pyKDC101 0.22

Description:

pyKDC101 0.22

pyKDC101
Functions and examples to control Thorlabs KDC101 through serial.
Mainly for Python, additionally some basic usage for MATLAB.
Here, the controller is used to move a Thorlabs rotation stage (PRM1-Z8).
The interface offered by Thorlabs does not work for unix systems (afaik). Therefore these functions use the low-level serial functionality that is documented in APT_Communications_Protocol.pdf.
Usage
Simply run
pip install pyKDC101

Then in your Python script invoke the functions by
from pyKDC101.pyKDC101 import KDC
kdc = KDC()

With kdc you can then call all functions and methods of the controllers.
Look at example.py. There are a few more commands implemented than shown in the example but they appear not to be too helpful for most applications.
Python
Offers the most used commands (move here, move there, go home) in a simple structure, shown in example.py. Additionally offers a lower-level command structure in which you can send most basic serial commands and read the reply.
MATLAB
I created basic functionalities to test it until it worked but then switched to Python. Still, MATLABthusiasts may find the essential bits in the matlab_KDC101.m-file as guideline to build their own command structure.
Serial ports
By default the openstage()-function will use all the ports found under /dev/serial/by-id/*Thorlabs_Brushed_Motor_Controller* (Windows: COM[0-255], not tested) and try to connect through serial.
You need write-access to the tty-port. Either run as the admin or change the permissions or the ownership on the serial port, preferably with a udev rule, e.g. something like
/etc/udev/rules.d/80-usb-serial.rules
SUBSYSTEM=="tty", MODE="0666"

(After changing run as root: udevadm control --reload-rules && udevadm trigger)
Commands
There are a lot of tricks in getting this to work. I try to document most of it in the code.
Communication basics

The address '01' is the host (usually the computer)
The address '50' refers to generic USB device
When using commands with parameters, '50' needs to be OR'd with '80' leading to 'D0'
While we create the commands in hex, they are converted to integers and sent in binary format
If you are not familiar with serial: be advised to add a delay between sending a command and receiving data (e.g. 50 ms)

Angle to EncCnt conversion


The position parameter structure is encoded in 4 Byte signed little endian, e.g. "64 00 10 00"


To get the number, you have to flip the byte sequence and then convert it:


00 10 00 64 = 0000 0000 0001 0000 0000 0000 0110 0100 =


2^20 + 2^6 + 2^5 + 2^2 = 1048676


Divide this by EncCnt/deg yields rotation in degree: 1048676/1920 = 546 degree


Hence to calculate the needed parameter, you take your angle, multiply it with


the EncCnt/deg, convert it to binary (filling up to 4 bytes). Then you


flip the sequence of the four bytes.


License
This project is licensed under the MIT license.
Acknowledgement
This is under development but I hope it will be helpful for fellow linux-users. Comments and suggestions highly welcome.