Interfacing a Load Cell With an Arduino Board | RobotShop Community

pvfranco97 · July 16, 2019, 10:14pm

Thank you for the quick response! That worked perfectly.

One more question, I am trying to connect a half-bridge strain gauge to the shield, but I am not sure which pins to connect it to. Could you help me with it? Thanks again.

Pablo

pvfranco97 · July 18, 2019, 6:04pm

hello,

I am trying to connect the shield to a quarter bridge strain gauge but when I apply the voltage, the current is too high (and has burned the arduino). I checked the wiring a few times and I think it is properly set (with 3 dummy resistances and the load resistance). Is there something I may be missing?

bdaouas · July 22, 2019, 1:40pm

What is the resistance values of the resistors and the strain gauge ?
How was your bridge powered ?
Could you provide a wiring diagram of your bridge ?

pvfranco97 · July 23, 2019, 7:44pm

I tried two different setups (shown in the pictures); the strain gauges have a nominal value of 1k.
I think there was a mismatch between the shield datasheet and the webpage of strain gauges configuration given at the site. I checked with different tests and got it to kinda work.
Now, I can get the shield to output either 0V, 3V, or somewhere approximately in the middle (i.e. 1.4 V) but it does not show the change in voltage.
I tried using another amplifier box and I did get a signal but with the shield I am not getting any feedback signal (not even a small one).

SG wire setup.pdf (621.0 KB)

bdaouas · July 24, 2019, 12:08pm

The gain of the AD8426 instrumentation amplifier IC is set to 495 by default on the shield with the gain resistor Rgain = 100 Ohms. A voltage input from the wheatstone bridge of 1.4V or 3V will saturate the output of the amplifier. You probably need to remove the gain resistor for your application (Gain 1 or Gain 2 depending on the channel you are using). When no gain resistor is used, the gain of the AD8426 would be 1 and gain error and drift are minimal. Please note that the gain resistors are smd components, therefor, some smd soldering skills might be needed.

MartinM · August 27, 2019, 11:31am

Hello, everybody,

I have been working on a load readout device using load cell 0-300kg with an excitation of 10V and an output of 2mV/V. I have searched the internet and have found 2 ways of doing it first with HX711 amplifier second with load cell shield or nanoshield (company from Brazil make them). Do you know what would be the difference between them two? Which one give me more stable more accurate readout?
Thanks

bdaouas · August 28, 2019, 1:24pm

Hi,

The HX711 Load Cell Amplifier is a single channel amplifier with a digital interface output and provides a 24 bit resolution which is higher than the Arduino’s 12 bit. However, the data output rate only goes to a maximum of 80Hz. The Load Cell / Wheatstone Amplifier Shield is a 2 channel analog output amplifier with a default of 100Hz filter (that can be removed for faster data output rate), therefore, it would be only limited by the ADC sampling rate of the Arduino board that can theoretically be 9600Hz. Also, it’s important to note that the Shield allow a maximum excitation voltage of 5V.

Giannis_D · February 23, 2020, 12:50pm

Hello,

I ve read that the shield has two channel so that 2 load cells can be used. I would like to ask :

Is it possible to get measurements for these 2 channels simultaneously in real time applications?
Are the gains of each channel independent of each other?
Is this shield possible to be mounted in NUCLEO-F334R8 microcontroller and in which way ?
https://www.st.com/en/evaluation-tools/nucleo-f334r8.html
(It is a ST microcontroller with both Arduino uno v3 connectors and ST connectors)

Thanks
Giannis

bdaouas · February 24, 2020, 2:37pm

Hi,

The Load Cell / Wheatstone Amplifier Shield (2ch) provides 2x independent load cell analog outputs, therefore, yes you can get measurements for these 2 channels simultaneously.
Yes the gains for the 2 channels are independent of each other. Each channel has a gain resistor (Gain1/Gain2) that can be changed.
The Load Cell shield has an Arduino UNO shield form factor. It will provide the analog reading of channel 1 on the analog pin A0 and the analog reading of channel 2 on the analog pin A1. It should work with the NUCLEO-F334R8.

Hope this helps,

Giannis_D · February 24, 2020, 5:12pm

Thanks for the quick and useful response.

I would like also to ask:

Let’ s say that I am using only channel 1. What does the pin A0 give me as reading, if I do not use the library code, but just analogRead(A0) ?
For what I can understand it will be an integer (let’s say n ) between 0 and 1023, right ?
If yes, I can convert my reading to Volts with the formula : Vout = n*4.9 mV , right?
I ask because I do not want to print the reading in kg or lbs, but in Volts.
From what I understand, the shield will work for a Wheatstone half bridge (not a load cell but other application) with 350 Ohm gages and resistanses, right?
Best wishes
Giannis

bdaouas · February 25, 2020, 2:28pm

Yes and no : If you had an Arduino UNO Board (10-bit ADC with 5V default reference voltage) that would be correct. However, the NUCLEO-F334R8, you are planning to use, has more ADC resolution than an Arduino UNO (12-bit ADC). Therefore, if the NUCLEO-F334R8 has a 5V ADC reference voltage, the formula would be Vout = n*1.22mV
It’s actually the other way around, the shield can directly work with load cells. You can connect a full bridge load cell to each channel and get independent readings on A0 and A1.

Giannis_D · February 25, 2020, 3:19pm

Ok, I maybe wasn’t clear about my second question.

I know that this shield is designed for full bridge load cells . However, my application is a half bridge strain gage application in a component beam that gets bending (and not an already integrated load cell). So, I am gonna do the strain gage installation and wheatstone bridge on my own in my own specific beam. What I am asking is if the shield will work with such a half wheatstone bridge comprised of 350 Ohm strain gages and resistors ?

Thanks for the help,
Giannis

bdaouas · February 26, 2020, 2:58pm

The shield is based on the AD8426 Instrumentation Amplifier which should normally work with all configurations of wheatstone bridge measurements (quarter, half, full). Therefore, it should work with your half bridge setup although we didn’t test it, some of our customers have used it to get half bridges readings and it worked without issues.

Giannis_D · March 4, 2020, 6:37pm

Hello bdaouas,

According to my application I described earlier which is half bridge. Is the shield capable of reading strains in two different directions of the force applied?
For further explanation see the picture below :
Is it distinguishable when bending is “positive” (R1 stretched and R2 compressed) with the case when bending is “negative” (R2 stretched and R1 compressed) ?
From what I understand reading must have different sign, right ?

bdaouas · March 6, 2020, 9:24pm

This has been replied here

mist_hellfire · October 7, 2022, 5:01pm

@bdaouas A few questions:

Can this be used as a single channel for a single loadcell?
How is the filter removed to increase above 100Hz and specify a Hz?
Thanks in advance.

cbenson · October 11, 2022, 5:39pm

@mist_hellfire Welcome to the RobotShop Community. Assuming you are referring to the product below, it’s effectively a breakout board for the AD8426 amplifier module:

Datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/ad8426.pdf

Yes, you don’t need to use both channels and can use just one.
As for the filter, do you mean what’s referred to on page 24 of the guide above?