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Hacking the Victor VC-921
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itsthatidotagain:
I picked up a Victor VC921 True RMS pocket multimeter to add to my growing pile of ultra cheap (and mildly hazardous) multimeters used mainly for low voltage microcontroller hacking, and naturally the first thing I did was take it apart.



It seems there are at least two variants of this meter, the one I have is the 4000 count "true RMS" variant.

It turns out this meter is based on the DTM0660 chipset, which means  it is possible to hack in a serial port (using an optoisolator IRLED and a 100 Ohm resistor), so that mod was promptly done. NOTE: You will need to update the contents of the 24c02 eerom to switch this on.

More details here.
 
For additional fun, I also modified it to 8000 counts.
It should also be fairy simple to add a Select and Hold button, and perhaps even Temperature modes.

A full set of teardown pictures are available here...



I also added the DTM0660 protocol to QtDMM (a Qt based DMM readout and logger).

Code on Github here.... https://github.com/pingumacpenguin/QtDMM-DTM0660-Version



Enjoy. :-+
tronde:
Some reading from Russia:

While versed with his instrument, a lot of looking for information, came across the instrument baby Victor VC921 several times. Think again failed to include in its frequency device, then buy something else with a frequency counter. VC921 has multiple versions, I was looking for just such where they were and Hold the Select button under the battery cover. ... I bought and upgraded.
ALL WORK MODES!

Scroll down and use google translate
http://kazus.ru/forums/showthread.php?t=112135&page=68

more
http://kazus.ru/forums/showthread.php?t=112135&page=69
itsthatidotagain:

--- Quote from: tronde on August 04, 2016, 10:39:27 pm ---Some reading from Russia:

While versed with his instrument, a lot of looking for information, came across the instrument baby Victor VC921 several times. Think again failed to include in its frequency device, then buy something else with a frequency counter. VC921 has multiple versions, I was looking for just such where they were and Hold the Select button under the battery cover. ... I bought and upgraded.
ALL WORK MODES!

Scroll down and use google translate
http://kazus.ru/forums/showthread.php?t=112135&page=68

more
http://kazus.ru/forums/showthread.php?t=112135&page=69

--- End quote ---
Thanks for that, I had already read it, but it makes interesting reading for those following on. If you look carefully at http://kazus.ru/forums/showthread.php?t=112135&page=69 the image of the DTM0660 based variant includes my knees.  :-DD alvadep has "borrowed" the image from my Google Album here => https://photos.google.com/share/AF1QipPykJgrz2vMySXTkFdst6YsfoTs0Mzs1vmWZXa-XQ5EGBxVeRmFiqj-jO2c44IFcA?key=T01ITXVCa015U0x5WV9UZUV6dUdiSGdXUTBENF93

The rest of those pictures might also help anyone trying to replicate the hack.

This might also be of interest. http://stm32duino.com/viewtopic.php?f=45&t=1296
 
tronde:
Ready for surgery.

As far as I can understand:

Anode of LED to pin 8 on 24c02 and cathode of LED to pin 20 on DTM0660? Series resistor to the most convenient pin.

Make sure I have +3,3V on pin 8 / 24c02 from programmer as a power supply while programming.

Anything else to consider?

pascal_sweden:
Do they also sell a version with all options provided by the chipset enabled by default?

How much does that one cost extra?

Or is that one not sold under Victor but under another brand?
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