Nov 252013

In a show of solidarity with our oppressed Meleagris gallopavo brethren, there will be no craft night this Thursday, November 28th. We recommend gathering together with friends and loved ones and sharing a hearty seasonal meal of kale and pine nuts instead. See you all next week!

Nov 182013

AVR RFID with extra capacitor

Last year we wrote about building HID Proxcard RFID tags with attiny85 microcontrollers (based on Micah’s avrfid.s code). The C version only supported classic 26-bit cards, but I recently needed to support the “secure” HID Corporate 1000 35-bit format.

Based on Daniel Smith’s writeup on the format and some digging around, I figured out that the MFG_CODE for this format is 10-bits long with the value 0x005. He also pointed out that the 26-bit firmware had the wrong code — it is not the 20-bit code 0x01002, but is instead the 19-bit code 0x0801 and the bottom bit is part of the parity computation for the card id. If you’re using a HID branded Proxcard reader, the value that it outputs is the entire data portion, including all of the parity bits, but does not include the MFC_CODE part. If anyone knows of a table of these codes, please let me know!

I’ve updated my firmware with these changes and it works great. Emulating a 35-bit card takes 846 bytes of flash (nine more than the 26-bit cards since the state machine stores one bit per byte), so it might be possible to port this to the attiny10. I’ve also found that the tags work much better with a small capacitor across the two clock pins, as shown in the above photo.

Nov 162013

There was supposed to be an earth-shattering kaboom.

Just a reminder, no laser night tonight. You’re welcome to come by and hack instead! The laser is down but should be repaired by Tuesday!

Nov 032013

Photo by

I’d like to share a neat Eagle hack for all our the people who have taken our Eagle CAD classes (myself included) and our Eagle-using friends.

BOM-EX is nifty little ULP (User Language Program) that extends the functionality of the built-in BOM ULP. BOM-EX not only helps you assemble a coherent BOM (Bill of Materials) right from your Eagle schematic, but it also makes it easy to assemble a database of parts, and associate those parts with parts numbers for DigiKey, Mouser, Newark, etc.

I made a nice little script that lets me build my BOM database without ever leaving the DigiKey website…

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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.

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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