Need help using Pyserial

[deanhystad]

Your program sends "hello" out the serial port. Why? I didn't see anything about having to send a program name to the telescope.

I thought readline() returned zero bytes when it times out. Looking at Pyserial documentation it says readline() is provided by io.IOBase.readline() and when I look there it says nothing about what readline does when it times out. BUT I did notice that read_until() behaves as you described. This would make it a good choice for reading the response.

import serial

NAK = b"\x15"
EOL = "#".encode()

def sendCommand(ser, cmdStr):
    """Send command to telescope.  Prepend : and append #"""
    ser.write(f":{cmdStr}#".encode())

def readResponse(ser):
    """Read response.  Strip trailing #"""
    response = ser.read_until(EOL)
    if len(response) == 0:
        return None
    elif response[0] == NAK:
        return NAK
    if EOL in response:
        response =  response[:response.index(EOL)]
    return response.decode()


ser = serial.Serial("COM3", 9600, timeout=1.0)
sendCommand(ser, "GR")
print(readResponse(ser))

NAK is not zero bytes. NAK is b'\15'.

Writing extra "#" is just going to cause confusion. Your telescope is going to say "I see #, where was the command?" and then it is probably going to return a NAK which you will read thinking it is the response to the command you are trying to send instead of a response to the leading "#".

As I said in my post, I do not have an ETX telescope. I guess to be clear I should say I don't have a Meade telescope and have no way to test the code I wrote. I would be surprised if it works.