Python Serial communication Arduino (Teensy) to Raspberry Pi

Question

I have managed it to write from my arduino (Uno) to my Raspberry Pi 3 via Serial.

If I use the same python script on the pi side, and the same Sketch on arduino side, but using a Teensy instead, I cant read any output from my Arduino.

Is there any difference between thes arduino Uno and the teensy depending on Serial communication?

Arduino sketch:

void setup() {
  Serial.begin(115200);
}

void loop() {
  delay(1000);
  Serial.println("10.7;0.7;FFFF:FFFF:FFFF:FFFF:");
}

Python script on my Pi:

import serial
ser=serial.Serial("/dev/ttyACM0",115200)
while True:
    print("Waiting for messages from arduino..");
    read_ser=ser.readline()
    print(read_ser)

This code works fine for my Arduino Uno, but not for my Teensy. ttyACM0 is correct in both cases.

OS on the Pi is ubuntu mate 16.04. I can see the output of both arduinos in the Arduino IDE.

I tried this with 3 different Teensies, so the hardware should not be the problem.

Any advices?

** ser.isOpen() is true

bytesToRead = ser.inWaiting() print(ser.read(bytesToRead)) makes no difference.

Could there be a difference, because the teensy is connected with the pi with micro usb, and the UNO is connected with an A to B USB?

You can't read data on teensy if haven't an hardware opening procedure Probable missing points : handshake, additional data for open bus. Dump bus data and you will be see python and terminal data different. — dsgdfg
– dsgdfg, Commented Nov 7, 2017 at 10:17
Arduino have low speed usb-ser but teensy(3.X) got 6Mb/s(i tested) bus. Some high speed devices required additional data before start a communication. — dsgdfg
– dsgdfg, Commented Nov 7, 2017 at 10:41
Don't do this @MoritzSchmidt , unidirectional communication most awful things on communicate with a device. On teensy speed definition Serial.begin(115200); or Serial.begin(0); or Serial.begin(12345678); not important because got 12Mb/s connection if used native port. — dsgdfg
– dsgdfg, Commented Nov 7, 2017 at 18:26

dsgdfg · Accepted Answer · 2017-11-09 07:15:57Z

3

+50

Teensy is an ACM device ? YES !

Got additional BULK IN and BULK OUT ENDPOINTS(Interrupt_dev = 0, CDC_dev=1)

Your Teensy code is very bad (Why calculate and send data if don't need ?)!

For test program like this :

unsigned long s = 0;
void setup(){
    Serial.begin(0);//Not important !(speed 12Mb/s)
    }

void loop(){
    if(Serial.available() > 0){
    while(Serial.available() > 0){//Buffer memory must always be clean !
        char read = Serial.read();
        delay(1);//wait until next_char
        }
    Serial.print("TEST : ");
    Serial.println(s, DEC);
    s++;
    }
}

Python Code :

import thread
import time
time.sleep(20)
#Don't fight with the Kernel, wait some seconds for prepare device

class _CDC :
    def __init__(self):
        self.dev = "/dev/ttyACM0"
        self.query = ""
    def read(self,_passarg):
        with open("/dev/ttyACM0","r") as readBuff:
            while True :
                ans = readBuff.readline()
                if ans:
                    print ans[:-2]#Ignore "\r\n" parts ! 
                #time sleep for save cpu clocks
                time.sleep(0.001)
    def write(self,_passarg):
        with open("/dev/ttyACM0","a") as writeBuff:
            while True :
                if self.query != "" :
                    writeBuff.write(self.query+"\n")
                    self.query = ""
                #time sleep for save cpu clocks
                time.sleep(0.001)

CDC = _CDC()
thread.start_new_thread(CDC.read,(None,))
thread.start_new_thread(CDC.write,(None,))

for i in range(30):
    q = "SEND-TEST%02d"%i
    CDC.query = q+((64-len(q))*"\x00")
    time.sleep(0.1)

Can read write (like a file object) if device is ACM. Open device with "r" and "a" mode for reading last-line.

edited Nov 9, 2017 at 7:15

answered Nov 8, 2017 at 10:06

dsgdfg

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1 Comment

Prof Huster Over a year ago

I am also having trouble reading and writing to a Teensy from a Raspberry Pi. Can you give an example of using the class _CDC? I am confused by your code. What is the arg _passarg for in read and write? Can you give an example of reading and writing like a file?

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