Jörg Rädler

Some days ago I was looking for a temperature monitoring solution for some rooms and 19"-racks at the university. The Arexx TL-500 looked promising and I bought it. Unfortunately there are only Windows drivers available. But some people already analyzed the communication protocol and hacked a simple version of a linux driver:

http://www.algorithm-forge.com/techblog/2010/01/linux-usb-driver-for-the-arexx-tl-500-–-part-ii/

There's even a small logger hardware (ARM-based) using this device:

http://rndhax.blogspot.com/2010/03/friendlyarm-mini2440-arexx-tl-500.html

As a python fan I couldn't resist porting this to python to get a small and flexible script. It can be easily extended to save the data, create charts (maybe using matplotlib) or present a web interface.

By looking at the raw data I noticed that bytes 6 and 7 (maybe more?) contain a time value. Maybe it counts the seconds since the initialization of the device?

The first version of my script is mainly a port of the C program. The script uses pyusb 1.0, a python wrapper for libusb 1.0. You may have to install it manually, most linux distributions come with older versions.

#!/usr/bin/env python
import usb.core, array, time
 
def getData(rawData):
        sensor = rawData[3] * 256 + rawData[2]
        tempRaw = rawData[4] * 256 + rawData[5]
        clock = rawData[7] * 256 + rawData[6]
        temp = 0.0078 * tempRaw
        return clock, sensor, tempRaw, temp
 
def collect(dev):
        dataDown = array.array('B', [0]*64)
        dataDown[0] = 4
        dev.write(0x1, dataDown, 0)
        dataDown[0] = 3
        while True:
                dev.write(0x1, dataDown, 0)
                rd = dev.read(0x81, 64, 0)
                if rd[1] != 0:
                        d = getData(rd)
                        print d
                        logData(d, rd)
                time.sleep(10)
 
def logData(d, rd):
        tmp = "\t".join([str(i) for i in rd])
        logfile.write("%s\t%d\t%d\t%d\t%g\t%s\n" % (time.time(),
                d[0], d[1], d[2], d[3], tmp))
 
if __name__ == "__main__":
        dev = usb.core.find(idVendor=0x0451, idProduct=0x3211)
        logfile = open("temp.txt", "a")
        collect(dev)
 

I plan to extend this to a python package using OO, cleaner interfaces, better error handling and more.