Reducing noise in ADS1231 load cell circuit

Hello!

I'm working on a project where I'm trying to measure weight using a load cell from a small, high-precision (0.01g) scale.

I've obtained an ADS1231 to get a 24-bit reading from the load cell. I've sourced an excellent library from this thread which works very well.

I have set up the circuit as indicated in the ADS1231 datasheet:

Obviously I'm using an Arduino instead of the chip in the diagram. I also couldn't get my hands on 1uF caps for the power rails so I'm using 0.1uF ones.

Everything at the moment is set up on a breadboard using jumper wires.

Currently I'm only getting around ~12 bits of precision when I should theoretically be able to reach 17.4 as per the datasheet.

I'm very much a beginner with electronics. I understand that in an application like this, even small factors can create a lot of noise, so my question is: What steps can I take to reduce the noise in this circuit? Every additional bit is valuable to me. Will mounting on PCB make a big difference? Shortening the wires? Adding additional caps?

Thank you very much for your time.

Hi !

With such a cell and 24 bit A/D, keep in mind that you're playing with nV (nanovolts) !

Any source of noise has to be considered.

  1. power supply. Don't use the Arduino power supply, it's noisy. Best would be to have a low noise supply, but that's easier to say than to do.
    In any case, you should use the recommanded 1uF (at least) and not 0.1uF !

  2. The construction. Breadboarding is fine but not for your application. You have to make a carefully designed printed board with clever ground planes. Again a story in itself !

  3. Wiring. Reduce length as much a possible and use shielded wires with ground connections. Otherwise, your wires will act as antennas, and that's not what you want to do. Try to make a GSM call close to your actual setup and you will understand !

These are the first steps you should consider !

You probably wil find some usefull information in the datasheet (which i haven't read)

Cheers,

I was looking at the ADS1220 some time back, even did a board layout. Turned out that I need a 5V sensor so the layout I have has not been built. I have not had a chance to modify it yet. Anyway, it shows in part what I got from looking at the datasheet, and I found an example in the wild as well. It was supposed to be a general purpose connection that could be used with an RTD, thermocouple, or load cell.

ADS1220RatioBridge.PNG

ADS1220RatioBridgeOnBoard.PNG

Well, it certainly sounds like I have my work cut out for me (especially considering I have no experience with PCB production or design!)

I have another question. I only really need a lot of precision in a narrow weight range - I'd say about +15g from the calibration point. Is there any way I can use this to my advantage?

You will never get satisfactory results with a loose wire and breadboard configuration – too much noise.
Consider using the HX711 load cell amplifier on a breakout board. It is best to put the entire circuit in a grounded metal container.

Some breakout boards also feature electrostatic shielding of the sensitive circuitry.