2011

Author: Manoj

Reviewer: Ram

Revision: 1.1

Tenet Technetronics

6/20/2011

Application Note: AN100 Load cell breakout user manual

i

Contents

Introduction

Introduction to Loadcell breakout

Hardware Overview

Loadcell breakout features

Schematic

Software Overview

Flow Chart

Pseudo code

Code

Demo Application

References and further reading

1

Introduction

Loadcell breakout allows an Arduino/Comet board to connect to the loadcell. It is

based on the INA125P instrumentation amplifier from Texas instruments. This breakout board

is intended to make the interface between the Arduino and an instrumentation amplifier easier

thereby allowing various measuring devices like a loadcell to be connected.

The breakout also provides an easy way to connect a 16x2 LCD as well as a potentiometer to

vary the gain value of the on board amplifier.

Note: A loadcell is an energy conversion device. The conversion can be to/from electrical,

electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. Here

it is used to convert a force into electrical signal. The mechanical arrangement is done with

loadcell on which a load is applied and the force applied is converted electrically and the output

signal is amplified by an instrumentation amplifier INA125P (Texas instruments) before it can

be used.

Loadcells are used in several types of measuring instruments includes electronic weighbridge

force measurement, portable weigh scales etc.

2

Hardware Overview

Figure1: The loadcell breakout shield

Loadcell breakout features

Compatible shield for Arduino/comet.

Breakout comes with 16x2 LCD.

Uses INA125P instrumentation amplifier.

Adjustable gain.

3

Components overview

Table1: components overview

Components

Brief

specification

Product link

References

INA125P

instrumentation

amplifier

Single

Supply:

2.7V to 36V

Dual

Supply:

±1.35V to

±18V

http://tenettech.com/

product.php?id_prod

uct=1500

http://www.datasheetcatalog.org/datasheet

2/9/0pap54gi53u7p7a57xjpzfs0tcky.pdf

Gain adjustable

potentiometer

Resistance:

10 kilo ohm

http://tenettech.com/

product.php?id_prod

uct=1498

http://en.wikipedia.org/wiki/Potentiometer

Reset button Normal push

button

http://tenettech.com/

product.php?id_prod

uct=1499

http://en.wikipedia.org/wiki/Push-button

Extended LCD

berg

connectors

16x2 LCD http://tenettech.com/

product.php?id_prod

uct=517

http://en.wikipedia.org/wiki/Liquid_crysta

l_display

4

Schematic

Gain of the INA125 is set by connecting a single external resistor, (RG)

between pins 8 & 9.

3,5,13 pins of INA125 & 8th

pin of ATMEGA328 – Ground.

1, 2 pins of INA125 & 7th

pin of ATMEGA328 – Vcc.

23rd

pin of ATMEGA328 (analog pin) to 11th

and 12th

pin of INA125.

4th

and 15th

pin of INA125 is shorted.

Figure 2: loadcell breakout schematic

Note: the loadcell wire color coding

Figure 3: color code of load cell wire

5

Software overview

Flowchart

Initialization of LCD,

reference load A and B

Print the values

Read the Analog

values and average

Map the outputted

floating values from

reference loads(A & B)

Start

End

6

Pseudo code

Include header files for LCD

Global declaration:

For two different loads (in example load A & B).

For Analog values for loads and average analog value.

For time between readings.

Function name : setup

Return type : void

Description : serial communication initialization.

LCD initialization.

Function name : loop

Return type : void

Description : read the Analog values.

Running average for smoothening.

Call for mapping function.

Print the values.

7

code

// Load cells are linear. So once you have established two data pairs, you can interpolate the

rest.

// You need two loads of well know weight. In this example A = 0 kg. B =64 kg

// Put on load A

// read the analog value showing (this is analog val A)

// put on load B

// read the analog value B

#include <LiquidCrystal.h> //we need this library for the LCD commands

LiquidCrystal lcd(12, 11, 10, 5, 4, 3, 2); // initialize the library with the numbers of the

interface pins

// Enter your own analog values (without load) here

float loadA = 0; // kg

int analogvalA = 15; // analog reading taken with load A on the load cell

float loadB = 64; // kg

int analogvalB = 143; // analog reading taken with load B on the load cell

// Upload the sketch again, and confirm, that the kilo-reading from the serial output now is

correct, using your known loads

float analogValueAverage = 0;

long time = 0; //

int timeBetweenReadings = 1000; // We want a reading every 1000 ms;

void setup() {

pinMode(13, OUTPUT);

digitalWrite(13, HIGH);

Serial.begin(9600);

lcd.begin(16, 2); // tells Arduino the LCD dimensions

lcd.clear(); // clear LCD screen

lcd.setCursor(0,0);// set the cursor

8

void loop() {

int analogValue = analogRead(0);

// running average – We smooth the readings a little bit

analogValueAverage = 0.99*analogValueAverage + 0.01*analogValue;

// call the arduino MAP function

float load = analogToLoad(analogValueAverage);

if(millis() > time + timeBetweenReadings){

lcd.clear();

lcd.print(“Weight = “);

lcd.print(load,2);

time = millis();

}

}

float analogToLoad(float analogval)

{

// using a custom map-function, because the standard arduino map function only uses int

float load = mapfloat(analogval, analogvalA, analogvalB, loadA, loadB);

return load;

}

float mapfloat(float x, float in_min, float in_max, float out_min, float out_max)

{

return (x – in_min) * (out_max – out_min) / (in_max – in_min) + out_min;

}

9

Demo Application

This demo shows the Comet interacting with INA125p instrumentation amplifier to measure the

load applied on the loadcell

Figure 4: loadcell breakout

Loadcell breakout is mounted on the Comet board and LCD is connected to loadcell breakout

through the extended berg connectors

Figure 5: breakout with Comet board Figure 6: breakout with Comet board and LCD

10

The loadcell sensor with metal gauge on which the load is applied is connected to the breakout board

Figure 7: loadcell sensor with metal guage

The Arduino code for loadcell is written and uploaded to Comet board

Figure 8: Arduino sketch

The output result displays the weight applied on the load cell

Figure 9: results displayed on LCD

11

References and Further Reading

http://www.datasheetcatalog.org/datasheet2/9/0pap54gi53u7p7a57xjpzfs0tcky.pdf

http://tenettech.com/search.php?orderby=position&orderway=desc&search_quer

y=loadcell&submit_search=Search\

http://en.wikipedia.org/wiki/Load_cell.

www.arduino.cc

www.tenettech.com/comet