Faded Beauty DMM Gets An OLED Makeover

When a fine piece of lab instrumentation crosses your bench, you’ve got to do your best to put it to work. But even in the highest quality devices no component lasts forever, especially vacuum tubes. For some vintage instruments with vacuum fluorescent displays, that means putting up with less-than-perfect digits in order to get that sweet, sweet precision. Or not – you can always reverse engineer the thing and add a spanking new OLED display.

The Hewlett-Packard 34401A digital multimeter that fell into [qu1ck]’s lap was a beauty, but it had clearly seen better days. The display was full of spuriously illuminated dots and segments, making it hard to use the 6.5 digit DMM. After a futile bit of probing to see if a relatively easy driver fix would help, and with a replacement display being made of solid unobtanium, [qu1ck] settled in for the long process of reverse engineering the front panel protocol. As luck would have it, H-P used the SPI protocol to talk to the display, and it wasn’t long before [qu1ck] had a decent prototype working. The final version is much more polished, with a display sized to fit inside the original space occupied by the VFD. The original digits and annunciator icons are recreated, and he added a USB port and the bargraph display show in the clip below.

We think it looks fabulous, and both the firmware and hardware are on Github if you’d like to rescue a similar meter. You may want to check our guide to buying old test gear first, though, to get the most bang for your buck.

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LEDs Give HP 3457A DDM’s LCD Display The Boot

Have you ever been so frustrated with a digital display that you wanted to rip the whole thing out and create a better one? That is exactly what [xi] did. Replacing their constantly used HP 3457A multimeter’s LCD display with a brighter LED one was a necessary project — and a stress reducing one at that.

While this digital multimeter is well-known for its reliability, its standard display is rather lacking. In fact, there are several mods already out there that simply add a backlight. However, as [xi] notes, LCD screens always have a certain angle where they still don’t quite show properly. So this hack reverses the LCD’s protocol and details the process of creating new LED display.

The issue of dim displays that comes with traditional digital multimeters is not a new one. One solution to this that we have seen before is a hack where someone decided to add a backlight onto their cheap multimeter. [Ken Kaarvik] got around the dimness altogether by giving his multimeter a wireless remote display of his choosing. It is interesting to see the different solutions that are made to the same nuisance. The first item on the agenda of [xi]’s hack was to successfully analyze the HP LCD protocol. With the aid of an ATmega32, the digits were decoded throughout the transmission frames.

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Ask Hackaday: What Tools Do You Reach For First?

Let’s face it, in your workshop there are convenient tools, and there are quality tools, but so often they aren’t both. Think back to the tools you reach for first. Very often for me, speed and convenience win out. I don’t want to look too hard for that drill or saw, and want them to work as expected when I reach for them. At the same time, there are some tools that simply must be stored away, and can’t perch on my workbench forever or sit on a shelf.

It really is a balancing act sometimes. I don’t have a sure fire formula for when to break out the expensive tools, and what jobs are easy with the less expensive. I’ll lay out some of my most-often utilized tools in my arsenal, then I want to hear from you on your own faves.

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Fluke 12E+ Multimeter Hacking Hertz So Good

It kind of hurts watching somebody torturing a brand new Fluke multimeter with a soldering iron, even if it’s for the sake of science. In order to find out if his Fluke 12E+ multimeter, a feature rich device with a price point of $75 that has been bought from one of the usual sources, is actually a genuine Fluke, [AvE] did exactly that – and discovered some extra features.

fluke_12E_CDuring a teardown of the multimeter, which involved comparing the melting point of the meter’s rubber case with other Fluke meters, [Ave] did finally make the case for the authenticity of the meter. However, after [AvE] put his genuine purchase back together, the dial was misaligned, and it took another disassembly to fix the issue. Luckily, [AvE] cultivates an attentive audience, and some commenters noticed that there were some hidden button pads on the PCB. They also spotted a little “C”, which lit up on the LCD for a short moment during the misalignment issue.

The comments led to [AvE] disassembling the meter a third time to see if any hidden features could be unlocked. And yes, they can. In addition to the dial position for temperature measurement, [AvE] found that one of the hidden button contacts would enable frequency and duty cycle measurement. Well, that was just too easy, so [AvE] went on checking if the hidden features had received their EOL calibration by hooking the meter up to a waveform generator. Apparently, it reads the set frequency to the last digit.

The 12E+ is kind of a new species of Fluke multimeter: On the one side, it has most of the functionality you would normally expect from a “multi”-multimeter – such as measuring both AC and DC voltage, current, capacitance and resistance – and on the other side it costs less than a hundred dollars. This is made possible by the magic of international marketing, and Fluke seems to distribute this crippleware product exclusively in the Chinese market. Therefore, you can’t buy it in the US or Europe, at least not easily. A close relative of the 12E+ which should be a bit easier to obtain is the Fluke 15B+; the meter we saw earlier today when [Sprite_TM] hacked it to share measurements via WiFi. The 15B+ seems to be identical to the 12E+ in appearance and features, although it’s unknown if the two are hackable in the same ways.

Thanks to [jacubillo] for the tip!

Need A Nano-Ammeter? You Already Have One!

[Dannyelectronics] sometimes needs to measure tiny currents. Really tiny, like leakage currents through a capacitor. He’s built a few setups to make the measurements, but he also knew he’d sometimes want to take readings when he didn’t have his custom gear available. So he decided to see what he could do with an ordinary digital meter.

dmm-nano-ammeterAs you might expect, a common digital meter’s current scales aren’t usually up to measuring nano- or pico-amps. [Danny’s] approach was not to use the ammeter scale. Instead, he measures the voltage developed across the input impedance of the meter (which is usually very high, like one megaohm). If you know the input characteristics of the meter (or can calibrate against a known source), you can convert the voltage to a current.

For example, on a Fluke 115 meter, [Danny] found that he could read up to 60nA with a resolution of 0.01nA. A Viktor 81D could resolve down to 2.5pA–a minuscule current indeed.

We’ve looked at the difficulties involved in reading small currents before. If tiny currents aren’t your thing, maybe you’d like to try charging an iPhone with 3 KA, instead.

$50 Multimeter Comparison And Teardown

We remember when buying even a modest digital multimeter was a big investment. These days, you can find tool stores giving away cheap meters and if you are willing to spend even a little money, you can buy a meter with tons of features like capacitance, temperature, and other measurements.

Like most things, though, you can pay a little money for a bargain, or you can overpay for a dud. To help you pick, [TechnologyCatalyst] decided to do an extensive video review of 15 different meters in the under $50 price category.

If you are looking for a quick video to watch, you might want to move along. The review is in nine videos ranging from an introduction, to a comparison of build quality, discussion about the displays on each meter, and, of course, the measurement capability of each meter. There’s even a video that shows tear downs so you can see inside the instruments.

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DIY Multimeter, Arduino Sold Seperately

Arduino-based Multimeter

You can’t argue that Arduinos are extremely popular with the maker/hacker community. Some would say that there is certainly no shortage of projects to make using them. [Milen] thought otherwise and felt it was time to create an Arduino-based multimeter.

At the heart of this project  is a common Arduino Uno. The additional parts were kept to a minimum in order to keep down the overall cost and project complexity. The finished product can measure voltage from 0-100v, amperage up to 500mA and resistance between 0-250 kohm. If you need to check for continuity, it can do that too.

All of the parts required to make the multimeter fit on a shield that plugs directly into the Arduino. Banana plugs allow for attaching test leads. The measurement values are displayed on an LCD screen and/or (if connected) to the Arduino IDE Serial Monitor. If only using the serial monitor, the LCD screen can be omitted to save a few bucks.

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