Handheld Multimeter Converted For Bench Top Use

A few years ago [Mechatrommer] got one of the low-cost Aneng Q1 multimeters and has¬†converted it into a bench top meter. He first tried and failed to do an LCD modification and set it aside. It remained in a storage box until he needed another meter to repair his rubidium frequency standard. Finding that off-the-shelf bench multimeters were literally off-the-shelf — they were too deep for his bench — he decided to take matters into his own hands.

He dug out the dismantled an Aneng Q1 and undertook a more drastic modification than before, slicing the multimeter into three pieces and mounting each piece in a new enclosure. The power-draining back-lit display of the Q1, problematic in a battery-powered handheld meter, isn’t an issue in a bench top design. [Mechatrommer] replaced the battery pack with a mains powered supply. Next he reconnected all the signals which had been interrupted by the bandsaw, and now the meter lives again.

The resulting meter is pleasing enough (ignore the sideways input jacks) and looks like a typical piece of home-brew test gear. The enclosure has a lot of empty space, which he uses to stow test leads and sandwiches (we saw a similar storage compartment in [Dave Jones]’s recent teardown of a portable Fluke 37 multimeter). Kudos to [Mechatrommer] for coming up with this unusual conversion project.

We’ve written about the differences between these low-cost and more professional multimeters before if you want to learn more.

Thanks to [Adrian] for the tip.

Ode To An AVO 8 Multimeter

I’m moving, and in the process of packing all of my belongings into storage boxes to disappear into a darkened room for the next year. Perhaps I could become one of those digital nomads I hear so much about and post my Hackaday stories from a sun-kissed beach while goldfish shoals nibble at my toes. But here in a slightly damp British autumn, box after box of a lifetime’s immersion in tech needs sorting and directing. Why on earth did I hang on to three Philips N1500 VCR system video cassette recorders from the early 1970s! (Don’t worry, those have found a good home.)

Say Hello To An Old Friend Of Mine

Instantly recognisable, the AVO 8
Instantly recognisable, the AVO 8

As I was packing up my bench, I happened upon a multimeter. I have quite a few multimeters and this isn’t the first time I’ve written about these indispensable instruments, but this one’s a little special.

It’s a treasure from my youth, that most venerable of British test equipment: the AVO 8. This was the ubiquitous multimeter to be found in all manner of electrical and electronic workshops across most of the 20th century, and remains to this day one of the highest quality examples of its type.

It’s a relatively huge Bakelite box about 190mm x 170mm x 100mm in size, and it is instantly recognisable¬† by its dual rotary selector switches and the window for viewing the needle, which forms a characteristic circular arc kidney shape.

The earliest ancestors of my meter appeared in the 1920s, and the first model 8 in the early 1950s. Mine is a Mk III that a penciled date on the inside of its meter movement tells me was made in November 1965 and which I bought reconditioned from Stewart of Reading in about 1991, but manufacture continued until the last Mk VIII rolled off the production line in 2008. It’s to my shame that my AVO is a bit dusty and that maybe I haven’t used it much of late, but as I picked it up all the memories of using it to fix dead TV sets and set up optimistic experiments in radio came flooding back. If there’s one instrument that connects me to the youthful would-be electronic engineer that I once was, then here it is. Continue reading “Ode To An AVO 8 Multimeter”

In Praise Of The DT830, The Phenomenal Instrument You Probably Don’t Recognise For What It Is

If we had to make a guess at the single piece of electronic bench equipment owned by the highest proportion of Hackaday readers, it would not be a budget oscilloscope from Rigol, nor would it be a popular portable soldering iron like the TS100. Instead we’re guessing that it’s a multimeter, and not even the most accomplished one.

The DT830 is a genericised Chinese-manufactured 3.5 digit digital multimeter that can be had for an astonishingly low price. Less than a decent hamburger gets you an instantly recognisable plastic case with a chunky rotary range selector switch, and maybe a socket for some kind of transistor or component tester. Make sure that there is a 9 volt battery installed, plug in the pair of test leads, and you’re in business for almost any day-to-day electrical or electronic measurement. They’ve been available in one form or another for decades and have been the subject of innumerable give-aways and loss-leader offers, so it’s a reasonsble guess that you’ll have one somewhere. I have three as far as I know, they make great on-the-go instruments and have proved themselves surprisingly reliable for what they are. Continue reading “In Praise Of The DT830, The Phenomenal Instrument You Probably Don’t Recognise For What It Is”

E-Textile Tools Get The Multimeter Hookup

[Irene Posch] has done some incredible work with knitted, crocheted, and fabric circuits — check out the crocheted ALUs and embroidered computer for starters. Now, it seems [Irene] is building up a how-to catalog of e-textile tools that can be easily connected to a multimeter.

So far, this toolbox includes a seam ripper and a crochet hook. The concept is similar for both — print out a handle and connect the tool to a banana jack that can then be connected to a multimeter. The crochet hook is simple: just print out the handle, jam the hook in one end, and stick a mini banana jack in the other end. They’re designed to butt up against each other and make a connection without wires.

Building the ripper takes a bit more effort. There’s another printed handle involved, but you must first free the seam ripper from its stock plastic handle and solder a wire to it. Then twist the other end of the wire around a banana jack and and put that in the other end of the handle.

It’s great to see a little bit insight into the troubleshooting tools of e-textiles, especially because they are all-around fiddly. It all starts with a circuit, so why not do your prototyping with a thread-friendly breadboard?

Play A Game Of Multimeter

There are many different single board computers that are general purpose, but there’s another breed targeted at specific applications. One such is the Clockworkpi, a handheld Game Boy-style games console, which may be aimed at gamers but has just as much ability to do all the usual SBC stuff. It’s something [UncannyFlanigan] has demonstrated, by turning the Clockworkpi into a multimeter. And it’s not just a simple digital multimeter either, it’s one that sports graphing as well as instantaneous readings.

At its heart is an Arduino board that supplies the analogue to digital conversion, with opto-couplers for isolation between the two boards. A simple three-way switch selects voltage, current, and resistance ranges, and the ClockworkPi interface is written in Python. We can see that this could easily be extended using the power of the Arduino to deliver more functionality, for which all the code is handily available in a GitHub repository. It’s not a perfect multimeter yet because it lacks adequate input protection, but it shows a lot of promise.

If you’re intrigued by this project then maybe you’ll be pleased to know that it’s not the first home made multimeter we’ve featured.

Hackaday Podcast 079: Wobble Sphere, Pixelflut, Skeeter Traps, And Tracing Apps

Hackaday editors Mike Szczys and Elliot Williams gaze upon the most eye-popping projects from the past week. Who would have known that springy doorstops could be so artistic? Speaking of art, what happens if you give everyone on the network the chance to collectively paint using pixels? There as better way to catch a rat, and a dubious way to lure mosquitoes. We scratch our heads at sending code to the arctic, and Elliot takes a deep look at the contact tracing apps developed and in use throughout Europe.

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (~65 MB)

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Continue reading “Hackaday Podcast 079: Wobble Sphere, Pixelflut, Skeeter Traps, And Tracing Apps”

A DIY 6.5-Digit Multimeter Is A Lesson In Clever Circuitry

A multimeter is an easy prospect, right? Back in the day you could make one fairly easily with a decent panel meter and a set of precision resistors, and now a digital one can be had for throwaway prices from China.

But what if instead of a cheap-and-cheerful bench instrument your needs extend to a high-precision device, a really good multimeter? It’s a path [jaromir.sukuba] has trodden with his 6.5 digit multimeter project, and along the way he’s offered us a fascinating window into their design that should be of interest to any electronic engineer even if they never intend to build a multimeter.

The range selection network of switches and resistors, microcontroller, and seven-segment displays are universal to a multimeter design, meaning that there is nothing too special about them in a high-precision instrument except that here he’s using an FPGA for timing.

Where the meat lies in this project is in the ADC and its associated voltage reference, and for that he takes a surprising turn. Instead of taking an off-the-shelf ADC part from one of the usual manufacturers, he’s created his ADC from scratch using op-amps, and to understand why that is the case he takes us on a journey into the world of dual-slope integrating ADCs. These circuits are very well explained in a 1989 HP journal article (PDF, page 8), and are a clever design that measures the time taken to charge and discharge a capacitor from the voltage to be measured and compares it to the same time from the reference voltage.

The beauty of it comes out in the HP article, that the mathematics of the charge/discharge cycle cancel out any effects of the analogue component values, allowing the much higher precision of the reference and the clock timing to dictate that of the reading. We look forward to seeing more of this project.

It’s surprising how few home-made multimeters we have on these pages, perhaps because of those cheap ones. Of the few we’ve had, perhaps this state-based Nixie one is most unusual.