Characterise Waveshare HP AD/DA board Raspberry PI

Use MATLAB to characterise the high precision AD/DA board for Raspberry Pi from Waveshare.

This MATLAB script runs a test of the Waveshare high precision AD/DA board using the ADS1256 and DAC8532. number of samples "n" and time between samples "dt" can be set at the beginning of the script. dt is generally not accurately enforced by the script. VREF must be input at the beginning of the script. I measured it using a Keithley DMM 6500 61/2 digit multi meter. The source for VREF was a LIPO battery that was stable to within +/- 5uV throughout the test.

The script shows how to access the registers on the ADC and DAC chips directly via SPI through the Raspberry Pi.

The results are shown as a graph of ADC input versus commanded DAC output with a linear fit and analysis of residuals. The results show that the board can be used to within +/- 10mV. There is a definite bias of ~20mV and there is a non-linearity of +2mV/V.

IMPORTANT NOTE: This has only been tested with R2018A and Raspberry Pi server_v18.1.0. It is known NOT to work with R2018B and Raspberry Pi server_v18.2.1 (I have posted this problem, in which R2018B loses the connection to the Raspberry Pi very quickly).