I have 4 x 3wire load cells from a old weight scale connected as a full-bridge and I want to connect them in my uC ( Atmega328P, but not arduino ).
I want to measure weight under these specs:
- Precision is the first most important spec
- Error due to sensor is not important. I will change them in the future.
- Measuring 0-200kg ( Each load cell is 50 kg so 4x50 = 200kg. Am I right? )
- 5g resolution ( calculated 16bit ADC = 3,052g )
- I2C interface ( ADCs: LT2451, ADS1113 or similar )
- Update: Load cells work at 3-6Volts
In most of similar ADCs IC there is a programmable gain amplifier capable of gaining up to 8 times. Some have external some internal Vref.
I would like guidance in these areas:
- Vref source
- Use 3.3 Volts from DC-DC converter?
- Use uC Aref pin?
- Use new IC voltage reference?
- Best method for minimizing signal error
- Use PGA provided by ADC?
- Use instrumental amplifier?
I have no great expierience in ADCs but from my point of view I see it as using the smallest Vref source i can find that is also bigger than the bridge output( 200 milli Amps ) and having a opamp before the ADC with a fixed gain and not just putting PGA which is max 8 times.
I find it a little complicated task so I seek guidance in learning from the process...
What I understood so far is that I get a 20bit or bigger ADC in order to minimize the error use Vref from a voltage reference dedicated IC and use no amplifier. If there is a better answer I will wait some days. Am I right? Feel free to edit this assumption if I made a mistake.
After some thought I do not like having 20bit ADC for error free signals. There must be a more professional way to do my math.