Thirty years ago in 1983 the first tablet computer was released: the Tandy / RadioShack TRS-80 Model 100. It ran for weeks on four AA batteries and gathered quite a following. Despite the $1099 ($1399 with extra 8-KB of memory) introductory price tag, features like the built in 300 baud modem with acoustic couplers made them very popular with reporters in the field, and the built-in BASIC programming language (written by Bill Gates himself!) made them easy to adapt into various custom applications. Over six million were produced and as a result, inexpensive, used Model 100s are readily available now. Amazingly many of them still work perfectly and there is a somewhat active Club100 fan club.

I bought one that was non-functional for $20 with the goal of replacing the 80C85 motherboard with a more modern AVR or ARM CPU. While this particular motherboard had failed sometime ago due to bad capacitors, the LCD and keyboard were in perfect working order. Thanks to the combination of the age of the design, the system’s low original clock speed (2.4 MHz) and its 5 V logic make it simple for modern hardware to drive. Moore’s Law also means that the entire motherboard can be shrunk into a PCB with almost zero chips other than the MCU. Read on for what is involved in building a new brain for your Model 100. Continue reading »

I was inspired by Beth’s avrfid.S project to try to build a replacement for the multiple HID Prox cards that I carry for work. Her design is simultaneously a technical tour-de-force and an example of how badly we can abuse the Atmel chips. Here is the entire schematic:

There is no connection to power and ground: the chip is powered through leakage current from the input pins. The AC waveform is fed directly into the pins: the internal protection diodes rectify it. During negative parts of the wave the silicon die’s inherent capacitance maintains state. The CPU clock is driven by the AC as well and depends on the ability of the coil to drive more current than the chip when DDRB is configured to pull the pins to the same potential. It’s truly amazing that this works at all.

The firmware she wrote in macro assembler is easy to understand and straightfoward, but filled the entire 8 KB flash on the ATTiny85 when compiled for HID Prox cards. Unlike the CW modulated EM41xx cards that just load the coil for thirty RF cycles to send a baseband one and don’t load the coil to send a baseband zero, the HID cards use Frequency Shift Keying (FSK) modulation. In FSK a baseband zero is sent by cycling the load on the coil for 50 cycles at a frequency of 4 RF cycles, and a baseband one is sent by cycling the load every 5 RF cycles. Beth’s code loads the coil by setting the two bits in DDRB to 1 while holding PORTB at 0, which places a short across the coil by putting both ends at the same potential.

While it turns out that my dream of automatically selecting the right RFID card doesn’t work, read on for details of how to build your own HID compatible RFID devices and some overview of the hand-tuned assembly necessary to fit the RFID timing. Continue reading »

Introducing Make-A-Long, a new monthly crafting event at NYCR.  Make-A-Long is a self-guided craft workshop where participants learn new skills, explore new materials and make great things!

In this session we’ll explore the wonderful world of felting using carded wool (also known as wool roving).  Using water or needles, wool roving can be manipulated to form a myriad of different shapes.  Learning how to felt means you can make things like:  felted soap, felted creatures, felted jewelry, felted ornaments and more!

Are you a beginner? Don’t worry! We’ll provide instructions and materials for a variety of projects.  Facilitators will be available to help guide you through a project of your choice.

Are you a master? Bring a project, use our materials and hang out in a great space while doing what you love.

Sign up here: Make-A-Long:  Felting With Wool Roving, December 15, 5-8pm

Knitting has always been one of those activities that I’ve coveted. Fluffy sweaters, intricate scarves, little baby kimonos (oh wait, that was one of my failed projects…). And as if the results were not cool enough, I also just loved the idea of the community around it. Unfortunately, although I’ve always loved the IDEA of knitting, I… well, I really really suck at it. Then I found out about knitting machines.

I’m not sure how but somehow I’d stumbled upon a knitting machine hack by Becky Stern and the idea of hacking an electronic knitting device to do my bidding was way too enticing. It turns out that I’m a bit late to the party. Since the hack was published, those particular knitting machines had shot up in price. I mentioned it and it was hudson who’d first spotted something labeled TOYOTA hanging out at Resistor. It turned out that it’s one of Kelbot’s machines. She graciously loaned it to us for an evening to play with and play we did. The photo below shows our (ahem, my) first mistake. Since I didn’t know to add weights to the first row of the item, it quickly went south.

But not to worry! What’s a little hacking without some help from friends? Others quickly swapped in to help untangle the mess. There were 4 of us consistently poking and prodding at the machine, another that was shooed away, and in our moments of wonderment, we even started a google hangout with Kelbot for advice. (confession: not sure if any of us really wanted to RTFM but it turns out that the manual isn’t too shabby). Anyway, at any given point when one of us would grow bored/annoyed/whatever with the machine, someone else would step in to poke at it a bit more. We finally got it to work and managed to knit 512 lines of a gorgeous… umm… scarf? I then “hand embroidered” Adam’s name on it. Our awesome output is shown here.

It was a super fun night amongst friends so it turns out I got the best of both worlds, my first (perhaps not my last?) stab at a knitting machine and a community to dork around with. Additional photos can also be found here. And lastly, Kelbot did a great teardown of this beauty here for those who are interested in the innards of this workhorse.

I found Matt Joyce’s HDSP211x alphanumeric displays in the LED bin at NYCR and loved the StarTAC style. He had previously written about driving them, but using an Arduino and a shift register on a breadboard was a bit large for my goal of making it into a wristwatch.

I noticed that the PDIP spacing was the same as the Teensy 2.0 and, much like my ROM dumper, hoped that it could fit on the back of the display with almost no additional wires. Read on for the “schematics” and source code details.
Continue reading »