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Forum Index : Microcontroller and PC projects : Digital multimeter for $1.74...
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9630 |
Purely out of interest, I bought a couple of these. Less then two bucks a piece  , but they work OK, surprisingly. Comes with el-cheap-o leads and printed instruction sheet, inside a bubble-bag.I would NOT use these things for any high-voltage probing, but for low-voltage stuff, they would seem to be ideal for throwing in the glove-box of your car, or keeping them around almost as a disposable meter - use it till it craps out or the battery goes flat, then bin it. Looking at its guts(photos below), I can see that the PCB trace spacing is not really up to HV spec, so stay away from the 200v and 500v(eek!) ranges, but everything else LV should be fine. I'd trust them up to around 50v I think. They read very accurately on voltage, and current is within a few mA on the 200mA scale - very useable for two bucks!!!  I did tempt fate - carefully - by jamming the probes into a 230v wall-outlet, and switching on. Not touching the leads or the meter, but it did correctly read the AC outlet voltage, so they seem to be accurate enough despite being so incredibly cheap. They even have a piezo inside for continuity measurements, and they only beep when the resistance is less then about 20 Ohms, which is good. Many a cheap meter will beep so long as there is a circuit between the probes, even a high-resistance one. They are small - fit inside your hand, but the LCD display is big so they are easy to read. Dimensions are 184 x 103 x 25mm/7.24 x 4.06 x 0.98in.     Smoke makes things work. When the smoke gets out, it stops! |
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| Glen0 Regular Member  Joined: 12/10/2014 Location: New ZealandPosts: 95 |
The battery probably costs a lot more than the meter. I hope the probe leads have to be in the current measuring configuration to be able to use the 1.5v and 9v battery testing functions. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9630 |
Just looked at that, and yes - you have to have the red lead in the current hole, then you touch the probes to the battery. With my test 9v battery, I got a reading of 24, which equates to a good battery under a simple load-test according to the very basic manual. Smoke makes things work. When the smoke gets out, it stops! |
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| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 10379 |
That looks terrifying. It has no input protections (zero, nothing, nadda, zilch) and would be a risk to life if used with mains voltages or on a valve amp etc. Best place for it is the garbage so no-one ever mistakenly uses it for high voltage |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8043 |
That's by no means the most horrible cheap meter I've seen. I suspect it'll handle 100V easily (and regularly) as the tracks aren't all that bad IMHO. Well, they aren't if the PCB material and solder mask are reasonable. The leads on these things are always horrid and should usually be binned immediately. The complete lack of fusing will lead to a short working life, methinks, and automatically precludes all use on mains circuits. I've always been a fan of cheap digital multimeters as they are almost always remarkably accurate and can be left monitoring supply voltages and things instead of tying up one of your better quality instruments. The continuity function on this one seems to be good. Does it show continuity through a forward-biased diode? Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2446 |
ideally there should be NO current ranges, as this then eliminates a major source of smoke-escape and the need for fusing. and NO hFE/transistor check, as that 8-pin socket exposes a dangerous connection to the internals. then with just a tiny bit of sensible design, what remains could be rolled into something simple and safe for the average 'home handyman'. one of my favourite multimeters (albeit neither cheap nor obtainable) is the fluke 12b:  cheers, rob :-) Edited 2022-11-11 22:22 by robert.rozee |
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Martin H. Guru Joined: 04/06/2022 Location: GermanyPosts: 1270 |
It's great, if you need a fixed voltage indicator etc. 'no comment |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8043 |
You pays your money, you takes your choice, Rob. :) I fully agree, these things are dangerous to those who don't know the problems. (Actually, they are dangerous anyway if you use them in a lot of situations.) The difficulty is, where do you draw the line? Should it be illegal, for example, to sell any multimeter without fused and shrouded test probes insulated to 1000V just in case someone uses one in a distribution board? I love the Flukes, but you very likely pay more for a high speed fuse for one than you pay for this meter. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| pwillard Guru Joined: 07/06/2022 Location: United StatesPosts: 313 |
Not much better or worse than this one that they often give out for free. Harbor Freight  |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9630 |
Yes, but it does not beep. Forward reading is about 180 on the display, so above the threshold for the piezo to sound so it would seem. But you get a reading on forward, and none on reverse, so it does work. Smoke makes things work. When the smoke gets out, it stops! |
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Rickard5 Guru Joined: 31/03/2022 Location: United StatesPosts: 463 |
I'm gonna order a few and leave them laying out and hide my good meters, so by the idea of path of least resistance, the Cheep meters will grow legs before my good meters will. I may be Vulgar, but , while I'm poor, I'm Industrious, Honest, and trustworthy! I Know my Place |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8043 |
I'd be tempted to modify a cheap meter by soldering a high speed fuse in the COM line if at all possible to marginally improve the safety. At the very least put some paint on the high voltage ranges to remind you never to use them. These meters appear to have no fault protection whatsoever and are obviously manufactured to the Chinese "Disposable People" safety standards. These things may even set fire to the battery if you put them on a voltage input while set to a resistance range. They are fine *in their place* but never let someone who doesn't understand the niceties of multimeter safety anywhere near them. To find out how good they are connect the 200mA range directly onto a car battery. The chances are that it won't work a second time. :) Having said all that, I'm quite willing to be proved wrong. There are clever ways to protect against the wrong inputs now, in fact you can get meters that have no range switch and sort themselves out for most things. However, I doubt if the cheap meters will be using this level of technology. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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retepsnikrep Senior Member  Joined: 31/12/2007 Location: United KingdomPosts: 134 |
For a very cheap isolated voltmeter stack they can be quite useful. I've used the harbour freight ones in multiples of ten to monitor a 20V batter tap on a 200v pack. Each one only sees 20V. Gen1 Honda Insights. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2446 |
remove the 250/500v AC and DC ranges, mark the 200v ranges as "50v max", and provide something direct at the input terminals that trips out at 100v and opens an internal (user replaceable) fuse. also get rid of the 200mV range at the same time - that way you ensure that all voltage ranges have a 9M ohm series resistor. drop the current ranges, hFE, battery check ranges. move the ohms ranges onto the third (A) socket with some suitable input protection. then you can sell this as a 'DSE hobby projects' meter for LOW VOLTAGE use only. note: i'm not suggesting anyone do this with any of the current offerings; making modifications to an existing meter (like adding fuses  ) can lead down a path as equally perilous as blindly using a $2 meter as-sold on high energy circuits.a good read i reference (ad nauseam) is this unfortunate story: https://www.ecmweb.com/safety/arc-flash/article/20898038/the-case-of-the-deadly-arc-flash obviously, none of us would ever land up in this situation, but others less cautious could well do (and indeed have). cheers, rob :-) Edited 2022-11-12 23:07 by robert.rozee |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8043 |
An excellent article, Rob. Now try to find a hobby meter with your specifications. At a price that's sensible - which probably rules out everything sold for the educational market. :( Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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