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ADS1232 lecture keeps decreasing

Daniel Rodriguez1
Prodigy 35 points
Other Parts Discussed in Thread: ADS1232

Hi everyone!

I'll try to explain my problem, I already read the post that the the title box suggested me, but I could not find something to help me.

Maybe something about the offset.

What do I have

So I have a ADS1232 which seems to work pretty good, the sensibility is just great.

To the ADS1232 I have connected 2 load sensors (3 wires each) and all the connections as specified in the data sheet 

http://www.ti.com/lit/ds/symlink/ads1232.pdf   Page 25, Figure 42

The main differences are that: I'm not using an external crystal and the micro controller is 32bit ARM .

The experiment

So on experimentation I found that I can read the differences of Kilograms, even half Kilograms ( I'm from Chile, here we use Kilograms instead of pounds).

That numbers in the reading is 22.000, so If I apply 1 Kilogram on the base (where the sensor are) the sensor lecture rises 22.000 which works pretty well. Tried with 1, 2 ,3 , 1 1/2  to 70 Kilograms and seems to be correct.

The Problem :(

The problem is that the lectures of the sensor keeps decreasing, for example if the ADS1232 sends 688.974 on the beginning it keeps falling to 480.000 and then increase again and the decrease again. If I apply a Kilogram to the sensor it will rise that value adding 22.000 to it.. however it start to fall again. and keep dancing.

It seems I'm not able to have a steady basal measure.

What have I tried 

So far I tried by building everything up again, double check the sensor, the connections, the caps, even the code. But it seems I'm missing something.

I've also found that the +5V power supply seems to oscillate due the ADS1232.

So please if anyone had a problem like this and have a suggestion, or a TI user may have a solution, please let me know.

Thanks in advance!

  • 0
    TI__Guru** 113765 points

    Hi Daniel,

    Welcome to the forum! It appears that your system is not stable.  Are you using a prototyping system to build your circuit?  This often will have problems with noise and oscillation.  To get high levels of precision requires high grade components and a PCB with a good ground plane.

    Can you send me your specific schematic and any information on how you are connecting the components?

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 35 points

    Bob Benjamin said:

    Hi Daniel,

    Welcome to the forum! It appears that your system is not stable.  Are you using a prototyping system to build your circuit?  This often will have problems with noise and oscillation.  To get high levels of precision requires high grade components and a PCB with a good ground plane.

    Can you send me your specific schematic and any information on how you are connecting the components?

    Best regards,

    Bob B

    Hi Bob B!

    Thanks mate!

    Indeed, it seems it was completely my fault, on my design I have a wireless device may be to near, so I deactivate it while doing the readings, and add a few caps to stabilise the VDD and AVDD.

    It seems is very sensible to any noise and emf. However works amazing!

    I reckon it would be a good idea to isolate as much as possible the ADS1232 on the PCB designs.

    Cheers!

  • 0 in reply to Daniel Rodriguez1
    Prodigy 170 points
    Hi Daniel,
    I'm working on Ads1232 ref board ,after following all the steps mentioned in the user guide I'm facing the same problem that you have mentioned i.e., the weight value of an object that is getting displayed is not stable its either continuously increasing or decreasing , can you please suggest me the steps you followed. to rectify the issue.

    Thanks & Regards
  • 0 in reply to Akshaya Dharmajan
    Prodigy 35 points
    Hi Akshaya!

    Hope your project goes well.. : )

    I had several problems on my design and needed to fix them all before got a "stable" value. it seems the ADS1232 is extremely sensible to any noise! no wonder why since it seems to work with low voltages values.

    The first problems was the ground plane and electric stability .. some decoupling capacitors and a good ground place was a must, it improves the stability, however it still was acting funny. I was using a custom PCB design, so I'm not sure if this will help you since it seems you are using an evaluation board

    Then I found that a Bluetooth and WiFi module near the ADS was making a lot of noise, so I turn it off, that helped a lot!.. but since I needed to have them broadcasting. I used a DC/DC converter to isolate the electrical connection between the ADS and the wireless module. AND shielded the ADS and tracks.

    Then short the sensor cables to 6 or 10 cm.

    after all that I have some "stable" value, at least the increasing or decreasing problem was fixed .

    Then I got better quality stain gauges, not those USD $2.00 .

    Next was to fix the sensors to a board, so they aren't moving around and that help to keep them still and at same temperature (check what happens when you heat one or apply cold air)

    It never was a pretty stable raw value. So by software I just take the average of 100 samples and that got me a very good value.

    I'm sorry I don't have a simple and more effective answer, however it took me a while before fix all the issues.
    It seems is just too sensible to external noise, so check the sensor you are using.

    Hope this help you! and hopefully Bob Benjamin can help you a bit more, since the ref board should have a better performance.

    Good Luck mate!