Hi there!
Got my hands on a Metrix MX56C, which is said to be compatible
with or identical to the BK Precision 5390. The DMM chip is
referred to as "ASYC-II", see the image in the info box at
https://sigrok.org/wiki/Metrix_MX56C .
Wrote a driver for the "dumb" UART mode where users have to press
the PRINT button. This requires an RX only connection to the PC.
By pressing and holding the PRINT button, users can setup the
update interval (seconds granularity, up to some 10 hours).
PRINT needs to get pressed again each time the function selection
is changed.
Tested the driver implementation with the MX56C and the cable I
had for the Peaktech 3330, in the absence of the genuine cable
for the Metrix meter. The latter is not just a cable, but a
complex kit. Someone had the bright idea to put the IR LEDs
right _under_ the range selector, into the battery compartment.
On a tightly sealed meter with high IP rating. Which was
specifically designed for safety, where one needs to remove the
probes to access the compartment through a front cover. :-O
For the libsigrok patches, see
git://repo.or.cz/libsigrok/gsi.git serial-dmm-asyc-ii
Use the driver like so (PRINT must get pressed before that, or
within a short period of time after starting the command):
$ sigrok-cli -d metrix-mx56c:conn=/dev/ttyUSB0 --continuous
The "smart" mode is much more involved, and requires a cable with
RX _and_ TX, which I don't have.
Though the available literature suggests that all feature/range
selection still occurs on the meter, while the PC can only read
which mode is selected. And might query / re-read next or
previous measurements.
The smart(er) protocol seems to be variable width, highly model
dependent (among a series of DMMs with similar hardware), and
comes with a big red warnings that talking to the meter in ways
that it does not like (in its current mode and state) might
potentially make you lose data. So you had to continuously watch
out for user activity, and adjust communication to the currently
effective mode. Or maybe I'm interpreting the documentation too
strict.
This mode seems to get enabled by pressing a button at power-on.
Apart for the finer/faster update intervals, I don't see a huge
benefit there. The dump PRINT mode provides the level of support
that seems to be typical for many serial DMMs.
virtually yours
Gerhard Sittig
--
If you don't understand or are scared by any of the above
ask your parents or an adult to help you.
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