The Right Circuit Turns Doppler Module Into A Sensor

March 31, 2017 by 22 Comments

Can you buy a working radar module for $12? As it turns out, you can. But can you make it output useful information? According to [Mathieu], the answer is also yes, but only if you ignore the datasheet circuit and build this amplification circuit for your dirt cheap Doppler module.

The module in question is a CDM324 24-GHz board that’s currently listing for $12 on Amazon. It’s the K-band cousin of the X-band HB100 used by [Mathieu] in a project we covered a few years back, but thanks to the shorter wavelength the module is much smaller — just an inch square. [Mathieu] discovered that the new module suffered from the same misleading amplifier circuit in the datasheet. After making some adjustments, a two-stage amp was designed and executed on a board that piggybacks on the module with a 3D-printed bracket.

Frequency output is proportional to the velocity of the detected object; the maximum speed for the sensor is only 14.5 mph (22.7 km/h), so don’t expect to be tracking anything too fast. Nevertheless, this could be a handy sensor, and it’s definitely a solid lesson in design. Still, if your tastes run more toward using this module on the 1.25-cm ham band, have a look at this HB100-based 3-cm band radio.

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Make A PVC Drill Press

March 31, 2017 by 32 Comments

There are two types of people in this world: people who think that PVC is only suitable for plumbing, and people who don’t even know that you can use PVC to carry water. Instructables user [amjohnny] is clearly of the latter school. His PVC Dremel drill press is a bit of an oldie, but it’s still a testament to the pipefitter’s art. And you can watch it in action in the video embedded below.

Things we particularly like about this build include the PVC parallelogram movement, springs around tubes to push the Dremel head back up, and the clever use of a T-fitting and screw plug to hold the press in its lowest position. We wonder how one could add a depth stop to this thing. No matter, we love watching it work.

Anyway, this is just one hack of many that emphasizes the importance of a drill press in basically anyone’s life, as well as the ease of DIY’ing into one. If you’re in the PVC-haters camp, but have some scrap wood and drawer slides or plastic offcuts lying around, you have the makings of a rudimentary press — a welcome tool in the shop.

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Real World RF Filter Design And Construction

March 30, 2017 by 13 Comments

We bet when [devttyS0] made his latest video about RF filter design (YouTube, embedded below), he had the old saying in mind: in theory, there’s no difference between theory and practice, but in practice, there is. He starts out pointing how now modern tools will make designing and simulating any kind of filter easy, but the trick is to actually build it in real life and get the same performance. You can see the video below.

One of the culprits, of course, is we tend to design and simulate with perfect components. Wires have zero resistance, capacitance, and inductance. Inductors and capacitance have no parasitic elements in our rosy design world. Even the values of components will vary from their ideal values and may change over time.

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Hack Your Own Lisp Language Using… Well… Anything

March 30, 2017 by 22 Comments

Lisp is one of those interesting computer languages that you either love or hate. But it has certainly stood the test of time. Of all the ancient languages that are still in practical use, only FORTRAN is older, and only by one year. If you ever wanted to learn Lisp, [Kanaka] has an interesting approach: Study how to build your own Lisp in your favorite language.

What if your favorite language is something obscure? [Kanaka’s] GitHub page has no fewer than 64 different implementations of Mal (Make a Lisp), each in a different language. Unsurprisingly, C and Python are on the list. However, so is Forth and Go and Awk. Not strange enough for you? How about Make? Yes, Make, like you use to build programs. Bash, Postscript, and even VHDL have entries, although–surprisingly–no Verilog; we don’t know why.

Each implementation of Mal is separated into eleven incremental, self-contained, and testable steps that demonstrate core concepts of Lisp. The last step can actually run a copy of itself–typical for a mind-bending language like Lisp. There is a guide to help you navigate through the process in the language of your choice. The suggestion is to not look at the code in the repository until after you’ve written it yourself. You can see [Kanaka] (also known as [Joel Martin]) giving a recent talk about the Mal process in the videos below.

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Robot Arm From Recyclables

March 30, 2017 by 7 Comments

A robot assistant would make the lives of many much easier. Luckily, it’s possible to make one of your own with few fancy materials. The [circuito.io] team demonstrates this by building a robot arm out of recyclables!

With the exception of the electronics — an Arduino, a trio of servo motors, and a joystick — the arm is made almost completely out of salvaged recyclables: scrap wood, a plastic bottle, bits of plastic string and a spring. Oh, and — demonstrating yet another use for those multi-talented tubers — a potato acts as a counterweight.

Instead of using screws or glue, these hackers used string made from a plastic bottle as a form of heat shrink wrap to bind the parts of the arm together. The gripper has only one pivoting claw for greater strength, and the spring snaps it open once released. Behold: your tea-bag dunking assistant.

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Creepy Tracking At The House Of Mouse

March 30, 2017 by 70 Comments

If it’s been a few years since you’ve been to Disney World, you’re in for a surprise on your next visit. It seems the Happiest Place on Earth has become the Trackiest Place on Earth thanks to the Disney MagicBand, a multipurpose wristband that acts as your pass to all the Disney magic.

[Adam] recently returned from a Disney vacation and brought back his MagicBand, which quickly went under the knife for a peek at the magic inside. It turns out the technology is fairly mundane — a couple of flex PCBs with trace antennas and the usual trappings of an RFID transponder. But there’s also another antenna and a chip identified in a separate teardown as an NRF24LE1 2.4 GHz transceiver and microcontroller. The whole thing is powered by a coin cell, meaning the band isn’t just being interrogated by RFID – it’s actively transmitting and receiving.

What exactly it’s doing isn’t clear; Disney was characteristically cagey about specifics when [Adam] looked into the details, saying only that the bands “provide information that helps us improve the overall experience in our parks”. If you put aside the privacy concerns, it’s truly mind-boggling to think about the systems that must be in place to track thousands of these MagicBands around the enormous Disney property. And we can’t help but wonder if some of Disney R&D’s EM-Sense technology is at work in these wearables.

Thanks to [JohnU] for the tip.

Hackaday Prize Entry: A CNC Mill Without The C

March 30, 2017 by 17 Comments

It’s a staple of home CNC construction, the 3D mill built on the bench from available parts. Be the on a tubular, plywood, or extruded aluminum frame, we’ve seen an astonishing array of mills of varying levels of capability.

The norm for such a mill is to have a computer controlling it. Give it a CAD file, perform the software magic, press button, receive finished object (Or so the theory goes). It’s a surprise then to see a mill in which the input doesn’t come from a CAD file, instead all control is done by hand through the medium of a joystick. [Mark Miller]’s 3D printed freeform carving machine is a joystick-controlled mill with a rotary tool on an arm facing a rotatable bed, and it can perform impressive feats of carving in expanded foam.

You might ask why on earth you should make a machine such as this one when you could simply pick up a rotary tool in your hand and start carving. And you’d be right, from that perspective there’s an air of glorious uselessness to the machine. But to take that view misses the point entirely, it’s a clever build and rather a neat idea. We notice he’s not put up the files yet for other people to have a go, if someone else fancies making CNC software work with it then we’re sure that would be possible.

There is a video showing the basic movements the mill is capable of, which we’ve put below the break. Best to say, though, it’s one on which to enable YouTube’s double speed option.

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