Which amplifier to get when interfacing load cells with an Arduino

Thread Starter

verynewtothis

Joined Apr 19, 2019
9
I'm quite new to this, so I'll explain as much as I can.
I need to interface x4 3-axis load cells with an Arduino Mega, and I know I need an (operational?) amplifier to boost the signal, however, I do not know which amplifiers I should get, where to get them, or which parameters to even look for.

Here is all the information I could get regarding the load cells:
If it helps I will only need the X and Z axes.
Range: Fz=5KN, Fx=2KN, Fy=2KN
Output: 2mV/V Fx/Fy, 0.33mV/V Fz
Capture.PNG
 

Thread Starter

verynewtothis

Joined Apr 19, 2019
9
hi v,
Welcome to AAC.
Have you considered the HX711 load cell amplifier, it has lots of Arduino information on the web.
E
I have seen these, but I was under the impression that they only work with certain load cells (https://www.sparkfun.com/products/14729) as they boost the voltage to the correct amount for the Arduino.
As my load cells are different and output a different voltage, wouldn't the same amplifier get it to an incorrect level? I might be wrong, in which case does this mean I can put the HX711 in front of any load cell and it would work?
 

ericgibbs

Joined Jan 29, 2010
14,114
hi V,
Do you have a picture of one those loads cells.?
If you want to power the load cells and Amplifier with say 10V , look at the AD630 IA [ instrumentation amp]
We can then help with the design.
E
 

Attachments

ericgibbs

Joined Jan 29, 2010
14,114
hi v,
Thanks,
Your original data table shows 10V excitation.
How many wires come out from the sensor, and do you know how they are coded.?
E

AA3 19-Apr-19 13.59.gif
 

ericgibbs

Joined Jan 29, 2010
14,114
There are 4 wires for each axis, and I think they are something like E+, E-, A-, A+.
hi,
E+ and E- are excitation.
The A's are the millivolt output signals.
Can you confirm that you intend using 5Vext.?

I believe your original values are for 10Vext, halving the Vext will halve the output to 1mV/V

Range: Fz=5KN, Fx=2KN, Fy=2KN
Output: 2mV/V Fx/Fy, 0.33mV/V Fz
 

ericgibbs

Joined Jan 29, 2010
14,114
The Arduino takes between 0 - 5V, so I guess 5V.
So for 5Vext at 1mV/V that is a maximum of 5mV, so for 5V into the ADC thats 5V/0.005V = Gain of 1000.

For that level of gain the AD623 would say amplify by 100 and a second regular OPA with a gain of 10 would raise it to 5V.
This means the 2nd OPA would have to be a rail to rail OPA, a MCP6002 for example.

Do you follow that OK.?
E
 

ericgibbs

Joined Jan 29, 2010
14,114
Hi v,
Woops!

The load cell datasheet says Vext =10Vdc, which will output 2mV/Vext, full load =20mV.
Driving the load cell at half the rated voltage ie: 5Vext will give only 2mV/Vext, full load = 10mV.

Set the gain of the AD623 to 50 [ not 100] keep the MCP gain at 10
So thats 10mV * 50 = 0.5V , then times 10 = 5Vmax.

E

EDIT:
Corrected my error . :oops:
 
Top