Hello,
Please, what do you think about the amplifier circuit below?
It is a battery powered load cell meter.
More force on R1 causes more resistance.
The U1 should be changed to AD623 that has Rail-Rail output.
The target resolution should be about 0.1% of max. value.
The MCU will have TARA button to set zero value.
www.ti.com/lit/ds/symlink/ina126.pdf
www.ti.com/lit/gpn/lm185-1.2-n
http://www.analog.com/static/imported-files/data_sheets/AD623.pdf

 

I have just found this threat:
http://forum.allaboutcircuits.com/threads/load-cell-amplification-ina125-problems.102777/
There is nice workaround for limited output swing of IA. Thank you !!!

 

Hello,
Please, what do you think about the amplifier circuit below?
It is a battery powered load cell meter.
More force on R1 causes more resistance.
The U1 should be changed to AD623 that has Rail-Rail output.
The target resolution should be about 0.1% of max. value.
The MCU will have TARA button to set zero value.

www.ti.com/lit/ds/symlink/ina126.pdf
www.ti.com/lit/gpn/lm185-1.2-n
http://www.analog.com/static/imported-files/data_sheets/AD623.pdfView attachment 77776

You could replace R3 with a 200 ohm variable resistor (multi-turn potentiomter) plus a 910 ohm fixed resistor to balance your bridge.

 

Hello,
I tried to build it. I used R9,and R10 instead of the real load cell, R1 is 1k
I didn't have MCP6002 on my hand, instead, I used MCP602 as IC1 (it doesn't have R2R input).
Then I checked the output with an 12bit. ADC@Vref=3.3V/ uart converter.
It seems that the outputs measured values have picked up a noise...

 

You might want to try adding a capacitor across your LM385 reference. Also, add external resistors as needed to bump your reference to 1/2 of supply voltage instead of 1.2 v.

If that is not enough, add another resistor between neg supply rail and your inAmp ref input.

 

Šťastný nový rok!

Why R20?
Why is IC1A needed?
Why is IC1B needed?
Where is the anti-alias filtering?

 

Thank you for replies very much!
I thought IC1B would make calculation (y=1.5*x-0.5*vref) to 'extend' the IA output range {0.7V..2.3V}. But now it seems it is not so important.
I will remove IC1A, IC1B and I try again...
There is also similiar application note in TI DS INA126.

Edit1: the results are much better with the anti-aliasing filter. Even when tested on DIY board...

 

Hallo,
please I would have one more question regarding the balancing input bridge.

 

Hallo analog experts,
I had a chance to make an update. Please what you think about the schematic?
I would like to know your opinion. I didn't design such complicated thing so far.
The result seems good. 'Green' is the value as a number after ADC conversion (0..3V)->(0..4095).
'Red' is LM385 reference. The MCU makes simple calculation n=(n1+n2+..+n8)/8.
The 'm1' pictures are for IC1A:Vout=~2.5V.
The 'm2' pictures are for IC1A:Vout=~0.6V.