An Introduction To Differential I²C

March 31, 2017 by 45 Comments

A few weeks back, we talked about the no-nos of running I²C over long wires. For prototyping? Yes! But for a bulletproof production environment, this practice just won’t make the cut. This month I plucked my favorite solution from the bunch and gave it a spin. Specifically, I have put together a differential I²C (DI²C) setup with the PCA9615 to talk to a string of Bosch IMUs. Behold: an IMU Noodle is born! Grab yourself a cup of coffee and join me as I arm you with the nuts and bolts of DI²C so that you too can run I²C over long cables like a boss.

What’s so Schnazzy about Differential Signals?

There’s a host of ways to make I²C’s communication lines more noise resistant. From all of the choices we covered, I picked differential signals. They’re simple, fairly standardized, and just too elegant to ignore. Let’s take a moment for a brief “differential-signals-101” lecture. Hopefully, you’re already caffeinated! Continue reading “An Introduction To Differential I²C” →

Gaming Beyond Retropie

March 31, 2017 by 28 Comments

Looking for something a bit more from your Raspberry Pi? Tired of the usual console and arcade games? Eltech’s Exagear Desktop is a virtual machine that runs on your Raspberry Pi and allows you to run x86 games. [Dmitry]’s done a write-up about running more modern games on your Raspberry Pi.

Up until now, the Pi has been a great platform for retro gaming. By running MAME or EmulationStation, you can play classic arcade games as well as the great console games you played as a kid. Exagear Desktop goes one further, allowing you to use Wine to play more modern PC games on your Raspberry Pi 3.

The Pi 3 is still a bit underpowered for bleeding edge games, but is powerful enough that it can play some of the PC games from a few years ago. [Dmitry]’s example shows how to get Arcanum, Disciples II, and Fallout running on the Raspberry Pi. In the second part of the write-up, [Dmitry] shows you how to get Heroes of Might and Magic 3, Sid Meier’s Alpha Centauri, and Caesar 3 installed and running as well.

Obviously they will always lag behind today’s gaming machines, but the power now available in a computer the size of a credit card is pretty impressive. It’s nice to have a tool that allows one to play more than just the console games from years gone by — this opens up a whole range of great PC games to add to our library. Maybe it’s time to fabricate that new PC game controller.  Or, if the Raspberry Pi seems like too much power, you could consider playing retro games on an Arduino.

Linux-Fu: Applications On The Web

March 31, 2017 by 38 Comments

Did you know you can run remote Linux GUI programs in a browser with HTML5 support? It’s even secure because you can use SSH tunneling and that little trick means you don’t even need to open additional ports. If this sounds like gibberish, read on, it’s actually pretty easy to get up and running.

I recently was a guest on a Houston-based podcast, and the hosts asked me if the best thing about writing for Hackaday was getting to work with the other Hackaday staff. I told them that was really good, but what I like best was interacting with people (well, most people) in the comments. That sometimes you’d post an article and someone would bring a topic up in comments that would really knock your socks off. This is how I wound up with this nearly ideal remote access solution, that requires nothing on the remote side but a web browser.

A while back I posted about keeping programs running after log off on a Linux box. The post was mostly about non-GUI programs but you could use NX or VNC to handle it. In the comments, someone mentioned how unhappy they’d been with recent copies of NX and another commenter called [Screen for X11] posted about a tool called xpra.

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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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