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Topic: arduino and pyserial (Read 6937 times) previous topic - next topic

Grumpy_Mike

Thanks for amending the post.


that is all the code.

If it is then how do you know it is not working? Is ther some error message that you have not been telling us about?

I would have expected to see a print statement somewhere to display what you got.

Go for just receiving one byte and printing it out.
When you open the buffer flush it to clear any stuff that the arduino has been spitting out.

Remember what python is receiving are characters they are not numbers yet until you convert them.

powergolden

I dont know if you know python or not, but when i do
Code: [Select]
data = arduino.read(20)
hi = data[0]

it tells me the output. Heres what i did to test it.

On The arduino:
Code: [Select]
void setup() {
  Serial.begin(9600);
}
void loop() {
  Serial.print(300);
  Serial.print(',');
}


on python:
Code: [Select]
import serial
arduino= serial.Serial('COM3', 9600)
data = arduino.read(20)
hi = int(data[0])

depending on what i set "hi" to it gives me a different number. It will change even though all numbers printed on serial should be alike.  If you need a example ask But while you respond i will be working on getting them.

powergolden

Heres those examples

input >>> data = arduino.read(21)
input>>> data
b'00,300,300,300,300,30'

i>>> data = arduino.read(20)
>>> data
b'0,300,300,300,300,30'

>>> hi = int(data[1])
>>> hi
44

>>> hi = int(data[2])
>>> hi
51

>>>

Grumpy_Mike

#18
Aug 27, 2014, 12:07 am Last Edit: Aug 27, 2014, 12:11 am by Grumpy_Mike Reason: 1
Quote
I dont know if you know python or not, but when i do it tells me the output. Heres what i did to test it.

So this is in the direct mode from the console?

When you send
Code: [Select]
Serial.print(300);
You will send the ASCII codes 0x33, 0x30, 0x30. In decimal these will be 51, 48, 48
You are sending them very fast so you are filling up the buffer.

Quote
depending on what i set "hi" to it gives me a different number.

You need to say what the numbers are to make any sense of this.

Edit. Just seen your results, does this make sense to you now?
Comma is 44 in decimal as well. so it is working you are just not converting them correctly.

powergolden

So. not to rush it or anything, but how would i fix it and send numbers like this across? Would you recommend breaking the numbers down before sending them? But after I break them down then what? Sorry BTW for being a total Noob at this.

Grumpy_Mike

#20
Aug 27, 2014, 12:26 am Last Edit: Aug 27, 2014, 12:27 am by Grumpy_Mike Reason: 1
At the moment the only thing that separates your numbers is comma, yuo extract a number like this you read the serial port one bit at a time until you find a comma, that marks the end of your last number. Then you gather bytes into a list until you get another comma, don't add that to the list. Then you convert each byte from the character into a number with an (ord(data[0]).
For each successive number you then multiply the previous number by ten and add the next byte to it.

Bottom line is you have to think about what data format you are sending and how you communicate with the arduino.

This bit of code I used to get two 16 bit ints from the arduino. Each byte was tagged with a unique top two bits so I could identify them.
Code: [Select]

def openPort():
      global running
      ser.flushInput()
      # tell the arduino to start sending
      running = True
      ser.write('3')
      ser.write('G')
     
def checkInput(b): # see if the bytes have been received in the correct order
      correct = True
      for i in range(0,4):
           #print i," - " # ,hex(ord(b[i]))
           if (ord(b[i]) >> 6) != i :
              correct = False
      return correct
           
def getData():
  global reading, running
  if running :    
       a = ser.read(4)        
       if checkInput(a) :
           reading[0] = ((ord(a[0]) & 0x1f)<< 5) | (ord(a[1]) &0x1f)
           reading[1] = ((ord(a[2]) & 0x1f)<<5) | (ord(a[3]) &0x1f)
           #print reading[0]," - ",reading[1]
       else:
           correct = False
           while correct == False : # resyncronise
               print "lost sync ",ser.inWaiting()
               b = ser.read(1)
               t = a[1] + a[2] + a[3] + b[0]
               a = t
               correct = checkInput(a)



The code is from my book:-
http://www.thebox.myzen.co.uk/Raspberry/Pi_Projects.html
Which describes both the arduino code and the python code. You should be able to down load both from the book's web site.
It is chapter 16.

Quote
Would you recommend breaking the numbers down before sending them?

You have no choice the numbers are sent only one byte at a time by the hardware so they are broken down.

Robin2

The demo I linked to in Reply #9 works in both directions. Have you got that to work?

This newer demo shows how you can send binary data from Python to the Arduino. The same concept could also be used in reverse.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

powergolden

I would be testing out my code but i keep getting this error when attempting to import pyserial:


Traceback (most recent call last):
  File "<blender_console>", line 1, in <module>
  File "C:\Python33\serial\__init__.py", line 19, in <module>
    from serial.serialwin32 import *
  File "C:\Python33\serial\serialwin32.py", line 12, in <module>
    from serial import win32
  File "C:\Python33\serial\win32.py", line 196
    MAXDWORD = 4294967295L # Variable c_uint
                         ^
SyntaxError: invalid syntax

Robin2

Two or three hours spent thinking and reading documentation solves most programming problems.

Grumpy_Mike

That looks like a windows problem. Unfortunately for you I have only used Python under Linux.

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