Sparkfun HX711 Manuale utente

Load Cell Amplifier HX711 Breakout Hookup

Guide





Getting Started

The HX711 load cell amplifier is used to get measurable data out from a

load cell and strain gauge. This Hookup Guide will show you how to get

started with this amplifier using some of the various load cells we carry at

SparkFun.

What You Will Need:

For this simple hook up guide we will just be hooking up a load cell with the

HX711 amplifier, and showing how you would hook up four load sensors

with a combinator board and the HX711 amplifier. To follow along, you’ll

need:

• SparkFun Load Cell Amplifier - HX711

• Any Strain Gauge Based Load Cell:

Load Cell - 200kg, Disc

(TAS606

)



SEN-13332

Load Cell - 50kg, Disc

(TAS606)

SEN-13331

Page 1 of 10

If you are planning on using load sensors you will need to obtain or

purchase four units. We recommend our Combinator Board to make it easy

to turn the four strain gauges into a wheatstone bridge type load cell.

(Single strain gauge load cells only have three wires instead of four.)

Suggested Reading

If you aren’t familiar with the following concepts, we recommend reviewing

them before beginning to work with the HX711 Load Cell Amplifier Board.

• Load Cell Basics

• Getting Started with Load Cells

• Installing the Arduino IDE

• How to Power Your Project

• Battery Technologies

• How to Solder

Load Cell Set Up

A selection of different load cells

Depending on the type of load cell you are using, the configuration of how it

should be hooked up to plates or surfaces will change. Below are a few

different types of setups.

Load Cell - 10kg, Straight

Bar (TAL220

)



SEN-13329

Load Cell - 10kg, Wide Bar

(TAL201)

SEN-13330

1. [Strain gauges are two wired organized metal foil or wires that are set up in such a way that the resistance changes

when it is compressed or stretched. When a strain gauge is placed on something (usually metallic in nature) its

resistance changes based on the stress experienced by that something. When a single strain gauge is hooked up to a

metallic cell, we are calling that a load sensors, which have three output wires. Load cells usually has four strain gauges

hooked up in a wheatstone bridge formation, which have four output wires. For more information on load cells, strain

gauges, and wheatstone bridges see our tutorial.]↩

Page 2 of 10

Bar load cell between a two plate configuration

S load cell configuration

Possible four disc load cell configuration in something like a bathroom scale

Bar strain gauge based load cells

Usually with larger, non-push button bar load cells you will want to hook up

the load cell between two plates in a “Z” shape, with fitting screws and

spacers so that the strain can be correctly measured as shown below:

Page 3 of 10

Note that only one side of the load cell is screwed into each board. This

provides a moment of force, or torque, on the strain gauge rather than just

compression force, which is easier to measure and much more accurate.

For smaller, push-button or disc load cells, you will want to make sure to

screw in the disc to a bottom plate (or surface you are measuring force

against), and center the beam, plate, or whatever else you are wishing to

measure the force of onto the “button” on the top. Usually another plate with

a hole is used to make sure whatever you are measuring is hitting the same

spot on the load cell each time, but it is not necessary.

Make sure to read the datasheet for the load cell you are using and get the

correct screws to fit into it.

• Note: If you are hooking together four of the SparkFun Load Sensors

using the Combinator board, you should position the four load

sensors equidistant from each other, just like the bathroom scales

shown in this tutorial.

Load cell measurements can be off by +/- 5% due to a range of things

including temperature, creep, vibration, drift, and other electrical and

mechanical interferences. Before you install your scale, take a moment and

design your system to allow for easy calibration or be able to adjust the

code parameters to account for these variations.

Hardware Hookup

Page 4 of 10

The HX711 Load Cell Amplifier accepts five wires from the load cell. These

pins are labeled with colors; RED, BLK, WHT, GRN, and YLW. These

colors correspond to the conventional color coding of load cells, where red,

black, green and white wires come from the strain gauge on the load cell

and yellow is an optional ground wire that is not hooked up to the strain

gauge but is there to ground any small outside EMI (electromagnetic

interference). Sometimes instead of a yellow wire there is a larger black

wire, foil, or loose wires to shield the signal wires to lessen EMI.

Four strain gauges (SG1 through 4) hooked up in a wheatstone bridge

formation

Here we have a large black wire, some loose wires, and foil and loose wires

respectively as EMI buffers

In General, each load cell has four strain gauges that are hooked up in a

wheatstone bridge formation as shown above.

The four wires coming out from the wheatstone bridge on the load cell are

usually:

• Excitation+ (E+) or VCC is red

• Excitation- (E-) or ground is black.

• Output+ (O+), Signal+ (S+)+ or Amplifier+ (A+) is white

• O-, S-, or A- is green or blue

Page 5 of 10

Some load cells might have slight variations in color coding such as blue

instead of green or yellow instead of black or white if there are only four

wires (meaning no wire used as an EMI buffer). You might have to infer a

little from the colors that you have, but in general you will usually see these

colors.

If the readings from the HX711 are opposite of what you are expect

(for example the values decrease as you increase weight) simply

reverse the O+/O- wires.

Once the load cell is is hooked up to the amplifier, you can hook up VDD,

VCC, DAT, CLK, and GND to a microcontroller such as a RedBoard or

Arduino board.

Note VCC is the analog voltage to power the load cell. VDD is the digital

supply voltage used to set the logic level.

PRO TIP: In many cases, you can just short VCC and VDD together. If

your microcontroller uses 3.3V logic however, you'll want to connect

VCC to 5V and VDD to 3.3V.

Load cell wires hooked up to the HX711 Amplifier board

The example code has DAT and CLK hooked up to pin 3 and 2

respectively, but this is easily changed in the code. Any GPIO pin will work

for either. Then VCC and VDD just need to be hooked up to 2.7-5V and

GND to ground on your microcontroller.

Fritzing diagram of HX711 amplifier connected to a RedBoard

Now, if you would like to set up four single load sensors with our

combinator board and amplifier, connect the five pins labeled RED, BLK,

WHT, GRN, YLW to the matching pins on the HX711. Next, connect each

of the four load sensors to the following pins:

• Red →+

•Black→-

•White→C

Page 6 of 10

The combinator board also has room for an 8 pin RJ45 socket, which can

be used to connect your project via Ethernet cables for long distance

applications.

Another nice thing about our combinator board is that most home scales

use four single strain gauge load sensors, so this is a handy board for

hacking your own scales at home!

Hacked home scale’s four load sensors hooked up to our combinator board

Example of a single strain gauge, or load sensor. Here RED is the center

tap

For load sensors, there isn’t a set color coded standard. Comparing the

scale pictured above with the load sensor schematic, while the black wires

matched, the red and white wires were swapped. Also, only two of the four

sensors used a white wire for the ‘center tap’ of the load sensor, the other

two used green. I connected the black wires to “-”, the red to “+”, and the

white and green wires to “C”.

To determine how to hook up your single strain gauge load cells to the

combinator, measure the resistance between the three wires. You should

find a larger resistance (close to double) between a pair. In our example the

resistance between red and black was 1.6 kΩ, and the resistance between

white/green and red was 800 Ω. Therefore, the center tap to the strain

gauge is the white/green wire. The center tap or center pin of your strain

gauge connects to the “C” pin on the combinator. The larger resistance

wires (red and black in this example) connect to the “+” and “-” pins on the

combinator.

Page 7 of 10

The combinator board hooks up the four load sensors in such a way that

two resistors in the wheatstone bridge configuration are constant values

and the other two are variable in this way:

To hook up the combinator board to the HX711 match the RED, BLK, WHT,

and GRN pins

Once you have the combinator board successfully soldered to the twelve

wires, you can now connect it to the HX711 amplifier board via the 4

standard load cell wires. You can use short jumper wires or if your

electronics are a long distance away from your scale consider using an

RJ45 connector and an ethernet cable to connect the combinator to the

HX711 amplifier.

Arduino Code

Now that you have your load cell, amplifier, and microcontroller hooked up,

you can add your code and start calibrating your setup.

You can download the most up-to-date code and libraries from the link

below.

GITHUB REPOSITORY

If you have never worked with downloading Arduino libraries or need a

quick reminder you might want to take a look at our tutorial on Installing

Arduino Libraries.

Or you can easily get started and running with everything in Codebender!

The first thing you will want to work with is the calibration code:

“SparkFun_HX711_Calibration”:

Page 8 of 10





 

SparkFun_HX711_Calibration (https://codebender.cc/sketch:123175?

referrer=sarahalmutlaq) by sarahalmutlaq

(https://codebender.cc/user/sarahalmutlaq?referrer=sarahalmutlaq)

ÈClone & Edit

(/?

referrer=sarahalmutlaq)

3Download

(https://codebend

referrer=sarahalm

[Edit

Please select a board 

Example using the SparkFun HX711 breakout board with a sc

By: Nathan Seidle

SparkFun Electronics

Date: November 19th, 2014

License: This code is public domain but you buy me a beer

This is the calibration sketch. Use it to determine the c

outputs the zero_factor useful for projects that have a p

Setup your scale and start the sketch WITHOUT a weight on

Once readings are displayed place the weight on the scale

Press +/or a/z to adjust the calibration_factor until t

Use this calibration_factor on the example sketch

This example assumes pounds (lbs). If you prefer kilograms

calibration factor will be significantly different but it

Your calibration factor may be very positive or very nega

and the direction the sensors deflect from zero state

This example code uses bogde's excellent library: https:/

bogde's library is released under a GNU GENERAL PUBLIC LI

Arduino pin 2 > HX711 CLK

3 > DOUT

5V > VCC

GND > GND

Most any pin on the Arduino Uno will be compatible with D





 

To program your Arduino from your browser, please use

Google Chrome (http://www.google.com/chrome/)/Chromium

(version 41 and above on Linux) or Mozilla Firefox

(http://www.mozilla.org/en-US/firefox/) (32bit only on Windows).

Dismiss

Once you have calculated your calibration factor of your load cell set up,

you can move on to other code, such as the simple scale output example

code, “SparkFun_HX711_Example”:





 

SparkFun_HX711_Example (https://codebender.cc/sketch:122922?

referrer=sarahalmutlaq) by sarahalmutlaq

(https://codebender.cc/user/sarahalmutlaq?referrer=sarahalmutlaq)

ÈClone & Edit

(/?

referrer=sarahalmutlaq)

3Download

(https://codebend

referrer=sarahalm

[Edit

Please select a board 

Example using the SparkFun HX711 breakout board with a sc

By: Nathan Seidle

SparkFun Electronics

Date: November 19th, 2014

License: This code is public domain but you buy me a beer

This example demonstrates basic scale output. See the cal

specific load cell setup.

This example code uses bogde's excellent library: https:/

bogde's library is released under a GNU GENERAL PUBLIC LI

The HX711 does one thing well: read load cells. The break

based load cell which should allow a user to measure ever

Arduino pin 2 > HX711 CLK

3 > DAT

5V > VCC

GND > GND

The HX711 board can be powered from 2.7V to 5V so the Ard

#include "HX711.h"

#define calibration_factor 7050.0 //This value is obtaine

#define DOUT 3





 

To program your Arduino from your browser, please use

Google Chrome (http://www.google.com/chrome/)/Chromium

(version 41 and above on Linux) or Mozilla Firefox

(http://www.mozilla.org/en-US/firefox/) (32bit only on Windows).

Dismiss

Check out the other example code in the Github repo, or Codebender for

powering down the HX711 (github, codebender) and known zero startup

(github, codebender).

Page 9 of 10

Resources and Going Further

Want to know more? Check out this tutorial if you haven’t already:

Need even more? Check out this awesome article wheatstone bridges and

load cell types.

Getting Started with Load Cell

UNE 11, 201

tutorial defining what a load cell is and how to use one.

Page 10 of 10

201

https://learn.sparkfun.com/tutorials/loa

-cel

-amplifie

-hx711-

reakout-hooku

-guid

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