I originally wrote code for the MS5541C pressure sensor using bit banging, and described the result of my investigation in the previous log entry.  At the end I mentioned that the sensor’s weird digital interface is kind of like SPI, and looks SPI-compatible, with several differences that could be worked around.  The most notable difference was that reading and writing data happen out of phase with respect to the serial clock edge. It wound up being a little squirrellier than that, but it worked out.  Below is some code for accessing the MS5541C with SPI. It runs on a Seeeduino Mega (which is compatible with the Arduino Mega and uses the ATmega1280 microcontroller), but I’ve eschewed the Arduino libraries for the sake of more control (and, for the ol’ bit-banging, better timing resolution). Some of the code, particularly the SPI stuff, could be replaced with Arduino library calls.
Continue reading →