Arduino reads bogus from serial

Question

Recently I've started playing around with an Arduino Uno (rev 3), and I've set up a communication bridge between the Arduino and my computer using Python. So I send a command in Python ("ping" for instance), which is then read and interpreted. I've had it working before, using the Python commands to control a motor, but today it became non-responsive. However, only if I boot the serial monitor from the Arduino IDE, it suddenly accepts my commands again. Further inspection reveals that the Arduino is probably reading empty or corrupted data, interpreting it as ð, à and ÿ and such.

Here is an excerpt of the Python code I'm using:

import sys, glob, serial, time, re
class interface:
 timeout = 2 # 10 second time-out
 def __init__(self):
 port = "/dev/ttyACM0"
 self.connect(port)
 pass
 def connect(self, port="/dev/ttyACM0"):
 global arduino
 arduino = serial.Serial(port, baudrate=115200, bytesize=8, parity=serial.PARITY_NONE, stopbits=1, timeout=0.1) # Establishing connection
 time.sleep(3) # Allowing the connection to settle
 arduino.flush()
 print "Connection established..."
 def ping(self):
 arduino.flush()
 arduino.write("ping")
 msg = self.listen_arduino()
 print msg
 if msg == "ping_ok":
 print "pinged"
 return True
 return False
 def listen_arduino(self):
 timeout = self.timeout
 matcher = re.compile("\n")
 buff = ""
 t0 = time.time()
 buff += arduino.read(128)
 while (time.time() - t0) < timeout and (not matcher.search(buff)):
 buff += arduino.read(128)
 return buff.strip()

And here is the Arduino C code:

String readString;
void setup() {
 Serial.begin(115200); // use the same baud-rate as the python side
}
void loop() {
 readString = listen(); // listen for any commands
 if (readString.length() > 0) {
 Serial.println(readString); // print the command
 if(readString == "ping") {
 Serial.write("ping_ok");
 }
 }
}
String listen() {
 String readString;
 while (!Serial.available());
 while (Serial.available()) {
 delay(1); // Allow the buffer to fill
 if (Serial.available() > 0) {
 char c = Serial.read();
 readString += c;
 }
 }
 return readString;
}

I suspect there is something fishy with the connection I'm making on the Python side, as the Arduino IDE serial monitor works just fine. I hope anyone can spot the problem in this code, I'm willing to provide more details on request.

Thanks

• Avamander: Try with one letter. See if that helps.
• evolutionizer: change the code to Serial.available()>0 because by default the output is -1, this could be the reason you are receiving junk values.

Answer 1

I've discovered that there was another program trying to access the Arduino, interfering with the code above and causing corruption of the signal. After terminating the intrusive program, the code worked just fine.