Instructables
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
adsmith066 days 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)  adsmith066 days ago
Where are you located? Digikey, mouser, newark and allied all carry this, AFAIK.
noel.keen1 month 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.

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
sspence (author)  steve.muscato.13 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.

beta943053 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)  beta943053 months ago
read all 4, add the results together.
Godfather135 months ago

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

sspence (author)  Godfather135 months ago
http://www.digikey.com/schemeit

thank you :)

nimble999 months 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?

talsayed10 months 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 ????????????

sspence (author)  talsayed10 months ago
Transformers only work on ac, not dc. If you feed the load cell at higher than 5v, you will damage the amplifier chip and or the arduino. They only take 5v inputs. You could drop the output voltage with a voltage divider, but that cell does not need a high voltage input. It's rated for 20v MAXIMUM, but should work fine on a lower voltage.
steam22811 months ago
Hello, I really need some help around this!
I'm using this cell: http://www.phidgets.com/products.php?category=34&product_id=3135_0
and trying to hook it to an arduino with this circuitry....
The thing is that the only reactions I get in the analog value...besides some 11,90 something to 13,00 something variation it really changes when my hand is near the green cable.....
I reassembled everything 10 times, changed the ina125 and really can't find the problem!
Thanks in advance,

André
sspence (author)  steam22811 months ago
you might want to adjust the calibration resistor without the arduino connected. you should see 5v with no weight on the scale, and the voltage decreases with additional weight. you will need to calibrate the scale as specified in the code.
steam228 sspence11 months ago
Thank you very much,

sorry, what do you mean by "adjust the calibration resistor without the arduino connected"?

I want to calibrate it, but that doesn't influence the analog value, right? I cannot start that calibration if I don't stabilize the analog value signal?

Thanks again
baring1 year ago
Hy Sspence,

Congratulations for your project and thanks for sharing it and being suportive with our questions.

I'm also working with load cell and arduino but i'm struggling to get the precision you mentioned on a friend comment. (0.01g 36kg).

I'm using a 30 kilos load cell and minimum value I read is 0.30g. And it increases in 0.30 like - 0.30g, 0.60g, 0.90g...30 kilos.

How can I get a 0.01 precision?

Thanks for the answer!
sspence (author)  baring1 year ago
precision has to do with the mv per step, and the output of your load cell / amplifier. It also has to do with the data type you use. A float should be sufficient for your application. 5v / 1024 = .0048 mv steps,
arvinsj1 year ago
Yep. The fluctuations happen with no load changes.

I thought it might be a loose wire as well. I re-did all the connections. The connections are fine now.

But the problem still exists.

Is there something else I should be looking out for? I have been breaking my head trying to think of other reasons.
sspence (author)  arvinsj1 year ago
Maybe the INA125 went bad? They are susceptible to ESD.
arvinsj1 year ago
Hey,

I have been working on this load cell project.

Things were going alright.

Now out of the blue the analog readings from the weighing scale are going haywire.
A lot of fluctuations.

Do you have idea why this is happening?

Is it some kind of wear and tear problem?
sspence (author)  arvinsj1 year ago
Sounds like a loose wire. Are the readings fluctuating with no load changes? There are no wear and tear issues, these load cells work for years.
madtrick1 year ago
For the load cell you were using, what was the excitation voltage? I'm viewing some load cells with 10v input and was wondering whether yours is too, but works fine with 5v?
sspence (author)  madtrick1 year ago
It doesn't matter, it's a voltage divider. I'm using 5v.
espdp21 year ago
As an Arduino white belt, I'd like to say this is cool. I didn't get why you would want to do this at first, but I think I can see good uses for it now, after re-reading it. I'd like to know, after calibration, how sensitive is it, and *roughly* what are the minimum and maximum weights that you can practically measure?
sspence (author)  espdp21 year ago
Precision, min & max all depend on what load cell you use and whether you are in kg or lbs. I'm only looking x.xx in grams for the most part, and with this unit I can measure as little as .01g up to 36,000g or so.
sspence (author)  sspence1 year ago
From http://arduino.cc/en/Reference/AnalogRead:

This yields a resolution between readings of: 5 volts / 1024 units or, .0049 volts (4.9 mV) per unit.

So that's your resolution limit.