.<\/p>\n

    #include “HX711.h”<\/span><\/strong>
    \nconst int HX711_DOUT = 2;<\/span><\/strong>
    \nconst int HX711_SCK = 3;<\/span><\/strong>
    \nHX711 scale;<\/span><\/strong><\/p>\n

    void setup() {<\/span><\/strong>
    \n\u00a0 Serial.begin(115200);<\/span><\/strong>
    \n\u00a0 scale.begin(HX711_DOUT, HX711_SCK);<\/span><\/strong>
    \n}<\/span><\/strong><\/p>\n

    void loop() {<\/strong><\/span>
    \n\u00a0 if (scale.is_ready()) {<\/strong><\/span>
    \n\u00a0 \u00a0 scale.set_scale(); \u00a0 \u00a0<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.println(“Taring…”);<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.println(“Remove any weights from the scale.”);<\/strong><\/span>
    \n\u00a0 \u00a0 delay(5000);<\/strong><\/span>
    \n\u00a0 \u00a0 scale.tare();<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.println(“Tare done…”);<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.print(“Put a known weight on the scale…”);<\/strong><\/span>
    \n\u00a0 \u00a0 delay(5000);<\/strong><\/span>
    \n\u00a0 \u00a0 long x = scale.get_units(10);<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.print(“Result: “);<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.println(x);<\/strong><\/span>
    \n\u00a0 }<\/strong><\/span>
    \n\u00a0 else {<\/strong><\/span>
    \n\u00a0 \u00a0 Serial.println(“HX711 Module not found.”);<\/strong><\/span>
    \n\u00a0 }<\/strong><\/span>
    \n\u00a0 delay(1000);<\/strong><\/span>
    \n}<\/strong><\/span><\/p>\n

    Getting the calibration constant
    \n<\/strong>Open the serial monitor and follow the instructions. At first, ensure the plate is empty to allow Arduino to tare the scale. When prompted, put an item with a known weight on the plate and note the reading.<\/p>\n

    We used a potato that weighed 162 grams on a kitchen scale. The potato readings we received once it was on the plate were 129836, 129827, 129713, and 129734.<\/p>\n

    To get the calibration constant, divide one of the readings from the known weight. For example, a reading of 129836 divided by 162 grams gives a calibration constant of 801.456. After averaging several readings, we received a calibration constant of 800.<\/p>\n

    The calibration code
    \n<\/span><\/strong>The calibration sketch begins by importing Bogden Necula\u2019s HX711.h library. This library handles communication with the HX711 amplifier module. The variables are defined for the pin connections with the HX711 module, and an object of the HX711 class is instantiated. <\/span><\/p>\n

    In the setup() function, the serial monitor\u2019s debug\u2019s baud rate is set to 115200 bps. The HX711 module is initialized by calling the scale.begin() method. <\/span><\/p>\n

    The loop() function determines if the module is ready by calling the scale.<\/span>is_ready() method.<\/span> If it is ready, the scale.set_scale() method is called to set the scale. The user is prompted to remove any weight (the object) on the plate and the scale.tare() method is called to tare the scale. The user is then prompted to put a known weight on the plate. The average of 10 readings (sensed from the HX711) is printed on the serial monitor.<\/span><\/p>\n

    The scale
    \n<\/span><\/strong>Once you have the calibration constant for the load cell assembly, you can complete the construction of the weighing scale. Let\u2019s add a push button and a display unit to the circuit. The display unit used is SSD1306 0.96\u201d OLED.<\/span><\/p>\n

    Circuit connections for the scale
    \n<\/span><\/strong>To build the scale,<\/span> the circuit connections between the load cell and the HX711 and the HX711 and Arduino remain the same. A push button is interfaced at GPIO4 for the tare function. An SSD1306 OLED is interfaced with Arduino UNO, according to the following table.<\/span><\/p>\n

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    The complete circuit connections for the weighing scale are shown in the diagram below.<\/p>\n

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    Arduino sketch for the scale
    \n<\/strong>After making the circuit connections, upload the following sketch to Arduino. Remember to replace the calibration constant with the one for your own load cell assembly.<\/p>\n