Battery voltage values over serial port over usb.

Capture d'écran de 2016-03-07 21:52:41

Just added a display of each battery voltage. It will be more usefull than I though for the development of the balancing algorithm. If it is possible to balance before charging it could be best solution. Because it removes completelly the capcitive effect. However if a battery is too low the passive draining of the batteries must not go to this level.

By balancing before charging, you wait for the balancing to finish when maybe you need to charge the car quickly. But if the pack is not too umbalanced or too low, it may be a reliable solution.

Also added a CRC to the transmited frames in order to be more confident in the transfered data. I do ont trust that much a serial port. On the linux side, it has his own thread and a stop char but a CRC does no harm.


BMS simulation

Capture d'écran de 2016-03-04 14:49:15

How to make a BMS simulator to test the AVR program? I wanted to keep the original AVR sources but test them as a linux app. I decided to separate the hardware and pure software sides of the BMS program. I modified the source code such that everytime the hardware is used, it is through a C function with no hardware includes. Therefore replacing the hardware C function calls to software C++ simulations and calling the state machine in a loop makes a simulator. I needed to add a graphic view of the battery packs (made with the SDL2 graphic calls) and voilà.

The BMS has a USB serial port to be able to update firmware and to communicate the battery information. This could be simulated with the tty simulator interface included in Linux. But I stayed with my first idea of using a named pipe. Because when created with mkfifo, you chose the name of the pipe, no need to pass it to the second app. I just needed two named fifos in /tmp/, one for each direction. I implemented them in a child class of the serial communication class. In that way the “BMS manager” app can dialog with the simulator or with the real hardware with the same functions.

Simulation speeds up the development process. Because it is easier to recompile and run from the PC than having to turn on and off switches on the battery pack test setup. I had a ton of bugs and still have to clean shit. I prefer bugs in the simulation than fearing of a balancing error killing batteries on the real hardware.

As you can see on the picture, the simulator allows to plug/unplug the charger, run/stop the motor, and change temperature. It is easy to check the diverse safety cases.

The GUI is coded with FLTK. From the internet pages about FLTK it looked like it only suports OpenGL 1.5 but in fact I ported the 2D drawing library using OpenGL 2.0 from Scoreview and it worked fine. So FLTK has this common point witht he SDL: it gives an OpenGL context directly.

And finally I burnt my 2 AD7280A, when installing the board on the test battery pack. I had reverse currents going up the AD7280A  and down to the µController (confused a via silkscreen circle with the 1 pin dot and mounted the ships with a -90° angle). I changed the design anyway, the fact that it is powered by the battery itself makes subtle changes from a standard design for a car.