From silly lab equipment to best buddies
If you keep up with the blog posts about my senior design project or the boom box, you’d know I’m in an endless battle with the Porsche engineers in trying to communicate with the onboard BMS (Battery Management System) to a Porsche Taycan battery module I scored on eBay for cheap.
For the uninitiated, I’ve been reading hundred-page-long datasheets trying to figure out what components and voltages to provide this battery to try to unlock its cell voltages and temperature, etc. The pipeline is as follows: My MCU sends an SPI message to an MC33664, then the MC33664 converts this message into pulse-encoded SPI known as TPL. This TPL is then passed though a 1:1 isolation transformer and choke into the battery, where it sees another transformer, and then finally the onboard MC33771C, which handles all the battery voltages, temperatures, etc.
At this point, all I’m missing is an isolation transformer for my setup, but I’ve tried to exhaust the scenario in which I can get away without the transformer and communicate with just the MC33664. It doesn’t seem to work without the transformer unfortunately, as I seem to be matching all the timings, and information encoding seamlessly as provided in the datasheet. My assumption is that either my messages are still incorrect and the BMS rejects these messages, or the missing transformer is causing the loss in communication.
However, something has been very useful to me while debugging this, and that’s ECE 310’s Adalm2000. This device is an all-in-one lab tool, with an oscilloscope function, function generator, voltmeter, power supply, and everything between. With the nature of this TPL communication nightmare, it is actually really useful because I can run the oscilloscope and logic analyzer side-by-side on the same device, and see the TPL signals appear just as the SPI pins are clocked. This has confirmed that my message encoding should be up to spec, and leaves me with few options to explore in the process of conquering the communication of this thing.
