I need to read a load cell, trying to do it with the greatest simplicity possible for physically assembling things together.
Load cell puts out 2mV/V at full scale, so if I excite it with the 3.3volt supply from the teensy I will be reading a nominally 1.65volt signal with a +-6.6mV differential.
I want to know if I can use the ADC library with a differential measurement, internal 1.2volt reference and the PGA with a gain of 64 (so differential voltage will be +- (6.6mV * 64 = 422mV).
I would then also measure the 3.3volt supply with a ~10:1 voltage divider to another differential ADC channel with the 1.2volt internal reference so I can compensate for drift and inaccuracy between the two.
My questions:
1. This setup would mean I'd be reading a differential voltage of less than the 1.2volt reference, but the absolute level of both the positive and negative side of that differential would be higher than the 1.2volt reference (but less than 3.3)
Is that acceptable?
2. Are there any other obvious pitfalls to doing things this way?
For reference I'm trying to get about .1% resolution, and ~1% accuracy. This is for a datalogger that will be logging at ~100Hz so I can take many data points and average them together. I'd rather not average together the entire 10milliseconds between data points, but I think if I average however many ADC readings I can take in say 1 or 2 milliseconds that still leaves me with quite a few ADC readings (I'll have to test to see how many).
Bridge resistance is ~200ohms.
Load cell puts out 2mV/V at full scale, so if I excite it with the 3.3volt supply from the teensy I will be reading a nominally 1.65volt signal with a +-6.6mV differential.
I want to know if I can use the ADC library with a differential measurement, internal 1.2volt reference and the PGA with a gain of 64 (so differential voltage will be +- (6.6mV * 64 = 422mV).
I would then also measure the 3.3volt supply with a ~10:1 voltage divider to another differential ADC channel with the 1.2volt internal reference so I can compensate for drift and inaccuracy between the two.
My questions:
1. This setup would mean I'd be reading a differential voltage of less than the 1.2volt reference, but the absolute level of both the positive and negative side of that differential would be higher than the 1.2volt reference (but less than 3.3)
Is that acceptable?
2. Are there any other obvious pitfalls to doing things this way?
For reference I'm trying to get about .1% resolution, and ~1% accuracy. This is for a datalogger that will be logging at ~100Hz so I can take many data points and average them together. I'd rather not average together the entire 10milliseconds between data points, but I think if I average however many ADC readings I can take in say 1 or 2 milliseconds that still leaves me with quite a few ADC readings (I'll have to test to see how many).
Bridge resistance is ~200ohms.