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AD7788 Communication

Question asked by EJRarclab on Aug 18, 2014
Latest reply on Sep 18, 2014 by analogman

Hi all,
I'm a student researcher with WPI's ARC Lab. We're a robotics research lab, and one of our research topics is the deformation of objects in a simulated surgical environment.

I should move from the application right on to the question, though. To measure deformation, each object produces an analog voltage that is fed to the AD7788 on its AIN+ channel.

However, I simply cannot seem to communicate correctly to the ADC over the SPI-like protocol. I am using a FRDM-K64F mbed and an Arduino Uno R3 and their respective SPI APIs. I have used these SPI APIs successfully before; it is communicating to the AD7788 specifically that fails.

Here's what the AD7788s are receiving:



I've been unable to convert a test voltage or even successfully read the status or mode registers (logic analyzer confirmed). I am at a loss as to what to do. What do you all think? I'm thinking it must be something I'm doing, rather than the chip, since I'm having this same trouble with multiple AD7788s whether in the application circuit or in a test breadboard.