I like to take things apart. Sometimes they work when I'm done. I've been a member of NYC Resistor since 2010 and you can see more of my projects at


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Sep 122013

Octoscroller temporary installation

Hexascroller has been a central fixture at NYCR for the past few years, with a few ups and downs. It’s replacement, Octoscroller, improves on our classic message alert polygon by having two more sides and two more colors of LEDs.

The userspace application renders images into a shared memory frame buffer, or in this case receives UDP packets containing video images from the Disorient Pyramid transmitter. The PWM algorithm can do between eight and sixteen levels of brightness for each color, producing approximately 12-bit color.

See it in person at MakerFaire in NYC this year and read on for details of how to wire up a driver for the panels, as well as a walkthrough of some of the PRU code.
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 Posted by at 9:41 pm
Sep 052013

Party at the Disorient Pyramid

This year the Disorient Camp at Burning Man built a 7m tall pyramid with over half a kilometer of LED strips. Several artists developed patterns for the panels, including Disorient founder Leo Villareal and Jacob Joaquin from Fresno Idea Works. Every night there was a party in front of the pyramid, with bicycles blocking the entire Esplanade.

The pyramid was visible from just about everywhere on the playa and served as a great beacon for finding the camp after a long night out. Read more for the technical details of how it was constructed and links to all the source code.
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 Posted by at 11:07 pm

Oscilloscope class

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Aug 042013

Diagnosing EL wire with a DSO Nano v3

One of the most powerful tools in debugging circuits is the oscilloscope — it allows you to visualize your analog and digital signals at millisecond or microsecond time scales. This 18 August class at NYC Resistor will teach you basic operation of a handheld oscilloscope: topics include how to setup different time and voltage scales, how to configure the trigger modes to capture fleeting signals and how to use the cursors to measure various qualities of the signals. We’ll also show how to use the ‘scope to trace a signal through a circuit to identify some common problems.

Multimeter amperage measurement

The other most valuable tool in your electrical test equipment toolbox is a multimeter for measuring the instantaneous values of three important electrical measurements: voltage, amperage and resistance. This class covers all three of these as well as the very important “beep mode” to check for electrical connectivity.

Get your tickets here! The class fee includes both a compact multimeter and a DSO Nano v3, an Open Hardware design that is a great getting started oscilloscope. With these in your toolbox you’ll be able to diagnose all manners of circuit issues.

 Posted by at 3:12 pm


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Jul 272013

LEDscape test

Are you building a giant LED display for your hackerspace or Burning Man and need a way to control multiple kilometers of LED strips? Are you tired of running massive USB hubs of Teensys for each row? Then you might be interested in my LEDscape code for the BeagleBone Black to drive up to 500 meters of WS2811 RGB LED strips at 30fps.

On the Teensy 3, Paul’s OctoWS2811 makes very clever use of three DMA engines to generate the bit-train for the WS2811 LED strips, but only supports up to eight strips. Beth’s FadeCandy improves on Paul’s work and has a great frame rate with beautiful interpolation (and a custom USB protocol to pump pixels fast enough to keep up with the frame rate), but the temporal dithering and expanded colorspace features run into frame rate and memory limitations at strips beyond 64 pixels.

The BeagleBone Black has far more memory than the embedded AVRs (512MB versus 16KB) and the AM335x ARM Cortex-A8 has a killer feature: two built in PRU (“Programmable Realtime Units”). These are embedded real-time microcontrollers built into the ARM core with full DMA to main memory and control over all of the IO pins. This afternoon I hacked up a quick proof of concept in PRU assembly that use one of the units to drive 32 of the WS2811 strips at full speed with zero CPU load and easy double-buffering of the image. The best parts of writing for the ARM instead of the AVR is that there aren’t any issues with running out of memory for image processing and there is built-in ethernet for OSC or other visualization libraries.
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 Posted by at 11:39 pm

Future Crew

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Jun 212013

Last month we introduced Future Crew, and at the 2013 Interactive Show we finally unveiled the fully mostly operational game stations. There were five stations in the final design, and in keeping with the show’s “Digital Archaeology” theme, each was built from repurposed ancient hardware. The brains of each console was a Raspberry Pi (to connect to the network and draw OpenGL graphics) and some number of Teensy microcontrollers to interface with the real world. Of course, the source is available for you to build your own Future Crew stations!

Future Crew Game

A discarded video edit console and RF TV became the Timeline controller. Since the Pi can turn the composite video on-and-off, one of the modes glitches out the TV occasionally with real static! This one had some of the more imaginative tasks like “disable all blinking buttons” in addition to the normal tasks like “advance the timeline!”.

Future Crew Game

A rackmount data acquisition analog-digital converter and three NTSC TVs became the Blender control unit and Technobabble patch panel. The labels were printed on our large format plotter and then the BNC holes were cut on the laser cutter. The teensy++ firmware can handle arbitrary cross connects and even multi-way connections. This was one of the harder stations to play — there are eight switches, twenty verbs and twenty nouns. We ended up disabling all the verbs except “MODULATE” since it was much too difficult to find the right ones. As a todo item we plan to ramp up the difficulty as the game goes on.

Future Crew Game

A 1930′s Model 15 Teletype and some random video switcher served as the slowest output console. It’s amazing that the teletype functioned nearly perfectly for the entire eight hour show — perhaps the fresh quart of oil during the previous servicing helped keep it working. The source for this console is one of the simpler ones — it just prints to a file descriptor to write to the teletype.

Future Crew Game

One of the hardest consoles was made from a toy piano. Even with the song book, playing “Row Row Row Your Boat” under duress is not easy.

Dial James Bond!

And a last minute entry was a rotary phone. Quick! Get the President on the line! This time the handset just had a recorded loop, but future games will incorporate text to speech.

We have a whole list of things to fix and improvements to make before Makerfaire 2013. Stop by NYCR to play it during Craft Night on Thursdays and give us your suggestions!

 Posted by at 11:54 am

Space Rocks

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Jun 082013

Space Rocks on the oscillograph

Cathode ray oscillographs weren’t just used for reading tweets in the 1940′s, they were also used as vector displays for serious astronomical simulations and training systems like “Space Rocks”. You can play it at the 2013 NYC Resistor Interactive Show!

While the Delta-V of the simulator space craft was optimistic for its era, the basic acceleration, velocity and position model is reasonably accurate. If the ship passes too closely to one of the space rocks, it is destroyed and the simulation restarts. Once the ship runs out of fuel (measured in hexadecimal in the upper left corner since the CPU can’t perform a DIV/MOD operation fast enough to display decimal numbers), it is stranded and unable to continue its mission.

Space Rocks joystick interface

We were not able to locate an original controller, but the interface is similar enough to more modern analog joysticks that we could wire it in. Have your own vector display? spacerocks.c is the source for the Teensy to drive it.

 Posted by at 10:07 pm
Jun 062013

Model 15 rear view

The Teletype Corporation Model 15 “typebar page printer” is a beautiful piece of equipment from the 1930′s. While the interface has much in common with modern serial communication standards – start bits and stop bits, asynchronous clocking, idle-high conditions — in the teletype all of these are implemented purely mechanically. The mainshaft looks like something out of an automobile instead of a piece of computing. Just like a car, you have to keep it well oiled, check the gaps for proper clearances and be very wary of the spinning pieces while working on it.

The 5-bit Baudot words are clocked in synchronously with the mainshaft’s rotation rate at 45.5 baud (22 ms per bit). This slow speed is difficult to generate with modern computers and serial ports, so many users bit-bang the port with Heavy Metal, which itself requires somewhat older machines to run. The 5-bit word has only thirty two entries, which is insufficient to simultaneously represent the entirety of the twenty six letters A-Z, ten digits 0-9 and punctuation. Instead there is a reserved code to switch to Figures and another code to switch to Letters. Space, carriage return and line feed are present in both the Letter and Figure sets. The interface must track which rail is currently selected and insert the correct shift sequences on the fly.

In slow motion the holding magnet can be seen pulling the selector during one-bits and not attracting it during the zero-bits. Each bit is latched via the “sword” mechanisms onto one of the rails, which select one of the twenty-eight hammers. During the fifth bit an extra gear cocks the mechanism and a latch lets the hammer fly during the stop bit. The coils are designed for 60 mA, but have a very high inductance (on the order of 4 Henries according to John Nagel). Most approaches to interfacing with the system use a large 100 VDC power supply and a current limiting resistor (that must dissipate 6 W of power!).

Teletype Model 15 USB interface board

Both the high voltage and the custom baud rate issues are a bit cumbersome, so I thought there must be a better way. USB ports will output about 5 W, so I figured that would be close enough to drive the magnet if I could produce sufficiently high voltage. Using Adafruit’s boost converter calculator, I came up with some rough numbers and built a circuit that handles both the slow baud rate and voltage required to interface with the teletype. It shows up as a normal USB serial port and handles the 7-bit ASCII to 5-bit Baudot translation, including tracking which of the two rails is selected, outputs the bits at the correct baud rate, and runs the PWM charge pump to generate the high voltage with the inductor. A second MOSFET is used to switch the high voltage through the current loop, allowing the holding magnet to turn on and off.

It’s fully self-contained, fits in an Altoids tin and works with any software you want to run on the interface computer. If you want to run it with a Raspberry Pi, be sure to use a powered hub to avoid overloading the Pi’s weak USB power circuitry. The schematics and source code are posted to and you can see it in action as part of Future Crew at the digital archeology themed 2013 NYC Resistor Interactive Party.

 Posted by at 7:53 pm
May 272013

Oscillograph tweet reader

It’s a little known fact that during the 1940′s the premier Twitter client was a cathode ray oscillograph vector display, such as this DuMont Labs 208B. The 15×12 character resolution was perfect for a 140 character tweet. This one has been restored, connected to the aethernet and configured to search for “I”, turning it into a time travelling view into the twitter-sphere’s narcissism. You can see it in action in this short video, or play with it in person at the 2013 NYC Resistor Interactive Party in June.

Asteroids vector font

If the font looks familiar, that’s because it was inspired by the Asteroids video game, with additional characters for the rest of the ASCII subset. The source code is available asteroids-font.c for your own oscilloscope or vector display hacking. Depending on the bandwidth of your scope and the speed of the cathode ray tube, you might need to set CONFIG_SLOW_SCOPE to give the beam time to catch up with the image.

 Posted by at 10:25 pm
May 232013

Building "Future Crew" console #1

Do you enjoy playing Space Team, but find that you want tactile controls? Or like the Artemis Bridge Simulator, but think it is too serious? Do you love pushing buttons, turning knobs and shouting at each other? Then you’ll really have fun playing Future Crew at the NYCR Interactive Party!

Future Crew push button panel construction

Since the theme of the party is “Digital Archeology”, all of the control stations are being built from repurposed dead hardware. There’s a patch panel, push buttons, strobe lights, more push buttons, quadrature knobs, oscilloscopes, and maybe even a teletype to keep score.

Future Crew display console

Each console will have a Raspberry Pi with Wifi to talk to the other consoles, some number of Teensys to talk to the real world, and some sort of glitchy way to communicate to the operator (like an NTSC TV or a Minitel). If things don’t work right, that’s part of the fun. And, of course the source code will be available for you to build your own Future Crew Consoles.

Tickets for the party are on sale now!

 Posted by at 8:12 pm