Review and tear-down of the Ruideng UM34C USB Tester

In this video, I take the UM34C USB Tester apart as far as possible, go over its functions and verify its claimed accuracy specs for measuring voltage, current and capacity.
In summary (starts at 42 minutes into the video)
The UM34C does the basic job of measuring voltage and current on the USB bus really well as long as you don’t have to go below 4V and I definitely recommend it for that purpose. The results are accurate, the display is easy to read and if you have the Bluetooth version and the app, the spreadsheet recording capability can be very useful. Capacity and energy measurements work well as long as you don’t use the threshold. Don’t buy it for the cable impedance facility unless you have a suitable load.
I found instructions in English here: (updated link 30-Oct-2020)
www.mediafire.c...
My video on the electronic load is here:
• Adding an enclosure to...

[@wa9kzy326]

Wow! That is the way a product report should be done; detailed and clearly explained, recored both video and audio. Very well written script. Thank you.

[@particlecloud]

Love the thoroughness and level of detail in this!

[@markusfister970]

Very thoroughly tested! It's a pity you didn't check the functionality with a USB3 host and device. You might have been surprised! I wanted to use it like that and connected it to a USB3 port an a computer and a load resistor. Only this type of load resistor had a USB3 connector. The current shown by the UM34C was far too low! BUT: If you connect to a USB2 load resistor instead, the measured current is correct. Connect the UM34C to a USB2 host, but using a USB3 load resistor, the current is correct, too! Only if both, the host and the device, are USB3 the current measured is much too low! I disassembled the UM34C just like you did and took some measurements. And I discovered what I would call a design flaw. The UM34C has the current shunt resistor placed into the ground connection between the female USB3 connector and the three input connectors. On USB2 connectors there is only one ground pin, but on USB3 connectors, there is a second ground pin between the two superspeed data line pairs, called "ground drain". This signal (on pin 7) is usually connected to the same ground line as pin 4 in hosts and devices. But in the UM34C, pin 7 of the male USB connector is routed directly to pin 7 on the female USB3 connector on the other side and not connected to ground. This means, that as soon as you connect a USB3 host (which connects pin 7 and pin 4 to ground) to the UM34C and then plug in a USB3 device (which also connects pin 7 and pin 4 to ground), the UM34C cannot measure the current accurately, because there is effectively a second ground connection in parallel to the shunt resistor in the UM34C between host and device, and the curent flowing through this second connection cannot be measured! IMHO the correct way of designing the UM34C would hava been to connect the ground drain pin on both USB3 type A connectors to pin 4 and not route it to the other connector independently, so there is only one ground connection between input and output (via the shunt resistor). edit: spelling

[@markusfister970]

@@vegane_athee Here's what I did: If you remove the upper plastic shield (on the display side), you can access the solder joints of the USB3 plug. The USB3 socket's solder joints are under the display and you would have to remove it to reach them. I just cut the PCB trace of the middle pin on the USB3 plug. The one right in the middle of the row of contacts is the GND drain signal. By cutting this, current can't flow through this ground connection circumventing the current measurement anymore. Of course this is no ideal solution. Ideally you would connect this GND drain to GND on both the USB3 plug and USB3 socket, but as this is not possible on the socket side without removing the display, I didn't do it. GND drain is usually connected to GND in the USB host as well as in a USB device, so the drain wire in the USB cables should still be connected to GND. As I said this is by no means a perfect solution to the problem, but works for me. I did not check to see what happens if you use the USB-C connector instead of the USB3 plug. Don't know if GND drain is connected the same way.

[@Sysshad]

Very good video, i like the technical bits! Do note that if you are transmitting with the bluetooth transciever it will draw much more current then shwo in about 20:00

[@TheHWcave]

Good point. I should have tested that when BT was active. Thanks for pointing it out.

[@Sysshad]

@@TheHWcave no problem. I can understand why you left it out and only used the idle current :) It's difficult to measure dynamic current, need a good multimeter, mostly it's best to do it with an oscilloscope and by measuring a series resistant voltage. Then converting its mean voltage to amperes. But that's if you want to be really precise though. Also have to pick a very small series resistance so it won't affect the load, maybe it the size of 10, 100 milliohms.

[@I967]

A very well done review. It helped me to understand the cable resistance test feature, the manual for my UT25 wasn't clear enough. Basically a USB tester of this style shows volts and amps and the other features are mostly gimmickery.

[@keithking1985]

Wow!! I think that was the best review of a product of ever seen👏👏 you covered everything 🙏👌

[@mixtube797]

excellent review👍 are you half French and half German 😉

[@bird104G]

This is what I was looking for thanks

[@rdtech9153]

Thank you very much for your review and video, from the video, you should be professional, but there is something I need to see 1, for your current , your way is wrong, you need to use at least 6 bit meter to compare , our meter have 5 bit , resolution is 0.001A, your load resolution is 0.01A, how could you compare our meter , you should find 0.0001a mulitimeter to compare 2, for cable resistance , our way is voltage difference to count a about resistance , not accuracy, it need to compare more 2 cable resistance , and we need to set 1A for load, not 0.5A thank you again

[@Petertronic]

Excellent testing and explanations, this is very useful. I think this tester is amazing for the price. I also have a BM235, nice meter :)

[@paulpearce172]

So so much better than other reviews, which mostly seem to consist of "Look how many digits are displayed" and "look how many screens there are". Please keep making these detailed reviews that are a fix for my "want more in-depth tech. knowledge" habit.

[@benedictterry5958]

I guess Im asking the wrong place but does anybody know of a trick to get back into an instagram account..? I was dumb lost my password. I would appreciate any tips you can give me!

[@dariusaarav2886]

@Benedict Terry instablaster =)

[@benedictterry5958]

@Darius Aarav Thanks for your reply. I got to the site on google and I'm waiting for the hacking stuff atm. Takes a while so I will reply here later with my results.

[@benedictterry5958]

@Darius Aarav It worked and I actually got access to my account again. Im so happy:D Thanks so much, you saved my ass !

[@dariusaarav2886]

@Benedict Terry No problem xD

[@yahnsolo]

20:28 In fact CPU keeps runinng at this point but the display shuts off. You still can see the 8mAh from the CPU going on. it really stops when 3.3 LDO output comes around 2.65v, and it will tend to reset when voltage comes back too quick. I've modified my UM34C to use measuring capacity of cells. I hookup 3.35v from an external source, and feed it directly to the electrolytic capacitor on the LDO output. This way, using 3.35v, i make sure the STM Cpu will push it current from my external source, not from the internal LDO at 3.33 or 3.34. Thus I wont be including its own consumption on my capacity logs, AND, most important, I'll be able to measure Voltages as low as 0 volts. So basically, feeding it externally and separately from it's USB bus allows me to test capacity of my LiPo's (as low as 2.8 or 2.5v no issue). Just my 2 cents :)

[@TheHWcave]

that's a great modification and makes the UM34 so much more useful.

[@yahnsolo]

@@TheHWcave yess and for it’s price it’s really worth it ;)

[@rdtech9153]

now we change bluetooth board to support IOS app

[@joaosousa3640]

Hi Rd Tech, how the end customer knows which units support IOS app?

[@rdtech9153]

@@joaosousa3640 hello, UM24C is the only cummunication USB tester which doesn't support IOS app, others can support both IOS and Android system

[@BuildingCenter]

Rd Tech I visited Hangzhou a while back. Slick little town. Spent too much time walking around Xihu. Favorite city in China.

[@rdtech9153]

@@BuildingCenter yes, and there are many delicious food you can try haha

[@hallo_matthew7627]

Very detailed video! Thank you! Keep up doing videos!

[@gobyg-major2057]

It’s not really pointless...the temperature thing just tells u if it’ll get hot.....

[@TheHWcave]

Yes, that is true, although I must admit I totally ignore it.

[@BuildingCenter]

First video by this guy that I’ve seen. Incredibly detailed, focused. Great documentation. Additional resources in the description box. Masterful presentation, overall. I benefit from YT allowing faster playback, and his excellent English. Thanks for smashing this teardown, TheHWCave.

[@TheHWcave]

Hi BuildingCenter, many thanks, glad you liked the video.

[@wei48221]

Thank you for the effort in making this informative video.

[@JesseGyger]

Excellent informational review. Keep it up!

[@jipede]

Excellent work

[@lens1736]

Very comprehensive review and usable review. Thank you

[@downundergarage6968]

Best review on the web by far.. well done.

[@2ftpmarco]

thanks for making this !

[@ru15151]

Superb. The product's not bad either.

[@groveh1]

Great review!! Thanks!!!

[@Skewbee]

Found IOS app, UM_METER, in App Store. No need to side load.

[@rdtech9153]

for our new version, it should IOS app please check your version

[@javierpallalorden]

You mentioned that the dropout voltage = 3.96V, that is NOT correct, only the screen is switched off, the processor keeps running!

[@TheHWcave]

Yes, you are correct. I noticed that when I tested other models later (we live and we learn). Its not much lower though, 3V is when my UM34C stops and reboots when the voltage is increased again.

[@NoferTrunions]

I there no control on how the X-axis is handled when viewing the graph? I would have liked the default to be all the data, it would start with he 1st point and just keep packing more and more points into the chart (the display would always show the entire XL file). It would be nice to see a complete 1 hour curve of a battery discharge test.

[@TheHWcave]

Yes, I agree that the automatic plotting scaling is not all that useful. That is why I always ignore the graph and instead export the automatically recorded data for use in a spreadsheet to plot it the way I want.

[@richardfabish607]

Nice review. I ended up buying one. One question - where did you find the document displayed in your video - the technical one about 6 minutes into the video?

[@TheHWcave]

You mean the data sheet on the processor? Just Google STM8S005c6. The second result is a PDF from www.st.com

[@davidforbes513]

I noticed at 2:43 of your video, BTW an excellent video review/teardown, that the printed descriptions on the back cover do not match the various components on the PCB. Specifically, your cover shows an ON/OFF switch and a USB-C OUT designation that at 2:49 of your video, where you remove the back cover to reveal the PCB, it is apparent that there is no ON/OFF switch nor a USB-C OUT connector on your PCB. Just curious about this anomaly?

[@TheHWcave]

You are correct that the UM34 does not have a USB Type C out connector. The UM25 has one at this position. Not sure why that is and which device came first in the evolution. There is certainly room for one. The switch is actually there but on the Bluetooth module attached to the cover. When assembled it hovers right above the 0.01 Ohm shunt. You can see it later when I show the Bluetooth board.

[@davidforbes513]

@@TheHWcave Thanks for the quick response... I did'nt think to look at the bluetooth board for the switch but, in retrospect, it makes total sense since the switch turns the bluetooth on/off. I, too, don't know about the evolution of the two testers you mentioned... just thought it weird that it the UM34C tester has a UM25 rear cover on it! Again, thanks for an outstanding video!!

[@vidasvv]

EXCELLENT video !!! Just got mine yesterday but am unable to get the Bluetooth to work. 73 N8AUM

[@22smudger]

I bought one of these based on the fact it has USB type-c input and a range of 4-24 volts, hoping I would be able to check charging of my iPad Pro which charges from PD 19 -ish volts on a type-c cable, but I can’t get the meter to register anything other than normal USB voltage of around 5 volts. I now realise the type-c input has limited connections and is only for testing cables, but even using a type-c to type-a adapter to the standard input port, the meter still only registers 5 volts, and then using a type-a to type-c adapter connected from the meter output to the iPad, does not trigger charging. Is this meter actually capable of monitoring the charge to an iPad Pro; are my adapters hard wired to force 5 volts using resisters across the data + & - pins; or have I got s duff meter?

[@22smudger]

Apologies - I meant 9v charging for the iPad.

[@TheHWcave]

@@22smudger It depends. If the charger and the iPAD support older protocols that only use the standard D+ and D- lines then it should do at least say Quick-Charge 2 or 3. On the USB-C you may have to flip the plug because the D+ and D- signals are not mirrored in the plug so orientation of the USB-C plug matters for these modes. The more advanced charging modes (USB-C PD) won't work when this tester is put into the circuit because it does not carry the signals that are needed for that. It may work if you get a USB-A (standard USB) to USB-C cable and put that between the tester and your Ipad (but not between the tester and the charger). The reason for that is that these cables contain a resistor in the USB-C plug that tells the device how much current it can draw. Most cables of that sort cheekily use a resistor value that enables a lot more current than the puny 0.5A they are supposed to enable by the standard.

[@fredt4977]

Ace review best by a mile. :)

[@joaosousa3640]

What a great review! I want to order two units but I’m not sure about the IOS compatibility and need some clarification from RD Tech

[@sequri]

Works well with iOS (UM Meter app) - at least it has done in the past. Still working with iOS 13.5.1, though the app could do with updating (it takes quite a while to initialize for one thing). I expect the app will stop working at some point, with future iOS versions (unless updated, which I think is unlikely imho), but I have older versions of iOS available anyway, so not a problem, per se.

[@joaosousa3640]

sequri thanks! I’ve ordered and in fact they work with IOS 12 and 13

[@zagreb-boris]

excellent review!!!

[@danielfavelatentori4046]

Is UM34C more/less/same accurate as UM25C?

[@TheHWcave]

Very timely question. I am working on a review and teardown of the UM25 at the moment. Needs a few more days but the initial answer is yes.

[@danielfavelatentori4046]

TheHWcave thank you for your great reviews. Initial answer is yes 34C is more accurate?

[@TheHWcave]

Daniel, many thanks... I realise I should have been more specific, "yes" wasn't a good answer to your question. Yes, the UM25 / UM25c is more accurate than the UM34C. and has better resolution. Unfortunately my video on this will take a bit longer as expected as I need to do some business travel.. Probably closer to the end of Oct. now

[@gobyg-major2057]

36:00 4.54 volts, not 5.54 volts.....

[@TheHWcave]

Oops, thanks for pointing it out. I'd love to fix it but KZbin no longer allows amendments and re-editing the video offline and resubmitting will cause all its history/comments to be lost. Since its just me stating the wrong value but the calculation shown on the screen shows the correct value, I decided to leave it.

[@gobyg-major2057]

Np

[@craigduncan8666]

I just received mine on Saturday but the mediafire link to the English instructions is down - any chance you could re-upload it please?

[@TheHWcave]

I don't have any connection to mediafire or Ruideng but a quick google search finds other locations with possibly even better translated instructions, for example: jucetize.weebly.com/uploads/3/7/2/0/37200949/um34_c__usb_tester_meter__instruction___android_app_instruction-_2_in_1_-__2018.6.13_.pdf

[@craigduncan8666]

@@TheHWcave thank you sir!

[@broderp]

I'm very sure you have TONS of great info for us technical people, but damn I got less than 6 minutes in and couldn't take any more. Could you be any slower and more boring? You are the college professor that had all his students sleeping and or skipping class because it was SO boring! I'll have to watch this video in 5 minute sections so I can get get thru it.

[@sheadjohn]

is there a way to add a battery so that it stays on?

[@dr.kishorkumar256]

Yes..An excellent review.

[@norme1850]

Do you have the link to download the Bluetooth app for the UD18? I just purchased one of these from Amazon and the bar code only goes to a Chinese gaming website and not the app website.

[@TheHWcave]

Unfortunately no. I don't have one of these testers or links to an app.

[@norme1850]

Thanks. I figured out that E_Test app will work but you have to have GPS location on on your phone for it to work. Not sure why you would need the GPS on for it to work.

[@TheHWcave]

@@norme1850 Again, I dont have a UD18 myself, but my guess is that the app wants your location because the company that makes the UD18 wants it, for whatever purpose (if only for tracking where most of their customers are located). You are correct, I can't see why the USB tester itself would need your location for.

[@baz-jc4qt]

they have a new 1 the TC66C i think you like it, and a video on it would be great😁

[@TheHWcave]

Thanks for the tip and you are right. It would make a great "beware - snake oil" video. I'll looked the specs up and they are ridiculous. Lots of digits on the display but the stated accuracy in no way justifies them. Current in 10uA resolution sounds great until you see its accuracy is only +-1% +20 digits. A true current of exactly 1 Amp could read as 1.01020 and be (just) in spec. Same issue for volts. I would stay clear of this. If it ends in a bargain sale, I might get it and do a fun video on it, but at the moment it is way too expensive for what it offers. That said, I did pick up a UT25C in a bargain sale and it has 1mV for volts and 100uA for current (so both just one digit less than the TC66C). I have not had time to test it yet but expect similar accuracy issues and might make a video on it in the next couple of weeks.

[@rdtech9153]

@@TheHWcave for your TC66C, it is just max error range , for more accuracy meter , it is normal for accuracy, if you find one to compare . and we don't think it is ridiculous. 6 digit is very had for 5 digit , you should know that for UT25C , it is just copy for our UM25C, and his accuracy is absolutely of UM25C accuacy, because we have our own device to calibarate, but UT25 did not have, he just copy our program . if you don't believe, i can provide UM25c to compare as you want to evaluate some thing, you should make a research thank you

[@Vimes.]

I was a little concerned towards the end of the video when you noted the Android App version "phones home" - is that a real cause for concern...? Also, unless I'm missing something really obvious here what actual advantage does this UM34C offer over the UM25C...? I can imagine similar app concerns apply for the UM25C as for the other model..? A shame that the app has to be downloaded from Mediafire and not within the Android app store. Thanks for the informative review.

[@TheHWcave]

Hi Morgan, Advantages: The UM34 is (usually) a little less expensive than the UM25. If you don't need the extra digit resolution and can live with 4 Amps instead of 5 Amps max current, then it is still a very good tester. Phoning home was maybe the wrong expression. It loads a Chinese advertising page on startup, but as far as I know it did not send any of your stuff. Sideloading. That was needed when I made the video some time ago. Nowadays , just go to the app store and search for RuiDeng or UM34. I believe the same RuiDeng app can now handle (almost) all their USB testers and USB enabled power supplies. I tested it just now. I had some initial problems but after turning on Bluetooth myself and pairing with the UM34C (pin 1234) the RuiDeng app worked fine.

[@Vimes.]

@@TheHWcave Thanks for the reply. The phoning home comment did concern me a little. I have now received my UM25C and from the little that I have tested it I'm impressed. My TC66C is still shipping from Ali express, with that one I believe that you can trigger various protocols that a charger may support, like QC for testing.

[@TheHWcave]

@@Vimes. Thanks for the update.. Hope you like the TC66C. I am still looking for an excuse to get it... (I have way too many USB testers) but a good USB-C tester would be nice.

[@Vimes.]

@@TheHWcave The UM25C can be justified, nice upgrade over my Muker J7 usb tester, and will be used. The TC66C is perhaps something of an indulgence. Point taken tho, we all need certain excuses for what we buy. I'll sometimes accept "new and shiny" if nothing else fits. lol

[@noakeswalker]

I now have the non-bluetooth version of this meter as a result of watching your review. It will get used for easily measuring currents that usb devices draw, and for measuring mAh into various non-usb diy rechargeable torches I've built over the years - need to make some adaptors for that though.....as you suggest here, I have turned off the 'record' threshold, well, I think it's actually 10mA because you can't dial in 0, but that's fine. It's a shame that only button display colours can be changed, but none of the actual measurement fields can - red on a dark background is quite hard to read sometimes ! Also, the exposed pcbs at the sides are a bit vulnerable as you said, so it will live in its storage box mostly...Otherwise, no complaints, it's very good. Thanks. Dave

[@mortyjones732]

Lots of clones now flooding the market. Do you have a link for genuine Ruideng ?

[@TheHWcave]

Ruideng has an official shop on Alibaba: rdtech.en.alibaba.com/ I have never used it, so I have no advise to give how well that works. I recently bought a TC66C from Banggood which is genuine (I think), but then I also got a fake UM25C from Banggood, so YMMV.

[@TheHWcave]

Actually, I think that link above is only for resellers (unless you want to buy qty 10 of each). This one: rdtech.aliexpress.com/store/923042 may be for buying single items. Again, I have not used it. No idea how well buying rdtech from aliexpress works.

[@lexpee]

The instructions link is not working, website not fount.

[@TheHWcave]

Well, that video (and the link) are 2 years old, so things like websites can change.. I googled it and a new link that works (today) is www.mediafire.com/folder/5c877rc21tp1p/UM34 It has English and Portuguese Instruction manuals in PDF format.

[@frankgensler3806]

I got all information I wanted to know - thank you very much :-)

[@CircleOfSnakes]

This also works with UM24C windows software. The UM24C is USB 2.0, but it has the same resolution. You said the Bluetooth pin pairing was 1234, so i tried it, and it paired in Windows 10. I then installed the UM24C windows software and it communicates with the device perfectly. It also connects with UM25C Windows software, but with the resolution being higher on that device, the digits are off and other functions like brightness level and auto screen off do not work.

[@TheHWcave]

Glad it works for you. I must admit I only used the Android app, and never tried their Windows software because my home PC is not Windows. Since I did this video, RDtech did upgrade their Android software (now in Google playstore) but it seems to be pretty similar to the earlier version. One thing that is different is that it now tries to automatically open the recorded spreadsheet which IMHO is a bit of a daft thing on Android because it assumes you have apps installed that can do xls files. That may be something that sneaked in from the Windows version.

[@mehmetocak6849]

When I connect to the meter via USB-C port and amp drops down from 1amp to 0.49 amp, why? the usb cable is the fast charging cable I tested it to charge my samsung with fast charger and it works fast confirmed it, but if i use that cable as a bridge in as usb-c to the meter voltage and amp drops. if I directly connect the meter to the charger then I get 1amp, if if i connect it via fast charging enabled usb-c cable it drops by half. how and why I have no clue, anyone knows? becasue what if it is like that naturally what is the purpose of haviing usb-c and usb-micro in?

[@TheHWcave]

This is not a USB-C tester. The USB-C port is basically paralleled to the micro-USB for convenience to save you from getting an adapter cable. But this means that the USB-C only uses the wires of a micro-USB, so there are only the standard 4 wires plus, gnd, and D+/D- supported. The charging voltage & current you get depends whatever the charger and phone have implemented using just these wires. By the looks of it, it degrades to the default "safe" setting of 5V and 0.5A which means it doesn't even see the D+D- lines. One thing you could try is turning the USB-C plugs around. Although for USB-C plug orientation is supposed to not matter, strictly speaking for plugs this is not quite true because D+D- is only implemented on one set of pins and not on the mirror image other half. On a cable with USB-C plugs on both ends you may have to try flipping both ends = 4 possibilities.

[@mehmetocak6849]

@@TheHWcave One end is normal usb and other end is usb-c port, so normal usb goes in to the wall charger and usb-c in to the tester in port, I have tried flipping it and did not make difference. I have tried several cables that charges my phone fast speed(so I know these cables are fast charging cables) but if I use them as an extention cable with usb-C in port on the tester voltage drops slightly and amp drops by half, Therefore, there is no use for USB-C port it is just a gimmick to me. In addition if connect with micro-usb in port it works normal, so usb and micro-usb ports gives full amp, usb-c port gives half amp , tested this with 3 different fast charger and 5 different cables to make sure fault is not on my side. Thank you for your reply

[@elhoucineeddali2839]

there is a difference between displayed output voltage and the set voltage with my DPS5005 module, how can i calibrate it ? same thing with current. thank you

[@TheHWcave]

Can you explain your setup? You are feeding the UM34 from a DPS5005? Do you have a load on the other side of the UM34C and if so what current does it draw? My guess is that the voltage on the UM34C is lower than the DPS5005 because of the voltage drop on the cable between the two. If you use thin cables and high currents, this drop can easily be a volt or more. Best way to confirm if that is the problem for voltage is to have no load on the UM34C. In that case the two displays should be almost identical. On the current, the UM34C uses about 24 mA for itself, so the current on the DSP5005 will always be slightly higher than what's shown on the UM34C display. Does that help?

[@SuperFelipetto]

Thanks !

[@igsaturation]

Great job! Danke.

[@dimensitybg]

I'm Using KWS-MX18 USB tester

[@TheHWcave]

The KWS-MX18 looks like a nice enough tester and that it has a calibration function is great. Some reviews say its not very accurate out of the box (especially the current). What is your experience? Have you calibrated it?

[@dimensitybg]

@@TheHWcave yes I calibrated it

[@dimensitybg]

@@TheHWcave kzbin.info/www/bejne/h2WoYYiogpV6m9k

[@adolforosado]

English instructions attempted to pass me a virus.

[@Alphasmsn]

Please review the latest ruideng TC66C, thank you!

[@TheHWcave]

Looks very interesting. I am considering it.

[@marcamant7258]

Do you think that it could be possible to fit a power source in order to get it independant from the device we want to measure?

[@TheHWcave]

Hi Marc, It certainly wouldn't be easy to do in such a way that everything still works. That said, if you look at my video on USB tester surprises (published 21-Dec-2019) you see that I mention a tester that can do that YZXSTUDIO: ZY1280 but its very expensive and I have no idea how good it is. There may be others out there... The video I mentioned also talks about minimising the error caused by the self-supply of the tester when doing capacity testing of batteries, if that is your concern. Depending on your load you can lower the error to 1% which for casual battery testing and comparisons is good enough in my experience. Of course if you want more accuracy, recording and things like timers or turning off when voltage, capacity or current thresholds are crossed , you can do as I did and build your own DC power monitor, Raspberry Pi zero based, which can do everything a USB tester can measure (and more) and runs of mains (or a power bank). That is a 5 part video series published early last year. Schematics and software can be downloaded freely from my Github page (see video descriptions for the link)

[@marcamant7258]

@@TheHWcave I thank very much of such a compehensive answer. I shall follow your remaks and jump to the various references you have so gratefully shown to me. Nice to read you. A M

[@oskimac]

And the tear down?

[@f14v14n]

Very useful and detailed video! Enjoyed every minute of it. Do you think the circuit can be modified to use an external power supply (a battery) to power the STM microcontroller so it can measure voltages below 4V?

[@TheHWcave]

Hi Flavian, glad you liked it. Modifying the UM34C might be possible but sounds like an awful amount of work and a substantial risk breaking the unit for good. Depending on what you want measure, the UNI-T UT658 USB tester I reviewed a couple of months ago can go down to 3V (but no higher than just below 10V). It is not quite as good as the UM34C but not bad. Another way is to just sacrifice a USB cable by cutting it, allowing you to put a normal multimeter in between the two ends.

[@f14v14n]

Already did the multimeter thingy, but it's quite messy compared to simply plugging a meter in, hence I bought the UM25, which I really don't want to risk breaking. I don't think there are a lot of cases in which I would have measured under 4V anyway. If I'll want the meter to influence the power draw as little as possible, I guess I'll use the Bluetooth with the screen off. Very glad you've shown the power draw in all the cases!

[@MarcoLopesPT]

You can't... But i just found this one (pt.aliexpress.com/item/33046323602.html) that has POWER input, but nothing is said about it on the page... Can't find a review of it. It's seems like a clone of the U2, that has POWER input capability (pt.aliexpress.com/item/33044188328.html)

[@barrygreengrass3379]

Where do you get the app from, what do you mean by the app has to side loaded? I don’t understand. I’ve ordered the UM34C today, I will be a while before I receive it.

[@TheHWcave]

Hi Barry, you can find the link to download the app on the last page of the English instructions (link to that PDF in the description of the video). What I mean with side loaded is that it isn't in the app store. You need to either use the link in the PDF directly on your phone/tablet to download and install it or download it on a PC and then copy the file onto your phone/tablet and install it (click on it). If you have Oreo (8.1) a message pops up to ask if you really want to do that. In Nougat (7) and below you need to go to Settings -> Security-> and enable installation of apps from unknown sources first. Don't forget to disable that afterwards.

[@barrygreengrass3379]

Thanks for the info, when I click on the link from the pdf file it doesn’t say UM34C only UM25C I don’t know what to do.

[@TheHWcave]

You are absolutely correct. I should have made this clearer. I actually forgot that the app is the same for all UM models. Download the "UM Series Android App 3 in 1_V3.0.0 which is what I used.

[@Noobinski]

Thank you for this still great ressource. I bow to the thoroughness of your expedition. Since I want to test cables and comsunptions now and then I purchased such a device and am quite happy with it, based on your helpful insights. Anyway the app now is available in app stores and I wondered if they - just maybe - fixed the problems you stated in the firmware, too. The trickle charge data glitch remains, for the cable resistance measurement I will order an electronic load in the next days. Did that with seemingly stable loads until now, but I do not trust that much. Do you have a suggestion on what USB load generator to buy in 2021? Since your video about that is from 2018... Budget seems to be around 30 Euros regardless of which one you choose...

[@TheHWcave]

The one that I use is still available at Banggood for around 25 euros, they also have some that can handle more watts... and some specifically for USB testing for around 14 euros. The question you have to ask yourself is whether you are more interested in a generic one (like the one I use) or one that is specific for USB and has a USB connector on it. The latter ones are easy if all you do is USB stuff. The other one is far more versatile for all kinds of batteries (including car batteries and measuring 18650s directly) but you need to rig up a USB adapter.

[@Noobinski]

@@TheHWcave Thanks for the quick reply! Just last night I purchased one off of ELV, the only one they got in fact. Came about 18 Euros plus shipping. It is a 35W-USB-load with all USB connectors except mini, which I think I can adapt to anything else that does not supply more power. By applying the respective connectors, yes. If you happen to have the time and nerve to make a vid about checking how good these loads are calibrated with a vanilla multimeter, I would be interested very much, indeed. :D

[@TheHWcave]

It would be interesting to learn about your experience with it. Unfortunately I don't plan to buy a new electronic load, USB or other, at least for now since my current one does all I need. One of the things I would really like to know is how it accounts for the power it needs to operate (electronics + fan) if it takes that power, as I suspect, from the same USB connection that you are measuring? Or does it use external power?

[@Noobinski]

@@TheHWcave ​ Yes, that's the weird part in my opinion, too. Same thing as with the UM34C, it takes the power from the same "line", which it should either leave as untouched as possible or regulate with as little electric interference (in the help-yourself-you're-very-welcome sense) as possible. I did not dare to put it to use yet. But things might change: I happen to give shelter to a Siglent laboratory power supply these days; let's see if that gives me any ideas, especially in combination with the UM34C. Es bleibt spannend! :D

[@TheHWcave]

Indeed, But other than a USB tester, the purpose of the load is to consume power, so in that sense I would not mind if it takes its operating power from the source. If it does it properly its display should show that there is a minimum load current that is always there. More worrisome may be that if the source voltage collapses when applying a decent load current as cheap USB chargers are prone to do. In that case, there is nothing left to power the electronic load and it will shut down. That , in turn, will probably remove the load current, so the charger and the output voltage recovers. It would be interesting to know if yours gives an indication that this has happened (you may not have witnessed it) and stays off. Or, does it automatically resume loading the source, which then collapses again ... rinse and repeat

[@barrygreengrass3379]

Is possible to clear / zero the Accumulated Capacity & Accumulated Energy

[@TheHWcave]

Yes it is. In the first screen (the one that shows current and accumulated data at the same time), a long press on the PREV button clears the accumulated data of the selected group. In the same screen a long press on the NEXT button increments the group number. I glossed over that function because I never use groups. There are 10 groups (0..9) to keep accumulated data for up to 10 devices, or maybe more usefully compare the accumulated data with one from a previous run. There isn't a function to clear all data from all groups at once. You need to do it for each group.

[@barrygreengrass3379]

@@TheHWcave Many thanks.

[@khun1pla]

Nettes Video. Weitermachen bitte

[@stevenv2190]

So, this tool is useless in this scenario - Laptop has USBC, and you want to re-image the laptop. This device will not verify that the USB-C port on the laptop is good and will not fry anything that is inserted into it.

[@TheHWcave]

I am not sure what you are after. Are you concerned for example that a USB-C powered external drive will work? No tester can tell you that. You can check what the voltage is and what current flows but if that is too much or too little for the device connected, the tester has no clue. Also for USB-C I would rather use a more modern special USB-C tester instead of the UM34C which is predominantly for the older USB ports.

[@A6D6E6]

Very thorough explanation. Thanks.