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Picture of Arduino Load Cell / Scale
From the minds at http://arduinotronics.blogspot.com/

My goal was to create a programmable scale for weighing objects, parts counting, even directing product flow on a conveyor system.

I needed a load cell, a Arduino, and an amplifier.

 
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Step 1: The Load Cell

Picture of The Load Cell
On this load cell (from a Accuteck  W-8260-86W Postal Scale) the 4 wires coming from the load cell are:

Red: Excitation +
White: Signal +
Green: Signal -
Black: Excitation -

This matches the GSE / NCI / Sensotec wiring scheme.

http://www.controlweigh.com/loadcell_colors.htm
I disconnected the 4 wires from the control board in the scale, so they would be available for the next step.

Step 2: The Amplifier

Picture of The Amplifier
To increase the output of the load cell so that the Arduino can read it on an analog input, we will need a INA125P amplifier and a 10 ohm resistor. Connect to the Arduino as indicated on the attached schematic.

Data Sheet: http://www.ti.com/lit/ds/symlink/ina125.pdf
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AnthonyT66 days ago

Hi, I have wired up the above several times to assure all pins were correct. I am viewing the display monitor and I find the numbers basically stay the same averaging between analogValue: 13.50 and 13.59. I do not see any changes when weight is applied.without anything on pin one, numbers fluctuate between 18-20. Any ideas why I am not see a change or is it always that little?

sspence (author)  AnthonyT66 days ago
do a serial print of your analogRead, see what the adc is seeing. what value resistor did you add to the amplifier?

I am using same 10 ohms. Found E- and E+ were backwards. Now I get 5v out from analog pin not connected to Arduino. When connected to Arduino, I get: 25

analogValue: 870.01

load: 43.50033

analogValue: 870.01

load: 43.50046

analogValue: 870.02

load: 43.50091

I have not set anything, setup just as shown. I just want to make sure my setup is correct.

sspence (author)  AnthonyT66 days ago

IIRC, You will get 5v (1023 adc) at no load, and decreasing voltage with increased load.

Ok, so with analog pin not connected to the Arduino, I should see the voltage drop as I apply weight to load sensors, right? Yea. I don't see any changes. I guess the load cells I got from an old working digital scale don't work.

sspence (author)  AnthonyT66 days ago

Could be an issue with your amplifier chip as well. or a wiring issue. I have no way to tell from here. want to send a picture? greentrust@gmail.com

I am using jumpers on a bread board. You know how messy that can look. Three more questions:

1. The code states using two weights. I am looking to eventually do something when weight exceeds 50 lbs, perhaps trigger a relay, alarm, etc. How far apart in the two weights would be sufficient for a good calibration?

2. How is a minimum and maximum value set? For instance, 5v is 1024 correct? If I wanted 50lbs to be maximum value, what do I need to do?

2. Where can I find code that will not produce a continuous serial output if there is no weight on the load cells? Serial is continuous, whether the value is the same or not.

If I haven't thanked you yet, THANKS!!!

sspence (author)  AnthonyT65 days ago

the larger the difference in weights, the better the calibration I would think. The maximum is the the value in the data sheet for your scale. What ever it's capable of measuring. If it's a 150 lb scale, it will output 0v at 150 lbs, and 5v at zero lbs. You can code your sketch to only do a serial print if the scale reads not equal to zero.

if (weight!=0){

Serial.print(weight);

}

With a LCD output, you want to display continuously.

can you email me the calibration code?? i cant actually see the code for calibration? can you atleast guide me????

@taherdalroti : I guess sspence refers to the original Calibration code you can find in the Arduino IDE software.

sspence (author)  suddenci15 days ago
No, the calibration is what is displayed when you put the two weights on the scale. read the code. it's documented.

Hi! I would just like to ask if increasing the resistor from 10 ohms to 1k ohms make any difference? And what is the purpose of the resistor anyway?

sspence (author)  sarcasmoverthetop15 days ago
Makes a lot of difference. It sets the amount of amplification. Read the data sheet on the instrumentation amplifier.
AnthonyT61 month ago

Hi, Where is the output displayed when you add weight to weigh?

sspence (author)  AnthonyT615 days ago
Serial Monitor. You can add a lcd or other type of display if you wish.

Hello,

My need is similar to to the previous inquiry, my need is for two small load cells.

Looking on ebay, I see cells with only 3 wires. Can this be done, and could I bother you for a quick sketch showing how to hook them up? Thanks in advance.

Small cell.JPG

@Steve.muscato.1 : the load cell you showed is an half wheatstone bridge. Hence you have to use two of them to get a complete bridge :-)

contact mee... dilupajayanatha@gmail.com

sspence (author)  steve.muscato.18 months ago
This may help you! - http://electronics.stackexchange.com/questions/18669/how-to-wire-up-a-3-wire-load-cell-strain-gauge-and-an-amplifier

I think I am beginning to understand.........these are 1/2 bridges. Still could use help hooking them up.

Joseph AlvinS2 months ago

What could replace the INA125?

sspence (author)  Joseph AlvinS2 months ago
Pretty much any single supply instrumentation amplifier - http://en.wikipedia.org/wiki/Instrumentation_amplifier
kamalkannan122 months ago

Can I make amplifier circuit with INA126P?

pascalBOP2 months ago
(removed by author or community request)
sspence (author)  pascalBOP2 months ago
says what?
pascalBOP sspence2 months ago

I wrote you an email at sspence@green-trust.org

Hello sspence, nice post of your project.

can you help me to describe schematic of load cell 200kg with wires :

Black Power + ,

white Power – ,

Red Signal + ,

green signal –?

thanks a lot of..

permisi kak, mau tanya dong, kakak make load cell 200kg? kebetulan saya sedang menyusun tugas akhir, dan akan menggunakan load cell kira2 100 kg atau 200 kg. saya bingung nyari load cell 200 kg secara online.

sspence (author)  rinanda.febriani3 months ago
http://www.controlweigh.com/loadcell_colors.htm
widpyro3 months ago

can you please post code for controlling switches at different load values.

thanks,

-jim

adsmith064 months ago

Hello,

I am using your directions to help me with a school project and I was hoping there are alternatives to buying the INA125P amp online. Sellers of this item are shipping internationally and I am afraid that it would take weeks to get to me.

sspence (author)  adsmith064 months ago
Where are you located? Digikey, mouser, newark and allied all carry this, AFAIK.
noel.keen6 months ago

Very cool and almost exactly what I am looking for.

Question: Is there a reason to disconnect the wires from load cell to the board on the scale? Couldn't you have tapped into the existing connections and run the scale and arduino in parallel? That way you could see the scale weight and also use the arduino. I'm asking because this would be ideal for my need.

beta943058 months ago

Hi! I am hoping to connect a digital bathroom scale (similar to this, but has 4 strain gauges at each corner instead of one load cell) to an arduino and be able to read out the input. Do you have any advice?

sspence (author)  beta943058 months ago
read all 4, add the results together.
Godfather1310 months ago

Small question: what sofware do you use to draw the circuit? Thanks a lots :)

sspence (author)  Godfather1310 months ago
http://www.digikey.com/schemeit

thank you :)

nimble991 year ago

Can I swap the INA125P for an INA125PA? Looking at the spec sheet, I'm guessing that the PA is just a more tolerant part?

talsayed1 year ago

hi guys,

I really need your help,

Actually, I'm working on a senior design project, which is building a Tractor. I will be working on the electrical connections + the micro controller ( Adruino Uno). My electrical connections will contain the following :

- Battery 12Vdc. will be hooked up to the Adruino and transformer. I hooked it up with a transformer in order to amplify the voltage between 18 - 24 voltage to feed the load cell. I'm going to use 2 quantity of Load cell ( For you record). And Then from the load cell to Microcontroller ( Adruino Uno).

hers is the type of the load cell that i'm going to use.
http://www.interfaceforce.com/index.php?1200-Preci...

The question is: should i hook the load cell with signal conditioner first? if yes, HOW ??? despite i'm going to use TWO of Load cell?

here is the signal conditioner that found ???
http://www.interfaceforce.com/index.php?1200-Preci...

which is the fourth file from the bottom of the list.

anyone can help me with the connection ????????????

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