Victor 921 pocket dmm - reviewed by toddfun.com ($11 on ebay) - Page 1
Forum section: electronics / testgear

author: retiredcaps
author_rank: Super Contributor
timestamp: February 20, 2016, 06:53:46 am
content: 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.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: February 20, 2016, 09:06:15 am
content: 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.

author: mos6502
author_rank: Frequent Contributor
timestamp: February 20, 2016, 11:20:21 am
content: 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.

author: hugatry
author_rank: Contributor
timestamp: July 23, 2016, 02:10:42 pm
content: 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" toldin the UT210E -topicthat 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, theVC921 (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 outputcan 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 countneeded multiple modifications. Here are addresses and new values (This information can be found on the datasheet that I linked above):0x10 : 0x700x11 : 0x170x12 : 0x380x13 : 0x180x14 : 0x440x15 : 0x02One example benefit of this modification is ability to measure 5V supplies with 1mV resolution. Proof thatthis worksis in second attachment, called 6000count.jpgWhile 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 modificationin 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:Quote from: itsthatidotagain on June 27, 2016, 04:34:52 pm