Question

I get bytes from the serial port which represents the voltage on my PIC board.
But I can’t convert these bytes(strings) to decimal because I get the error message above.
Here is the function(in fact, it’s associated with tkinter button)

def channel8():
    ser.write(chr(0xFF))
    print "you have select channel8"
    x=ser.read(2)
    w=int(x, 16)
    print w
    print "Voltage on channel8 is:" , x

ValueError: invalid literal for int() with base 16: ‘\x0e\xa3’

def channel8():
    ser.write(chr(0xFF))
    print "you have select channel8"
    x=ser.read(2)
    z=struct.unpack("h", x)
    #w=int(z, 16)
    print z

and i get this :

Voltage on channel8 is: (28942,)

can you please explain how did i get this value? it’s not matching anything 😀

Answer 1

I think you should use struct module and unpack your binary data like this:

struct.unpack("h", x)

Because int is not really for working with binary data, but with hexadecimal strings like: EF1D.

When you did x=ser.read(2) you received two bytes of binary data, there are two types of number representation supported by struct library: short(h) and unsigned short(H). Function struct.unpack receives two argument:

• structure specification (a string of format characters)
• binary data

and returns a tuple with unpacked values(only one int in your case).

So you need to change string w=int(x, 16) to w = struct.unpack("h", x)[0] or to w = struct.unpack("H", x)[0], it depends on data type.