why slow serial start between raspberry pi and arduino?

Question

Hi I'm trying to setup communication between an arduino and a raspberry pi through a usb connection but I am encountering a few strange problems that I just can't seem to fathom. I want to send some data from a python script to the arduino then have the arduino light an Led.

Edit* I have resolved this problem but I'm leaving the question here incase it help someone else. The problem was the serial initialization time. See below

Python code.

import serial
import time

ser = serial.Serial('/dev/ttyACM0', 9600, timeout=3)
ser.open()
ser.write('1')

arduino code

char serialRecieved;



/*output*/
int ledOne=8;
int ledTwo=12;
int ledThree=13;

/*input pins*/
int thermistor=1;

void setup(){
  pinMode(ledOne, OUTPUT);
  pinMode(ledTwo, OUTPUT);
  pinMode(ledThree, OUTPUT);
  Serial.begin(9600);
 }


void loop(){
   if (Serial.available() > 0) {
 
         serialRecieved=Serial.read();
         if(serialRecieved=='1'){lightLed(8,1000);}
         if(serialRecieved=='2'){lightLed(12, 1000);}
         if(serialRecieved=='3'){lightLed(13 , 1000);}
         if(serialRecieved=='4'){sendTemp();}
         delay(1);
   }
}

void lightLed(int led, int time){
     digitalWrite(led, HIGH);
     delay(time);
     digitalWrite(led, LOW);
 }

void sendTemp(){
  int temp=analogRead(thermistor);
  Serial.print(temp);
  }

When I run the python script as far as I can see the led on pin 8 should light up but it doesn't. The strange thing is that if I run a loop(see code below), It works fine except the serial data in the first iteration of the loop is not processed.

this script works except not first loop iteration

import serial
import time


ser = serial.Serial('/dev/ttyACM0', 9600, timeout=3);
ser.open();

i=0
while i < 5:

ser.write('1')
ser.write('2')
ser.write('3')
ser.write('4')
time.sleep(1)
serial_data = ser.readline()
print("temperature")
print serial_data

i=i+1

Does anybody have any ideas why the first part of the serial data is either being lost or not read? By the way if you cant tell already I'm new to python, linux pi and arduino , sorry!

EDIT, PROBLEM SOLVED

Ok I just found the problem, it was due to the time it takes to set up the serial connection between the pi and the arduino. If anybody is suffering from the same problem here's the link.

http://playground.arduino.cc/interfacing/python

Now I just need to find out how to know when the serial connection is ready to start sending and receiving data.

Zoltán Haindrich Zoltán Haindrich · Accepted Answer · 2016-06-30T17:50:16

connecting to the serial line may trigger a device reset(this depends on the used serial converter)...to invoke the bootloader;

this feature is used to load new sketches into the board...usually the board stays in the bootloader for ~1sec and starts the main application if there are no commands - or they are invalid.

if you would like to disable this feature..disconnect the dtr line on the serial converter - but in this case you will also loose the ability to upload sketches...you have to manually push the reset button during every upload cycle.

wow...there is an intresting doc on this topic:

http://playground.arduino.cc/Main/DisablingAutoResetOnSerialConnection

why slow serial start between raspberry pi and arduino?

this script works except not first loop iteration

1 Answers