The True Cost Of Multimeters

If you are building a home shop, it is common to try to get the cheapest gear you can possibly get. However, professionals often look at TCO or total cost of ownership. Buying a cheap car, for example, can cost more in the long run compared to buying an expensive car that requires less maintenance. Most consumers will nod sagely and think of ink jet printers. That $20 printer with the $80 cartridges might not be such a deal after all. [JohnAudioTech] bought a few cheap multimeters and now has problems with each of them. Maybe that $120 meter isn’t such a bad deal, after all.

The problems he’s seen are the same ones we’ve all seen: noisy selector switches, suspect display readings, and worn off lettering. You can see the whole story in the video below.

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Cordless Drill Sprouts Wings And Takes Flight

Brushless motors and lithium batteries were a revolution for remote control aircraft. No longer would nitro engines rule the roost, as flying became far cheaper and more accessible almost overnight. The same technology has also found its way into power tools, leading to [Peter Sripol] deciding to build a powerdrill into a flying aircraft in this video, embedded below.

An unmodified DeWalt drill is the heart of the build, serving as the propulsion unit of the craft. A servo is used to actuate the drill’s trigger to serve as the throttle. As power drills are geared down significantly compared to a typical hobby brushless motor, it was necessary to use a much larger prop than would be usual. This was custom machined out of wood with the help of [William Osman], and despite some mishaps, came out (mostly) in one piece. The airframe consists of foam wings with poplar spars, and an aluminium extrusion serves as the tail boom. A few 3D printed parts then tie everything together.

Despite the weight of the drill, the hacked-together craft is able to fly quite easily. The large wings and propeller help to make up for the shortcomings of the powertrain. Unfortunately, there wasn’t quite enough surplus lift to carry a payload of smartphones to capture in-flight footage, but overall the project could be considered a resounding success.

We’ve seen [Peter]’s work before, too – sometimes even putting himself in the pilots seat! Video after the break.

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A DIY Bench-Sized Milling Machine

Hanging around the machining community online, you’d be more than familiar with clapped out Bridgeport mills, which are practically a meme at this point. But mills come in all shapes and sizes, from the stout old iron from the days of yore, to smaller, compact builds. [Honus] decided to build the latter, and shared the details of the project.

The aim of [Honus’s] build is to create a small benchtop mill, capable of handling the smaller tasks. The frame of the mill is built out of 80/20 extrusion, with plenty of aluminium plate to go along with it. Igus linear slides handle the X, Y and Z axes. An old brushed Makita drill motor serves as the spindle drive, controlled by an old R/C speed controller hooked up to an Arduino. [Honus] then fabbed up various bits and pieces as neccessary to bring it all together.

The mill is neat and tidy, and looks to do a good job machining aluminium. We imagine it should prove highly useful in [Honus’s] workshop. If you’re contemplating getting yourself some desk-sized tools, perhaps consider an engraver as well! Video after the break.

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The Final Days Of The Fire Lookouts

For more than a century, the United States Forest Service has employed men and women to monitor vast swaths of wilderness from isolated lookout towers. Armed with little more than a pair of binoculars and a map, these lookouts served as an early warning system for combating wildfires. Eventually the towers would be equipped with radios, and later still a cellular or satellite connection to the Internet, but beyond that the job of fire lookout has changed little since the 1900s.

Like the lighthouse keepers of old, there’s a certain romance surrounding the fire lookouts. Sitting alone in their tower, the majority of their time is spent looking at a horizon they’ve memorized over years or even decades, carefully watching for the slightest whiff of smoke. The isolation has been a prison for some, and a paradise for others. Author Jack Kerouac spent the summer of 1956 in a lookout tower on Desolation Peak in Washington state, an experience which he wrote about in several works including Desolation Angels.

But slowly, in a change completely imperceptible to the public, the era of the fire lookouts has been drawing to a close. As technology improves, the idea of perching a human on top of a tall tower for months on end seems increasingly archaic. Many are staunchly opposed to the idea of automation replacing human workers, but in the case of the fire lookouts, it’s difficult to argue against it. Computer vision offers an unwavering eye that can detect even the smallest column of smoke amongst acres of woodland, while drones equipped with GPS can pinpoint its location and make on-site assessments without risk to human life.

At one point, the United States Forest Service operated more than 5,000 permanent fire lookout towers, but today that number has dwindled into the hundreds. As this niche job fades even farther into obscurity, let’s take a look at the fire lookout’s most famous tool, and the modern technology poised to replace it.

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The World’s Smallest Vacuum In An Altoids Tin

There’s been a lot of Altoids tin hacks over the years, but a vacuum cleaner in a tin is something new. In [Toby Bateson]’s first project on Hackaday, he used simple household items to create a functioning vacuum cleaner to use for sucking crumbs out of your keyboard or paper punch holes off your desk.

The vacuum features a retractable suction tube, a low-profile switch, and a bagless waste collection system (the waste is stored and discarded out from the tin itself). A brushed motor and impeller provide the airflow. A scrap of a beer can mounted on the shaft is used for an impeller blade, and two bolts with a thin metal sheet between them are made into a switch (the instructions recommend you finish your drink before using the scrap metal). A sponge is used for filtering the dirt from the motor while a hole is cut out of the top of the tin to provide airflow.

[Bateson] is looking to put his name in the world record book for the world’s smallest vacuum tube, as he recently created an even smaller vacuum in a 1cc tube.

“Oh dear, I’ve spilled something on my desk, whatever am I going to do? Luckily, I have my vacuum cleaner in an Altoids tin…”

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Make Your Own Plasma Cutter

Of all the tools that exist, there aren’t many more futuristic than the plasma cutter, if a modern Star Wars cosplay if your idea of futuristic. That being said, plasma cutters are a powerful tool capable of making neat cuts through practically any material, and there are certainly worst ways to play with high voltage.

Lucky enough, [Plasanator] posted their tutorial for how to make a plasma cutter, showing the steps through which they gathered parts from “old microwaves, stoves, water heaters, air conditioners, car parts, and more” in the hopes of creating a low-budget plasma cutter better than any on YouTube or from a commercial vendor.

The plasma cutter does end up working up quite an arc, with the strength to slice through quarter-inch steel “like a hot knife through butter”.

Its parts list and schematic divide the systems into power control, high current DC, low voltage DC, and high voltage arc start:

  • The power control contains the step down transformer and contactor (allows the DC components to come on line)
  • The high current DC contains the bridge rectifier, large capacitors, and reed switch (used as a current sensor to allow the high voltage arc to fire right when the current starts to travel to the head, shutting down the high voltage arc system when it’s no longer necessary)
  • The low voltage DC contains the power switch, auto relays, 12V transformer, 120V terminal blocks, and a terminal strip
  • The high voltage arc start contains the microwave capacitor and a car ignition coil

At the cutting end, 13A is used to cut through quarter-inch steel. Considering the considerably high voltage cutter this is, a 20 A line breaker is needed for safety.

Once the project is in a more refined state, [Plasanator] plans on hiding components like the massive capacitors and transformer behind a metal or plastic enclosure, rather than have them exposed. This is mainly for safety reasons, although having the parts exposed is evocative of a steampunk aesthetic.

In several past designs, stove coils were used as current resistors and a Chevy control module as the high voltage arc start. The schematic may have become more refined with each build, but [Plasanator]’s desire to use whatever components were available certainly has not disappeared.

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The Cutest Oscilloscope Ever Made

If you thought your handheld digital oscilloscope was the most transportable of your signal analyzing tools, then you’re in for a surprise. This oscilloscope made by [Mark Omo] measures only one square inch, with the majority of the space taken up by the OLED screen.

It folds out into an easier instrument to hold, and admittedly does require external inputs, so it’s not exactly a standalone tool. The oscilloscope runs on a PIC32MZ EF processor, achieving 20Msps and 1MHz of bandwidth. The former interleaves the processor’s internal ADCs in order to achieve its speed.

For the analog front-end the signals first enter a 1M ohm terminator that divide the signals by 10x in order to measure them outside the rails. They then get passed through a pair of diodes connected to the rails, clamping the voltage to prevent damage. The divider centers the incoming AC signal around 1.65V, halfway between AGND and +3.3V. As a further safety feature, a larger 909k Ohm resistor sits between the signals and the diodes in order to prevent a large current from passing through the diode in the event of a large voltage entering the system.

The next component is a variable gain stage, providing either 10x, 5x, or 1x gain corresponding to 1x, 0.5x, and 0.1x system gains. For the subsystem, a TLV3541 op-amp and ADG633 tripe SPDT analog switch are used to provide a power bandwidth around the system response due to driving concerns. Notably, the resistance of the switch is non-negligible, potentially varying with voltage. Luckily, the screen used in the oscilloscope needs 12V, so supplying 12V to the mux results in a lower voltage and thus a flatter response.

The ADC module, PIC32MZ1024EFH064, is a 12-bit successive approximation ADC. One advantage of his particular ADC is that extra bits of resolution only take constant time, so speed and accuracy can be traded off. The conversion starts with a sample and hold sequence, using stored voltage on the capacitor to calculate the voltage.

Several ADCs are used in parallel to sample at the same time, resulting in the interleaving improving the sample rate. Since there are 120 Megabits per second of data coming from the ADC module, the Direct Memory Access (DMA) peripheral on the PIC32MZ allows for the writing of the data directly onto the memory of the microcontroller without involving the processor.

The firmware is currently available on GitHub and the schematics are published on the project page.

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