Why is the first values read from the arduino always None

[martynwheeler]

I am trying to read analog data from the arduino. Whenever I read the data the first value is always None. Subsequent readings are okay. I have implemented a check in my code but i was wondering why this was the case.

Here is my code:

#!/usr/bin/python3
# Import Libraries
import time
import pyfirmata

# Creates a new board
board = pyfirmata.Arduino('/dev/ttyAMA0')

# Start the iterator
it = pyfirmata.util.Iterator(board)
it.start()

# Setup the analog pin
analog_input = board.get_pin('a:0:i')

# get the data
try:
    analog_value = analog_input.read()
    while analog_value == None:
        analog_value = analog_input.read()
        time.sleep(0.1)
finally:
    board.exit()
    it = None

print(analog_value)

I have tried waiting 1 second before the first reading but this makes no difference

Thanks

Martyn

[JeS24]

@martynwheeler I think, this answers the "how" of your question: https://github.com/tino/pyFirmata/issues/57#issuecomment-381686268. In particular, "read() can return None in the beginning when there aren't any reads yet.".