Arduino Hx711 Weight Scale Interface 1 0 Software
OVERVIEW We’ve all used a scale to determine the weight of something at some point in our lives. Using a Load Cell or Weight sensor you can add this capability to your Arduino projects. In this tutorial we will see how to connect, calibrate and display the weight on a small OLED display, and by using a rotary encoder we will be able to change the units from: grams, kg or pounds. We will be using the HX711 ADC converter board to amplify the signal received from the weight sensor. This amplifier enables the Arduino to detect the changes in resistance from the load cell. Load Cell and HX711 INTRODUCTION So what is a Load Cell?
They are many types of Load Cell, but today we will be using the straight bar type. When pressure or a load is applied, the electrical resistance will change in response to this applied pressure and by taking this information and after some calibration we can determine the precise weight. Load cell like this one come in different weight limits, the one we will be using today is rated up to 1KG, but you can get others that will support more weight if needed.
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Also the ADC on the arduino is 10 bit which provides a maximum of 2^10 ie. 1024 readings compared to HX711 which is 24 bit ADC and easy to interface. HX711 Datasheet. The Hx711 uses SPI interface to communiacate to the Arduino. (Refer Data sheet for more info) More info on DfRobots. Connecting to Arduino. Connection is pretty simple.
What about this HX711? The changes in electrical resistance provided by the Load Cell need to be amplified so that they can be read by an Arduino. That’s exactly what the HX711 board does. It reads the information from the Load Cell, amplifies the signals and then sends it to the Arduino for processing.
Common Load cells have four-wire to connect the HX711 to a microcontroller like the Arduino. • Red (VCC) • Black (GND) • Data • Clock To connect the HX711 to the Arduino you only need 2 pins (Clock and Data). On the opposite side you can see the connection for the Load cell. We will be using a simple Arduino library to communicate with the HX711 that provides a calibration and Tare (reset) feature to easily determine the weight of an object. LOAD CELL SETUP The bar type we are using has different screws holes on the bottom and the top. To it up as a scale, you attach the bottom left or right screw holes to a table or stable object, and then attach a piece of platic or any other material to serve as the scale to put objects on, to the top opposite screw holes.
*Each bar type has an arrow that indicate the direction of deflection and should be positioned the correct way for your project. You can see a simple setup here: This setup is for using the Load Cell has a simple scale, but you could also connect it the detect deflection between two object if you wanted. CONNECTIONS The connections for this tutorial are pretty straightforward: The 5V and GND of the UNO is connected to each modules VCC and GND.
Since the OLED display uses I2C we are using pins A4 (SDA), A5 (SCL) on the UNO to connect it. The rotary encoder is connected to these pins: CLK to pin 2, DT to pin 3 and SW to pin 4. The HX711 is connected to: DATA to pin 4 and CLOCK to pin 5. Depending on the HX711 your purchase it may have different connections: If it has color designation, then connect the corrresponding wires from the Load Cell to the HX711. In my case my HX711 had these connections: E+: Connected to RED of the Load Cell E-: Connected to BLACK A-: Connected to GREEN A+: Connected to WHITE B-: no connections B+: no connections. THE CODE We are using a library written for the HX711 to communicate with the Arduino, you can find a link to download the library at the bottom of this page.
The first code is used to get the calibration factor for a particular Load cell, this will have to be run for each Load Cell you own, since each one is a little different. The second code uses that calibration factor to print out the correct weight on the OLED display. As always for more information please have a look at the tutorial video.
Precision scale base based on HX711 and VFD display This is a simple precision scale project that employs a cool VFD display. The display is connected to the Arduino by asynchronous serial interface 57600 allowing a satisfactory fast data refresh. The HX711 uses pins A0 and A1 of the Arduino for the communication and provides the power supply for the load cell. Be advised that HX711 is quite sensitive to power supply fluctuations that affects the output signal; a high stability power supply will improve the overall precision of the scale. User interface The user interface is very simple and provide readings in Newtons, grams and ounces; I've also implemented an analog bar graph showing the load in% of full scale. A push button is providing the zero (tare) function of the scale. BOM • 1 x NORITAKE VFD display mod.