I see here that "Pin 15 and 4 aren’t connected for a start, and there were a few other tweaks to make"
But as far as I see in your fritzing picture you connect pin 4 to 16 .
Again I think I miss something, specially about "other tweaks to make".
I am planning build a test circuit using +12v/-12v from pc power supply and see the results.

 

hi,
I have been checking the INA125 and without a -12V supply you will not get a Vout=0v for 0mVin.
Also with a single supply +12V, you must have an Aref [pin #5] with at least +2.5V, this will of course mean Vout=2.5V for 0mVin.

As you are planning to use +12v/-12V supplies, the INA125 should work as expected, with Aref =0mVin and Vout=0 for Vin =0v

E

Update: Connecting pin 4 to 16 enables +10Vext for the bridge [ if you are not using a current boost transistor]

 

Hi again.
I did another test pcb using this schematic (ina-new.jpg). I powered it from a pc power supply like previous but now used -12V rail also. I grounded load cell shield and also added transistor like in picture. I also used 1k resistor for the gain.

These are results I get (All results are in mV)
0kg - 6
50kg - 31.6
100kg - 70.3
150kg - 108.6
200kg - 147
250kg - 185.3
300kg - 223
350kg - 261
400kg - 299
450kg - 337
500kg - 375
600kg - 452

Because the loads was not exactly precise (eg: cannot turn exactly to push 400kg and get 399 - 401) I think they look good.
I will do a proper measurement probably tomorrow, when I will borrow a precise calibration tool for gauges.
I also turned back to 0 through almost same loads and get almost same values.

Question : in my schematic I have there also a 10uF polarized capacitor which I haven t put now because didn't found one..is that necessary ? Should I use it in final pcb?

Thank you again for all your support.

btw - if there is any interest I can post here (after finish) all project including (ina226 and arduino readings )

 

hi David,
Pleased that you have made progress, we will be interested in seeing your project, it may help others.

I would add the 10uF decoupling cap on the supply.

E
EDIT:
Plot of your test results.

 

Thank you.
Now I am thinking to find a way to power up the project (all 6 ina125) because I see the PC power supply can only deliver 0.5A on -12V rail...
Thanks again

 

Thank you.
Now I am thinking to find a way to power up the project (all 6 ina125) because I see the PC power supply can only deliver 0.5A on -12V rail...
Thanks again

hi,
Check the d/s for the very small negative current required by the INA125, a 0.5A -12Vdc source should have no problems.
E

 

I have built several INA125 amps for load cells using both single and dual supplies. A single supply is viable but will have an appx 150 mv offset which can be zeroed out using either additional circuitry or software depending on the application. For dual supply operation I used a TL7660 converter chip to provide the negative supply which only needs to be a few volts.
SG

 

So there is no need of -12V ? Can I use that TL7660 powered from my 12V power supply?
Also, should I put 1 TL7660 for each INA I use?
Do you have an working schematic of this?
Thanks a lot

 

An ordinary TL7660 from Texas Instruments goes to a maximum of 10 Volt supply.

With a +5 Volt supply and 5 mAmp consumption there should be -4.5 Volts on the output.

 

And is ok if I feed INA with +12V / -4.5V ?

 

hi D,
These are one option, choose an isolated version 12V to 12V. [ or lower if you prefer]
IE

 

Couple of variations I have used.
SG

 

So basically in your dual supply you feed ina with +12V / -5V. Is that right? If so, I think this is fit for my needs

Q2 - Do I have use one TL7660 for each INA or can use one for few INA ?
Thank you

 

Correct, drive the TL7660 with the 5 volt reference voltage.
One TL7660 should be able drive several if not all six circuits you have in mind.
SG

 

Thank you again for all help
I will get back when finish the project (if not other issues ) and will post it complete here
Thanks