Sending data from serial port

Question

I would like to send one string over the serial port; it works in a loop but not when I send only one string:

I have two Raspberry Pi 2. Each one have a xbee module. I want to send data from one to the other. They are correctly connected.

To test sending data I have this little Python script:

import serial

ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=.5)

while True:
    ser.write('Hello world!\r\n')

My other Raspberry Pi connected with minicom receives correct data:

Hello world!
Hello world!
Hello world!
...

Everything works, but I want to send only one string and remove the loop, however with this code:

import serial

ser = serial.Serial('/dev/ttyUSB0', 9600, timeout=.5)

ser.write('Hello world!\r\n')

I received nothing... I don't know why. Does anyone know what's wrong?

Answer 1

Radio isn't reliable. It can and will get lost if you only send it once. I recommend sending it multiple times and implement a debouncing logic on the receiving side.

Sending sample code:

for x in range(0, 10):
    ser.write('Sending ten times! \r\n')

Receiving sample code:

data_fresh = ser.readline()
data_old = " "

if data_fresh != data_old:
   data_old = data_fresh

   [the rest of your code]

else:
   [ignore or do something if cache data is equal to received data]