[Tutor] Serial communication problem

[Phil]

Thank you for reading this.

I've come to the end of my limited abilities with this and I know that 
this is a long shot but someone may spot an obvious error. Two days of 
Internet searching has not led to a solution.

This code sends a "1" and "0" to a pico board to turn it's LED on and 
off. So far so good and this works.

This code then waits for the pico to send "ok" as an acknowledgement. 
This also works.

Next, this code sends an "s" asking for the LED's status. This where the 
problem is. The pico does not receive the "s", yet the "1" and "0" are 
received using the same read method.

It seems to me that perhaps the serial mechanism is missing something 
between sending characters, receiving a response and then sending 
another character.

Initially, I thought that using the " with" block may have been the 
cause of the problem but it's not.

import time

from serial_write import SerialWrite # these are my simple classes 
containing a write, a read
from serial_read import SerialRead # and close methods

# header byte to indicate start of response
HEADER_BYTE = "ok"

with SerialWrite("/dev/ttyACM0", 9600) as ser_write, SerialRead(
     "/dev/ttyACM0", 9600
) as ser_read:

     while True:
         for char in (b"1", b"0"):
             ser_write.write(char)
             time.sleep(1)

             # Wait for header byte to indicate response is ready
             while True:
                 print("in the loop")
                 byte = ser_read.read()
                 print(byte)
                 if byte == HEADER_BYTE:
                     print(f"after if: {byte}")
                     ser_write.write(bytes("s", "utf-8"))  # b"s")
                     break

             print("outside the loop")
             # Read the actual response data
             # data = ser_read.read()
             time.sleep(2)

             data = ser_read.read()
             print(f"Received: {data}")

             time.sleep(1)
             print()
             print()

If it helps, this code prints:

in the loop
ok
after if: ok
outside the loop
Received: ok

The last line should the LED's status and not the acknowledgement "ok"

-- 
Regards,
Phil