Calibration, Good Old Calibration

August 14, 2025 by Al Williams 6 Comments

Do you calibrate your digital meters? Most of us don’t have the gear to do a proper calibration, but [Mike Wyatt] shares his simple way to calibrate his DMMs using a precision resistor coupled with a thermistor. The idea is to use a standard dual banana plug along with a 3D-printed housing to hold the simple electronics.

The calibration element is a precision resistor. But the assembly includes a 1% thermistor. In addition to the banana plugs, there are test points to access the resistor and another pair for the thermistor.

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Dentist Tool Hardware Inspires Non-Slip Probe Tips

June 26, 2023 by Donald Papp 19 Comments

Cross-pollination between different industries can yield interesting innovations, and a few years ago [John Wiltrout] developed some non-slip meter probe adapters. He recently used our tips line to share some details that you won’t see elsewhere, letting us know how the idea came to be.

It started with [John] being frustrated by issues that will sound familiar: probes did not always want to stay in place, and had a tendency to skid around at the slightest provocation. This behavior gets only more frustrating as boards and components get smaller. John was also frustrated by the general inability to reliably probe through barriers like solder masking, oxidation, and conformal treatments on circuit boards. Continue reading “Dentist Tool Hardware Inspires Non-Slip Probe Tips” →

Fluke DMM Hack Adds One Digit To Model Number

February 7, 2022 by Chris Lott 28 Comments

Among his many interests, [Dave Jones] likes test and measurement equipment. He recently posted a few videos on his EEVblog exploring the reasons why Fluke voltmeters are so expensive. In the process, he stumbled upon an interesting hack for the Fluke 77.

The Fluke 77 was introduced in 1983, and is an average responding meter in the AC modes. This model has become a de-facto standard for use in maintenance depots and labs for equipment which has very long lifespans — think military and industrial gear, for example. Many test procedures and training materials have been designed around the use of the the Fluke 77. The cost to change them when a new and better meter comes along is usually so prohibitive they might as well be cast in stone — or at least hammered into 20 pound fanfold paper by a WordStar-driven daisy-wheel printer. But for those unburdened by such legacy requirements, Fluke has the 17x series of True RMS reading meters from since the beginning of this century. These meters bear a strong visual resemblance to their siblings in the 7x family and are substantially interchangeable but for their AC measurement methods. Continue reading “Fluke DMM Hack Adds One Digit To Model Number” →

Faded Beauty DMM Gets An OLED Makeover

August 29, 2018 by Dan Maloney 24 Comments

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

November 15, 2017 by Lauren Faris 18 Comments

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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Need A Nano-Ammeter? You Already Have One!

February 1, 2016 by Al Williams 23 Comments

[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.

As 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.

Say Watt? A Talking Multimeter?

March 23, 2014 by Marsh 41 Comments

talkingMultimeter

After a request from one of his friends, [Mastro Gippo] managed to put together a talking multimeter to be used by blind persons working in electronics. He wanted a feature-rich meter that had serial output, and recalling this Hackaday article from a few years back led him to find a DT-4000ZC on eBay, which has serial output on a 3.5mm jack. (Though, he actually recommends this knockoff version which comes with excellent documentation).

It turns out there aren’t many talking meter options available other than this expensive one and a couple of discontinued alternatives. [Mastro Gippo] needed to start from scratch with the voice synthesizer, which proved to be as easy as recording a bunch of numbers and packing them onto an SD card to be read by an Arduino running the SimpleSDAudio library.

He found a small, battery-powered external speaker used for rocking out with music on cell phones and hooked it up to the build, stuffing all the electronics into an aluminum case. Stick around after the jump for a quick video of the finished product!

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