问题

I'm working on a project in which I have to receive some 25 character data at a time in order to process it in Raspberry Pi. Here is the example code that generates some data I want to receive from Arduino:

char i =0;
char  a =0;
char b=0;


void setup(){

 Serial.begin(9600);
 for(i=0;i<25;i++){

    Serial.print('l');}
    Serial.print('\n');
    delay(2000);
}


void loop(){

 for(i=0;i<25;i++){
     for(a=0;a<i;a++){
      if((a==9)||(a==19)||(a==24))
          Serial.print('l');
      else
          Serial.print('d');   
     }
     for(b=0;b<25-i;b++){
          Serial.print('l');
     }


     delay(2000);
  }
}

It sends a line like this 'llllddddllldddd...' This line is 25 characters length. Now, I want to receive this with Raspberry Pi. Here is the code I'm trying to work:

ser = serial.Serial('/dev/AMA0',9600,timeout=1)
ser.open()

try:
   serial_data = ser.readline()
   print serial_data
except serial.serialutil.SerialException:
   pass

This code receives data very correctly for like 5 seconds, and then suddenly stops receiving.

Moreover, when I try the following, I get no output, or Input/output errors.

serial_data = ser.readline()
print serial_data

EDIT1: Okay, I commented the exception now. It gives the following error:

 raise SerialException('device reporst rediness to read but returned no data (device disconnected?)')
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected?)

What is the correct way to receive a 25 character data from arduino into raspberry via PySerial? Any help will be greately appreciated.

回答1:

I had the same problem and was breaking my head for a good time, try this

Run

ps -ef | grep tty

If the output looks anything like

root      2522     1  0 06:08 ?        00:00:00 /sbin/getty -L ttyAMA0 115200 vt100

Then you need to disable getty from trying to send data to that port

In order to use the Raspberry Pi’s serial port, we need to disable getty (the program that displays login screen) by find this line in file /etc/inittab

T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

And comment it out by adding # in front of it

#T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100)

To prevents the Raspberry Pi from sending out data to the serial ports when it boots, go to file /boot/cmdline.txt and find the line and remove it

console=ttyAMA0,115200 kgdboc=ttyAMA0,115200

Reboot the Raspberry Pi

Credit where credit is due: http://blog.oscarliang.net/raspberry-pi-and-arduino-connected-serial-gpio/ helped me figure out how to diable getty

回答2:

I had to struggle with this when reading gps data in raspberry pi. The output would stop after about 10seconds and report

 device reports readiness to read but returned no data (device disconnected?)

The solutions given in almost all forums are for raspberry pi 2 with wheezy. I finally managed to get continuous gps streaming in my raspberry pi3 with jessie by doing the following:

set enable_uart=1 and add dtoverlay=pi3-disable-bt in /boot/config.txt. then reboot
I had to change my /boot/cmdline.txt to

dwc_otg.lpm_enable=0 console=tty1 console=serial0,9600 root=/dev/mmcblk0p7 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait

then reboot
stop getty: sudo systemctl stop serial-getty@ttyAMA0.service

to disable: sudo systemctl stop serial-getty@ttyAMA0.service

You need to be careful with the /boot/cmdline.txt. Any mistake in the file may make your raspberry pi to not boot. It is better keep a backup of the file before editing. Also set the baud rate properly. In my case, it was 9600. Hope this helps!

回答3:

I used to get this a lot, and then a friend told me to prompt the arduino for data from python.

Description below

consider having the arduino only send data when prompted by your python program:

prompt.py

#!/usr/bin/python
import serial, time
ser = serial.Serial('/dev/ttyACM0',  115200, timeout = 0.1)

#if you only want to send data to arduino (i.e. a signal to move a servo)
def send( theinput ):
  ser.write( theinput )
  while True:
    try:
      time.sleep(0.01)
      break
    except:
      pass
  time.sleep(0.1)

#if you would like to tell the arduino that you would like to receive data from the arduino
def send_and_receive( theinput ):
  ser.write( theinput )
  while True:
    try:
      time.sleep(0.01)
      state = ser.readline()
      print state
      return state
    except:
      pass
  time.sleep(0.1)

f = open('dataFile.txt','a')

while 1 :
    arduino_sensor = send_and_receive('1')
    f.write(arduino_sensor)
    f.close()
    f = open('dataFile.txt','a')

prompt.ino

void setup () {   pinMode(13, OUTPUT);   Serial.begin(115200); } 
    void loop() {

  if (Serial.available())    {

     ch = Serial.read();

     if ( ch == '1' ) { 
       Serial.println(analogRead(A0)); // if '1' is received, then send back analog read A0
     } 
     else if (ch == '2') {    
       digitalWrite(13,HIGH); // if '2' is received, turn on the led attached to 13
     } 
     else if (ch == '3') {
       digitalWrite(13,LOW); // if '3' is received then turn off the led attached 13
     } else {
       delay(10);
     }
   }    
}

Also, I made a github repository that has some further examples for python-arduino communication:

https://github.com/gskielian/Arduino-DataLogging/blob/master/PySerial/README.md

回答4:

During your loop function in your Arduino code you never end an newline char \n, this is only a problem with ser.readline() because it reads until a \n character.

During your setup function you correctly send a \n character which could explain the intial value being sent, but not the data.

perhaps modifying your Arduino code like this:

void loop(){
    for(i=0;i<25;i++){
        for(a=0;a<i;a++){
            if((a==9)||(a==19)||(a==24)) {
              Serial.print('l');
            } else {
                Serial.print('d');   
            }
        } /*end for loop a*/
        for(b=0;b<25-i;b++){
            Serial.print('l');
        } /*end for loop b*/

        Serial.print('\n'); // CODE EDITED HERE
        delay(2000);
    }    
}

And your python code like so...

ser = None
try:
    ser = serial.Serial('/dev/AMA0',9600,timeout=3)
    ser.open()

    while True:
        try:
            serial_data = ser.readline()
            print serial_data
        except:
            pass
except:
    pass    
finally:
    if ser:
        ser.close()

回答5:

Try sudo rasbpi-config, choose interface option, say 'no' to first message ("kernel login"), 'yes' to second message ("serial communication on"). I found if the first message is on it throws errors. Saying 'no' fixes it.

来源：https://stackoverflow.com/questions/20107700/serial-receiving-from-arduino-to-raspberry-pi-with-pyserial-stops-after-a-while

标签

python