Raspberry Pi High-Precision AD/DA RB-Wav-08 and negative voltages

Help & Support Robot Parts
1

I am trying to use this board to read from 6 analog bipolar input channels. I find inconsistent results when attempting to read negative voltages. According to the ADS1256 documentation, the voltage range is +/-2Vref/PGA, which should be +/- 5V for me. However, the A/D hits a floor of about -0.5V below which it will not read. These are single ended signals wtih a common ground - tied to AINCOMM.

I am using the C-code and bcm2835-1.45 library.

4

Hi,

Was this board bought from RobotShop ?

Can you please send a close up picture of your setup?

5

My bad… While the A/D is capable of measuring +/-5V from its differential inputs, the individual inputs must themselves be greater than 0V., for example, centered at 2.5V. I didn’t read the datasheet of the ADS1256 carefully enough.

Might be worth noting so others don’t misinterpret capability as I did.