Author Topic: Victor 921 pocket dmm - reviewed by toddfun.com ($11 on ebay)  (Read 2154 times)

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Offline retiredcaps

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Victor 921 pocket dmm - reviewed by toddfun.com ($11 on ebay)
« on: February 20, 2016, 06:53:46 am »
Todd, a member here, did a review of the Victor 921 pocket multimeter in this video.



BTW, you can this meter off ebay.com for about $11 USD + free shipping vs $25 at Adafruit.
« Last Edit: February 20, 2016, 06:57:06 am by retiredcaps »
 

Offline HAL-42b

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Re: Victor 921 pocket dmm - reviewed by toddfun.com ($11 on ebay)
« Reply #1 on: February 20, 2016, 09:06:15 am »
I really like that!

Not only as a small multimeter but it can be used for building all sorts of gadgets. For example if you rip the leads off you can fit some front end inside he probe well and have a dedicated meter for all sorts of stuff.

Some ideas for possible front ends: uCurrent, Wattmeter, uWattmeter, RF power meter, RCL meter, ESR, all sorts of bridge circuits and what not... Lots of possibilities.

Besides you can just nail a few of them to your workbench wall as rudimentary meters.
 

Offline mos6502

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Re: Victor 921 pocket dmm - reviewed by toddfun.com ($11 on ebay)
« Reply #2 on: February 20, 2016, 11:20:21 am »
Wow, that hard case design is great. That would be a nice meter for keeping in your car or your toolbox. Great functions for automotive stuff. It even has a rel function. :o
for(;;);
 

Offline hugatry

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Re: Victor 921 pocket dmm - reviewed by toddfun.com ($11 on ebay)
« Reply #3 on: July 23, 2016, 02:10:42 pm »
I ordered one from Aliexpress for $9 shipped and received it yesterday. Built quality isn't good, but thanks to the features and hackability, I'm still happy that I bought one. Having each function on separate selector switch position is very nice idea, the probe well and the lid are also something I really appreciate in a pocket multimeter.

User "itsthatidotagain" told in the UT210E -topic that this multimeter most likely has same main IC as what is used in 6000 count DMMs like Uni-T UT139C. Best thing about that IC is that the datasheet is available and it contains information about EEPROM's content. By modifying the EEPROM's content, the VC921 (the true RMS -version) can be turned into a 6000 count DMM, with serial output.Here is a partial English datasheet.

In first attachment, called 921ResetAndSerial.jpg, I've marked pull-up resistor and a capacitor that have been connected to main IC's reset pin. To program the onboard 24c02 without desoldering it first, one can short out C8 to reset the IC, which will prevent it from trying to communicate with EEPROM.
After setting bit 1 of the byte in location 0xFA to 1 (ie. changing that byte from 0xCC to 0xCE), serial output can be enabled by long pressing the REL-button. Pad where this serial output will be available has been also marked in that attachment. I have very limited amount of gear and time to test this function, as I won't be home for next week or so. I was able to see that long pressing the REL enables some kind of output on that pad, as LED that I connected to it starts to blink. Verdict: "I guess it works."

Changing from 4000 count to 6000 count needed multiple modifications. Here are addresses and new values (This information can be found on the datasheet that I linked above):
0x10 : 0x70
0x11 : 0x17
0x12 : 0x38
0x13 : 0x18
0x14 : 0x44
0x15 : 0x02
One example benefit of this modification is ability to measure 5V supplies with 1mV resolution. Proof that this works is in second attachment, called 6000count.jpg

While I had the DMM open, I also changed capacitance mode into mV mode (60mV and 600mV ranges). I've posted more information about this kind of modification in the UT210E topic. Third attachmen, 60mV600mV.jpg shows that indeed the capacitance mode has been replaced with mV mode.


I think itsthatidotagain said it well:
I wouldn't actually recommend it as a multimeter, since the construction is incredibly cheap, but if you want something to hack, and are only using it for low voltage experiments, it would make a pretty neat $10 logging DMM.
 
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