Hey guys,
I'm currently scratching my head after doing some probing on a serial bus that I'm trying to hack. There is a button controlled user interface that communicates to a motor controller unit via 4 wires that I have determined to likely be: ~+7V, DATA, Chip Select, and GND.
Sorry in advance for the horrible screen capture, I had to use my phone as I apparently lost my USB stick.
When the user interface is in power-down or sleep mode, the yellow signal is held high at a constant voltage around 7V. When a button is pressed, the interface turns on and the yellow signal starts oscillating at 1kHz as seen in the photo above. The pink signal goes high and is held high until the device goes to sleep. The blue signal, DATA, looks like a typical serial binary protocol with a logic level of 0-~11V. It is only active when the user interface is awake.
I have a few questions about what is going on here. First, why would the power line be oscillating like that? I can't think of what function it could serve between a user interface and a motor control unit. Pressing buttons on the interface does not change the frequency of the oscillations. Second, I'm assuming that this serial interface is just a one-wire interface, because there is no clock signal. I have never seen a one-wire serial interface that operates at ~11V, has anyone here ever come across something like that before? The data line is likely bi-directional, because the motor control unit is capable of sending error codes back to be displayed on the UI. Also, why on earth would the data line be operating at a higher voltage than the power supply line?
My end goal is to be able to replace the user interface with an Arduino to implement my own control system. I'll have to decode the serial protocol and write my own library to serve as a functional replacement, as well as include the appropriate logic level translators between the arduino and higher voltage serial bus.
Just throwing this post out there in hopes that someone could give me some ideas on how this works. Thanks!