Communicating with Arduino and Python via CmdMessenger, not working

Question

I implement a simply CmdMessenger example to permits Arduino communicate with PC via serial port.

The program intent to listen to serial waiting for the command '0;'. When this command is typed, Arduino reads a temperature sensor and write temperature result to serial.

It work's fine from serial monitor, but I cannot use it with PYthon using pySerial. I think I'm doing something wrong in python implementation, below is the code snippet: EDiTED: the code below runs as expected if I run in debug mode (on PyCharm). I put a breakpoint at beggining on this line:

    if (not self.serialConnection.isOpen()): ...

and run with 'Resume Program' from there and it works. I don't know why it don't run in 'Normal Mode'.

import serial
import time

class Temperature:
    def __init__(self, comPath='/dev/ttyACM0', bauds=115200):
        self.serialConnection = serial.Serial(comPath, bauds, parity=serial.PARITY_ODD, stopbits=serial.STOPBITS_TWO,
                                              bytesize=serial.SEVENBITS)

    def queryTemperature(self):
        if (not self.serialConnection.isOpen()):
            self.serialConnection.open()

        # prints True:
        print self.serialConnection.isOpen()
        self.serialConnection.write("0;\n")
        time.sleep(2)
        while self.serialConnection.inWaiting() == 0:
            pass
        # don't reach this point. It stops on loop above
        time.sleep(2)
        iw = self.serialConnection.inWaiting()
        temp = (self.serialConnection.read(iw))
        self.serialConnection.close()
        return temp

and the call of the method queryTemperature:

from temp_read import *
dObject = Temperature('COM3')
print dObject.queryTemperature();

the program doesn't finish. It seems that it stops on the loop:

        while self.serialConnection.inWaiting() == 0:
            pass

bellow is the arduino sketch:

#include <CmdMessenger.h>
#include <OneWire.h>
#include <DallasTemperature.h>

int pinTemp = 13;

CmdMessenger cmdMessenger = CmdMessenger (Serial);
OneWire oneWire (pinTemp);
DallasTemperature sensors (&oneWire);


enum {
  kReadTemperature,  
  kStatus,
};

void attachCommandCallbacks (){
  cmdMessenger.attach (onUnknownCommand);
  cmdMessenger.attach (kReadTemperature, onReadTemperature);  
}

void onStatus (){
  Serial.println ("status");

}

void onUnknownCommand (){
  Serial.println ("unknow");
}

void onReadTemperature (){
  Serial.println ("readTemp");
  sensors.requestTemperatures();
  delay (1500);
  float temp = sensors.getTempCByIndex(0);        
  cmdMessenger.sendCmd(kStatus, (float) temp);

}

void setup() {
 Serial.begin(115200); 
 sensors.begin ();
cmdMessenger.printLfCr(); 
  attachCommandCallbacks();


}

void loop() {
  cmdMessenger.feedinSerialData();


}

Answer 1

It's not using your code, but to achieve the same functionality, I have written a robust python interface to CmdMessenger ( https://github.com/harmsm/PyCmdMessenger ). You could use it to do this task by:

import PyCmdMessenger

# set up serial connection at proper baud rate
a = PyCmdMessenger.ArduinoBoard('/dev/ttyACM0',baud_rate=115200)

# list of commands at top of sketch, with argument formats
commands = [["kReadTemperature","f"],
            ["kSendTemperature","f"],
            ["kStatus","s"]]

cmd = PyCmdMessenger.CmdMessenger(a,commands)
cmd.send("kReadTemperature")
print(cmd.receive())

The changes to your arduino sketch would be adding kSendTemperature to your initial command enumeration:

enum {
      kReadTemperature,  
      kSendTemperature,
      kStatus,
};

replacing your send command so it sends the float as a binary string:

//cmdMessenger.sendCmd(kStatus, (float) temp);
cmdMessenger.sendBinCmd(kSendTemperature, (float) temp);

and removing the extra Serial.Println(XXX) commands.