Nanovolt Meter Requires Careful Design For Accuracy’s Sake

Measuring voltages is fairly straightforward most of the time. Simply grab any old cheap multimeter, hook up the probes, and read off the answer. If, however, you need to measure very tiny voltages, the problem gets more complex. [Jaromir-Sukuba] designed a nanovoltmeter specifically to deal with this difficult case.

The nanovoltmeter is exactly what it sounds like: a voltmeter that is sensitive and stable enough to measure and report voltages on the scale of nanovolts. Having a tool that can do this reliably can be very useful when it comes to measuring very small resistances or working with ever-so-slight differential voltages. Continue reading “Nanovolt Meter Requires Careful Design For Accuracy’s Sake”

Heathkit IM-13 VTVM Repair

If you are under a certain age, you might not know the initialism VTVM. It stands for vacuum tube voltmeter. At first glance, you might just think that was shorthand for “old voltmeter” but, in fact, a VTVM filled a vital role in the old days of measuring instruments. [The Radio Mechanic] takes us inside a Heathkit IM-13 that needed some loving, and for its day it was an impressive little instrument.

Today, our meters almost always have a FET front end and probably uses a MOSFET. That means the voltage measurement probes don’t really connect to the meter at all. In a properly working MOSFET, the DC resistance between the gate and the rest of the circuit is practically infinite. It is more likely that a very large resistor (like 10 megaohms) is setting the input impedance because the gate by itself could pick up electrostatic voltage that might destroy the device. A high resistance like that is great when you make measurements because it is very unlikely to disturb the circuit you are trying to measure and it leads to more accurate measurements.

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Homebrew Metrology The CERN Way

We won’t pretend to fully grok everything going on with this open-source 8.5-digit voltmeter that [Marco Reps] built. After all, the design came from the wizards at CERN, the European Organization for Nuclear Research, home to the Large Hadron Collider and other implements of Big Science. But we will admit to finding the level of this build quality absolutely gobsmacking, and totally worth watching the video for.

As [Marco] relates, an upcoming experiment at CERN will demand a large number of precision voltmeters, the expense of which led to a homebrew design that was released on the Open Hardware Repository. “Homebrew” perhaps undersells the build a bit, though. The design calls for a consistent thermal environment for the ADC, so there’s a mezzanine level on the board with an intricately designed Peltier thermal control system, including a custom-machined heat spreader blocker. There’s also a fascinatingly complex PCB dedicated solely to provide a solid ground between the analog input connector — itself a work of electromechanical art — and the chassis ground.

The real gem of this whole build, though, is the vapor-phase reflow soldering technique [Marco] used. Rather than a more-typical infrared process, vapor-phase reflow uses a perfluropolyether (PFPE) solution with a well-defined boiling point. PCBs suspended above a bath of heated PFPE get bathed in inert vapors at a specific temperature. [Marco]’s somewhat janky setup worked almost perfectly — just a few tombstones and bridges to fix. It’s a great technique to keep in mind for that special build.

The last [Marco Reps] video we featured was a teardown of a powerful fiber laser. It’s good to see a metrology build like this one, though, and we have a feeling we’ll be going over the details for a long time.

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Wireless Quad Voltmeter Brings It All Together

If you’re reading Hackaday, you almost certainly have a voltmeter. Matter of fact, we wouldn’t be surprised to hear you had two of them. But what if you needed to monitor four voltage levels at once? Even if you had four meters, getting them all connected and in a convenient enough place where you can see them all at once is no small feat. In that case, it sounds like the multi-channel wireless voltmeter put together by [Alun Morris] is for you.

Built as an exercise in minimalism, this project uses an array of components that most of us already have kicking around the parts bin. For each transmitter you’ll need an ATtiny microcontroller, a nRF24L01+ radio, a small rechargeable battery, and a handful of passive components. On the receiver side, there’s an OLED screen, another nRF radio module, and an Arduino Nano. You could put everything together on scraps of perfboard like [Alun] has, but if you need something a bit more robust for long-term use, this would be a great excuse to create some custom PCBs.

While the hardware itself is pretty simple, [Alun] clearly put a lot of work into the software side. The receiver’s 128 x 32 display is able to show the voltages from four transmitters at once, complete with individual indicators for battery and signal level. When you drill down to a single transmitter, the screen will also display the minimum and maximum values. With the added resolution of the full screen display, you even get a very slick faux LCD font to ogle.

Of course, there are some pretty hard limitations on such a simple system. Each transmitter can only handle positive DC voltages between 0 and 20, and depending on the quality of the components you use and environmental considerations like temperature, the accuracy may drift over time and require recalibration. Still, if you need a way to monitor multiple voltages and potentially even bring that data onto the Internet of Things, this is definitely a project to take a look at.

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Soldering Practice Kit Remains Useful After Completion

Unsatisfied with the standard fare of soldering practice kits that offer little to no purpose once they’re built, [Jim Heaney] decided to take matters into his own hands and design an easy-to-assemble kit for his class that, once put together, becomes the handiest of tools in any maker’s workbench: a functional voltmeter.

At the heart of the kit is a standard Atmega 328P microcontroller. While he could’ve picked something smaller or cheaper, not only does the bulky part make for easier soldering, [Jim] reasons that it’s a chip that’s easy to repurpose should his students want to build something like a breadboard Arduino, for example. The voltmeter has a fixed measurement range from 0 to 100 VDC, the only switches on the board are for powering it on and a hold button, which freezes the value currently being shown in the three-digit, seven-segment display.

Along with selling his kit to other makers and educators, [Jim] also hopes that his project encourages others to design similar soldering kits which favor some sort of function rather than getting binned once there’s solder on all the pads, as well as part variety and documentation. If you’re on the other end of the soldering spectrum, then why not challenge your skills soldering on a time limit?

Voltmeter Clock Looks Great On Display

Voltmeters are cheap, and have a great industrial aesthetic about them. This makes them prime candidates for hackers looking to do a clock build. [Brett Oliver] went down this very road, and built a very stylish timepiece along the way.

[Brett] initially wanted to go with 240-degree voltmeters, however the cost was prohibitive, so settled for the more common 90-degree models. New dials were produced by first sanding down the old dials, repainting in an old-fashioned off-white, and then applying the new graphics with inkjet transfer paper.

The attention to detail continues with the case. [Brett] aimed to build the clock with an old-school lab equipment aesthetic. A large piece of mahogany was crafted into the base.  A clear plastic cover was sourced from eBay, which really makes the piece. Large buttons and toggle switches were chosen to complete the look.

On the electronic side of things, it’s all run by a PIC16F628A, which controls the voltmeters via PWM. Running with a 20MHz crystal, the PIC is not a great timekeeper. Instead, the whole show is synchronized to [Brett]’s master clock we featured a few years back.

Building a clock is a rite of passage for a hacker, and [Brett]’s example goes to show how craftsmanship can really pay off in this pursuit. Video after the break.
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Building A 6.5 Digit Voltmeter From Scratch

After initially working to create a modernized replica of a Czechoslovakian 4-digit Metra M1T242 voltmeter, [Jaromir Sukuba] figured that while he was at it, he might as well create a voltmeter that would be slightly more capable. This led to the design and construction of a brand-new, 6.5 digit voltmeter design, which [Jaromir] has documented over at EEVBlog.

Employing an MSP430FR5994 MCU for the digital board, and an Altera/Intel EPM240T100 CPLD plus ADC on the input side, the design has been undergoing validation for a while now. The current revision uses an OPA140 op-amp in an integrating ADC setup in a multi-slope run-up configuration, but [Jaromir] has plans to replace this input board with another op-amp in a more efficient topology in the future.

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