Software for the multimeters vc840/vc820

Software for reading the data from the cheap digital multimeter VC 820 (about 50 EUR in 2007) or VC 840 (=VC 820 + True RMS, about 85 EUR in 2007) from with posix commands via a serial port.
They can be combined e. g. with the clamp-on ammeter VC 601 (about 69 EUR in 2007).
Tested with Linux, should work with every posix conforming operating system and Cygwin.

The software should also work with newer VC DMMs, e. g. the VC-830, VC-850, VC-870, VC-920, VC-940 and VC-960. Because the protocoll is compatible with the DT 9062 it should also work with this DMM and successors.
For communication with the PC/Notebook/... also a an USB adapter (with opto coupler) is availible, e. g. at

README for realtime plotting the data for printing the plot as a postscript and a png file

vc840.c is the source code

Example output, with time in seconds since start, voltage and flags:

0.3 -9.300 mV ()
0.7 -9.400 mV ()
1.0 -9.500 mV ()
1.4 -9.600 mV ()
1.7 -9.600 mV ()
2.1 -9.700 mV ()
2.4 -9.700 mV ()
2.8 -9.800 mV ()
3.1 -9.900 mV ()
3.5 -9.900 mV ()
3.8 -10.000 mV ()
4.2 -10.100 mV ()
4.5 -10.200 mV ()
4.9 -10.300 mV ()

The digital multimeter (DMM) can be powered from the USB bus, instead from battery, but the ground of the USB is not the ground (COM) of the DMM input. The ground of the DMM input has a negative voltage.

The MS-Win program provided with the DMM, is very poor and produces binary data files like


and you need special software to get the data in CSV format or read them with a program like MS-Excel. The DB file can be read from MS-Excel, but only with problems like no time.
Conrad offers the DMM PROFILAB SOFTWARE for around 36 EUR which should not have these problems.

GNU-Software for the similar cheap MAS-345 or a Digitek-4000 multimeter, connected through an RS-232 port can be found here:
The multimeters of type Metex M-4650CR are also similar, also at 1200 Baud:

With my first USB-RS232 (USB to Serial Adapter) adapter with an Pl2303 (driver pl2303) i've got the problem that this adapter does nothing after some hours and a user (Stephan R.) reported defect checksums and lost bytes with such an adapter while communication works without problems with an onboard serial port.
I'm now using an USB to Serial Adapter with an FTDI chip (driver ftdi_sio, chip FT232BM) without problems.

Update 2011-11

A newer DMM with one digit more, wider measurement ranges and more serial speed (9600 instead of 1200 Baud) is the Uni-Trend UT61E, for about 47 Euro (including shipping) e. g. on Ebay.
But at some points it's not better: 10 instead of 20 A maximum and no temperature measurement.
Sourcecode for reading the data, plotting with gnuplot etc. can be found e. g. here: