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Uni-T UT61B and Linux

A simple Perl interface to the Uni-T UT61B digital multimeter

 
The :xeyesUni-Trend UT61B Digital Multimeter is a quite sophisticated, but nevertheless economic DMM. It`s features like temperature measurement, display backlight, bargraph and MIN/MAX, RELATIVE and HOLD modes are usually found only on higher class DMMs. In my opinion, several Uni-T multimeters deserve the best-bang-for-the-buck award.
It is quite sturdy as well, and proofs that the Chinese are well capable of delivering good quality, if you ask (and pay) them to do so.
 
The most interesting feature for me was it`s serial RS232 interface, allowing to transfer it`s readings to a computer for further processing or graphical visualization.
Data is written about twice a second. This is a very low rate compared to an oscilloscope, but no oscilloscope can display data other than voltage without additional probes. The UT-61B (and several of it`s cousins) do allow not only voltage, but all of it`s readings (like power, resistance, frequency and temperature) to be transferred to the computer.
Connecting the temperature probe to your coffee pot, and let the computer send you a fax when coffee`s ready? Not really a problem.
 
The supplied software seems simple but functional; however, as usual, it`s for Windoze only. Not acceptable.
 
I found several transfer programs on the net for Linux for the UT60A, the UT70B and the UT61E; but none of them seems compatible with the UT61B`s data output.
So, out comes the Perl toolbox, and after a long night the UT61B is happy to present it`s data to at least (probably) any Unix-like operating system.
 
Thanks to :xeyesHenrik Haftmann, who reverse-engineered some of the :xeyesprotocols, I was able to write a Perl script to connect my DMM to Linux. By the way, people report that Uni-T itself is as well very helpful.
 
The Perl script needs the Device::Serial module, which you can find in the repositories of most Linux distributions, or in Perl`s :xeyesCPAN.
The script basically outputs the values to standard output; you can redirect them to any program or file you wish, for example a csv database or gnuplot to draw a realtime graph.
 
The script does some very basic math, offering optional minimum, average and maximum values, but doesn`t consider the user changing settings while registering data (maybe I`ll implement that). So if you use this option, for now set it to a manual range and don`t switch settings, otherwise the calculated values will be wrong. If you need to do advanced processing, use a spreadsheet or database (or Perl, of course).
There is a very basic graphic function, using gnuplot, and a very basic wrapper that offers the readings on a network. Read the help (-h option), the telnet wrapper has no documentation yet..
 
Bild "ut61b_gnuplot_screenshot.png"
 
It is licensed under the GNU GPL, so feel free to do with it what you want. The restrictions are few: Don`t claim you wrote it and leave the copyright notice, don`t blame me if it breaks something, and if you give it away or change it, offer the source.
 
Download dmmut61b v0.4 :filehere and the telnet wrapper v0.1 :filehere.
 
It is alpha (=early testing) status. I can`t test all values, as for example I don`t have any condensers. If you discover erraneous measurings, please call it with the following options
 
$ ./dmmut61b -v=2 -n=10 -f
 
capture the output, and :thread send it to me with a short description of your DMMs setup. If you cannot get it to run, consider some Perl FAQs on the net.
 
:idee Remember that you have to switch the DMM`s transmission mode to ON...
 
Don`t bother me with any Windows related problems - it`s YOU who chose to use it.
 
Basically, the DMM transmits via an opto-coupler to a serial port or USB-to-serial adapter (2400 baud,8,N,1,RTS+,CTS-). The transmission consists of a 14 byte packet with 12 bytes of data; 5 of them represent the actual measuring, other 4 have single bit flags that resemble the status of the DMM (measured value and power of 10, MIN/MAX etc.).
 
Another interesting idea could be to collect the data using an old Palm Pilot and transfer it later to keep things more pocket friendly. We`ll see.
 
Happy harvesting.
 

Links

 
Uni-Trend :gb
Uni-Trend, the manufacturer
 
Uni-T DMM protocols :de
Henrik Haftmann`s protocol analysis of several Uni-T models
 
Dr. Rolf Freitags Projects :gb
Georg Acher's Homepage :de
Jens Gecius :de
Uni-T UT60E RS-232 Data Logging :gb
UtSixtyEDecoder :gb
VC 840 Recorder for Mac OS X :gb
Linux drivers for the Voltcraft VC-820/VC-840 DMM (aka Uni-T UT60A/UT60E)
 
Steffens Noteblog :de
Linux driver for the Uni-T UT61E (seems to be incompatible with my Uni-T61B)
 
Mario's Homepage - Utdmm :gb
Linux driver for the Uni-T UT70B
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