Dead Simple Time-Domain Reflectometry With Just A Battery And An Oscilloscope

December 14, 2020 by Dan Maloney 29 Comments

“Time-domain reflectometry” sure sounds like something that needs racks of expensive equipment to accomplish. In reality, TDR is just measuring the time between injecting a pulse into a cable and receiving its echo, either from the other end of the cable or from some fault or defect along the way. It’s a useful technique, and as [Allen Wolke (W2AEW)] shows us, it can be accomplished with little more than a battery, a resistor, and an oscilloscope. And a little math, of course.

There are, of course, dedicated time-domain reflectometers, but all of them are really just elaborations of the basic principles [W2AEW] demonstrates with his simple setup. The oscilloscope is set up with a tee connector on one channel; one side of the tee is connected to the cable under test, while the shield conductor of the other side is connected to the negative terminal of a 9V battery. A resistor connected to the center conductor is used to complete the circuit, which sends a brief pulse down the test cable. The scope is set up to capture the outgoing pulse as well as the return pulse, allowing the time between the two to be measured. Some simple math gives the length of the cable, the distance to a fault, or with a little rearrangement, the velocity factor of the cable.

The video below shows the simple method at work on coax and Cat 5e Ethernet cable. It even worked on a roll of zip cable, which was a little surprising. If this technique is too simple, you can always elaborate a bit and roll your own TDR tester. Googly eyes optional, of course, but recommended.

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Railroad Rail Transformed Into Blacksmith’s Anvil With The Simplest Of Tools

December 14, 2020 by Dan Maloney 42 Comments

One of the biggest challenges facing the aspiring blacksmith is procuring the tools of the trade. And that means tackling the unenviable task of finding a decent anvil. Sure, one can buy an ASO — anvil-shaped object — at Harbor Freight, but a real anvil is much harder to come by. So perhaps the beginner smith’s first build should be this railroad rail to anvil conversion.

Repurposing sections of rail into anvils is hardly a new game, but [The Other Finnish Guy]’s build shows us just how little is needed in terms of specialized tooling to pull this off. Other than a file, the bulk of the work is done by angle grinders, which are used to cut off the curved crown of the rail section, cut the shape of the heel, and rough out the horn. Removing that much metal will not be a walk in the park, so patience — and a steady supply of cutting wheels and sanding discs — is surely required. But with time and skill, the anvil hidden inside the rail can be revealed and put to use.

We have questions about the final result, like its lack of a hardy hole and the fact that the face isn’t hardened. We wonder if some kind of induction heating could be used to solve the latter problem, or if perhaps a hardened plate could be welded into the top to make a composite anvil. Still, any anvil is better than no anvil. More on the anatomy and physiology of these tools can be had in [Jenny List]’s article on anvils, and her whole excellent series on blacksmithing is highly recommended. [Jenny]’s not the only smith we have on staff, though — [Bil Herd] has been known to smite a bit too.

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Building A Tiny Finger Plane For Detailed Work

December 14, 2020 by Lewin Day 16 Comments

A plane is a tool familiar to all woodworkers, used to shape a workpiece by hand by shaving away material. Regular planes are two-handed tools available at all good hardware stores. For finer work, a finger plane can be useful, though harder to find. Thankfully, [Daniel] put together a video showing how to make your own.

[Daniel]’s build relies on stabilized wood, useful for its density and consistent quality, though other woods work too. A 6″ pen blank is enough to make a pair of matching finger planes. A block and two side panels are cut out from the material, with attention paid to making sure everything remains square for easy assembly. The parts are glued together with a block set at the desired cutting angle for the plane. With the assembly then tidied up on the bandsaw and sander, [Daniel] installs the cutting blade. This can be made from a larger standard plane blade, or a cutdown chisel can be pressed into service. The blade is held in place with a wooden wedge beneath a metal pin. The pin itself is crafted from an old drill bit, cut down to size.

It’s a useful tool for doing fine plane work, for which a full-size tool would be ungainly. We can imagine it proving particularly useful in producing accurate scale models in smaller sizes. If you’re big into woodworking, consider giving your tools a good sharpen on the cheap, too. Video after the break.

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Can You Use An Easy-Bake Oven For Reflow Soldering?

December 13, 2020 by Kristina Panos 12 Comments

The answer is yes, yes you can. As long as you have one made after about 2011, at least. In the video after the break, [Blitz City DIY] takes us briefly through the history of the venerable Easy-Bake Oven and into the future by reflow soldering a handful of small blinky boards with it.

You’re right, these things once used special light bulbs to cook pint-sized foods, but now they are legit ovens with heating elements that reach 350°F and a little above. The only trouble is that there’s no temperature controller, so you have to use low-temperature solder paste and an oven thermometer to know when to pull the little tray out. Other than that, it looked like smooth sailing.

If you’re only doing a board every once in a while, $40 for a reflow oven isn’t too shabby. And yeah, as with all ovens, once you’ve reflowed a board in it, don’t use it for food.

If you’d rather build an oven, high-powered light bulbs will still do the trick.

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Putting The Finishing Touches On A 60W Laser

December 11, 2020 by Tom Nardi 26 Comments

At this point if you’re even remotely interested in home laser cutters, you know about the K40. These imported machines are very impressive considering they only cost around $400 USD, but naturally, quite a few corners had to be cut to get the price down. If you’re looking for something with a bit more punch and much higher build quality, a new breed of 60 watt lasers have started popping up on the usual import sites for around $2,000 USD.

While these more expensive machines are certainly much higher quality than the K40, [Jeremy Cook] found there was still plenty of room for improvement. For example, the machine didn’t have any switch cut off the laser when somebody opens the lid. While we don’t doubt some readers will consider this more of a feature than a bug, it’s hard to believe that a tool that costs this much wouldn’t at least offer such a thing as an option.

[Jeremy] also decided to add his own ammeter so he could see how much power the laser is drawing. While not strictly required for day to day operation, it turns out that the controller in many of these machines has a tendency to push the laser tubes beyond their design limits on the higher power settings. With the spec sheet for your tube and a permanent in-line ammeter, you can verify you aren’t unwittingly shortening the life of your new cutter.

Even if you ignore the modifications [Jeremy] makes in his video, it’s still a very illuminating look at what it takes to get one of these lasers ready for operation. Not only do you have to get the thing out of its shipping crate safely, but you need to come up with some way to deal with the fumes produced and get the water cooling system hooked up. It’s a decent amount of work, but the end results certainly look impressive.

While the K40 is still probably the better bet for new players, it’s good to see that there are some viable upgrades for anyone who’s outgrown their entry level machine but isn’t in a position to spend the money on an Epilog.

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Easy Frequency Counter Looks Good, Reads To 6.5 MHz

December 10, 2020 by Al Williams 12 Comments

We were struck by how attractive [mircemk’s] Arduino-based frequency counter looks. It also is a reasonably simple build. It can count up to 6.5 MHz which isn’t that much, but there’s a lot you can do even with that limitation.

The LED display is decidedly retro. Inside a very modern Arduino Nano does most of the work. There is a simple shaping circuit to improve the response to irregular-shaped input waveforms. We’d have probably used a single op-amp as a zero-crossing detector. Admittedly, that’s a bit more complex, but not much more and it should give better results.

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Wireless Quad Voltmeter Brings It All Together

December 10, 2020 by Tom Nardi 4 Comments

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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