How to manage multiple pyfirmata arduinos?

[shawnkirsch]

How would I do this?

if I have 3 arduinos hooked up to different things how do I reliably pick a specific arduino.

[shawnkirsch]

i.e.: one for light sensor streaming, one for a robotic controller, one for a different arduino with a servo or something.

in my case need a lot of streaming, so would need specific control.

[David-Lor]

Never tried with more than a single board, but Have you tried declaring the 3 boards? Something like

board1=Arduino("/dev/ttyUSB0") board2=Arduino("/dev/ttyUSB1") board3=Arduino("/dev/ttyUSB2")

[coelhudo]

I tried to use two boards at the same time but didn't work. ~The limitation is the pySerial library~. I still don't know why, but the trick that worked for me is to start two instances of Process from multiprocessing.

from multiprocessing import Process, Queue

def one(queue):
    board_one = Arduino('/dev/ttyUSB0')
    #your code for board one here

def two(queue):
    board_two = Arduino('/dev/ttyUSB1')
    #your code for board two here

q1 = Queue()
mp_one = Process(target=one, args=(q1,))
q2 = Queue()
mp_two = Process(target=two, args=(q2,))

mp_one.start()
mp_two.start()

#interaction between this context and mp_one and mp_two through q1 and q2

If communication is necessary, you can use multiprocessing.Queue as a way to exchange objects between the main process and the other processes as you can see in the example. multiprocessing.SimpleQueue and multiprocessing.Pipe can also be employed to this end.

[tino]

Hmm, strange. If I remember correctly I've used 2 Arduino Mega's at the same time in a project several years ago without spawning multiple processes. But I'd have to dig into my code archive to make sure.

Also pyserial seems to open a file descriptor per serial.Serial class (https://github.com/pyserial/pyserial/blob/master/serial/serialposix.py#L265), so that should work.

Do you run into any specific error?

[coelhudo]

Yes. For example, when I tried the code below only one of the boards worked.

board_one = Arduino('/dev/ttyUSB0')
board_two = Arduino('/dev/ttyUSB1')

#boards setup here, enable_reporting and Iterator stuff

print(board_one.analog[0].read()) #prints None
print(board_two.analog[1].read()) #prints current state of pin A1

If I changed the instantiation order, the opposite occurred: board_one Ok but board_two not Ok.

Just for context, I'm working with Python 3.5.3 on an RPi running Raspbian, communicating with two Arduino Uno.

When I each board is isolated in a multiprocessing.Process instance, everything works fine.

Since I didn't find anything that could cause this problem in pyFirmata code, I searched for similar issues involving pySerial. I found some threads on StackOverflow related to open multiple ports using subprocess, threads, or multprocessing. They weren't stating that the problem was in pySerial per se, but I modified the code with their suggestion, and this did the trick.

You are correct regarding the file descriptor and pySerial, and I made a mistake on blaming pySerial. It was just an assumption. I fixed my previous comment.

Because this solved my problem, I decided not to continue the investigation to find the cause of the problem.

[tino]

Thanks for the clarification and the solution!