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https://github.com/cscott/xostick

Open Hardware design for a simple USB hardware device for the OLPC XO
https://github.com/cscott/xostick

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Open Hardware design for a simple USB hardware device for the OLPC XO

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README 

        
This is a simple Open Hardware peripheral for the OLPC XO-1/1.5/1.75/4.



The files are created using Eagle 6.2.0 on Linux and the SparkFun

footprint libraries.



Some details about the design:



1. Supporting using either the ATtiny85 (lowest cost) or the ATtiny861

   (14 I/Os, slightly more expensive).

2. Based on the Sparkfun AVR Stick

    http://www.sparkfun.com/products/9147

   and thus software will be based on

    http://www.obdev.at/vusb/

   Note that the USB port has been moved to PB3/4 so software for the

   SparkFun AVR Stick will not work without modification.

3. The PCB we're working with is 0.8mm (0.031"); a USB plug "is supposed to be

   2.4mm (0.093") but you can get away with 1.6mm (0.062")" (thanks, djgpp)

   Our solution is to put two breakaway tabs on the back of the board.  You

   can break them off and glue them below the USB fingers to make it stay in

   the port better/at all.  One gotcha is that break away PCBs tend to stress

   nearby traces; I've tried to give them adequate clearance.  We're also

   putting copper fills on the PCBs to make them thicker (thanks again, djgpp).

   The PCB we have also has 4 layers, but I've routed this board with only

   the top and bottom so that 2 layer reproductions will work just fine as

   well.  The inner two layers are ground and power planes, which don't

   need to be present to connect the ground and power nets.

4. I'm attempting to bring BOM below $1/student and part count down as low as

   possible as well.  As a result, we're skimping a bit on ferrites and

   bypass caps.

5. There are pads for populating a mini USB B connector, so you can

   put this on a cable (and avoid the glue-the-PCBs-together dance).

6. The XO Stick has a standard arduino shield pinout.  This lets it be

   piggybacked on another XO Stick for programming, or piggy backed on

   an XOrduino to control a turtle robot.  Standard arduino shields will

   probably *not* work, since not all pins are connected -- but they might!

7. To program one XO Stick from an XOrduino, the RST header on the

   target should be put in the "PROG" position so that the programmer

   can drive it via arduino pin 0.  To program an XO Stick from another

   XO Stick, both RST headers should be in the "NORM" position, and

   the programmer needs to have the RSTDISBL fuse programmed, so that it

   can use PB5 ('85) or PB7 ('861) as an output.  Note that once RSTDISBL

   is programmed, the device can't be programmed using the ICSP port

   until RSTDISBL is unprogrammed using the high-voltage programming method.

8. The XO Stick currently needs an external programmer.

   Can we write a USB DFU bootloader using v-usb?

   Something like:



        http://www.obdev.at/products/vusb/usbasploader.html

        http://embedded-creations.com/projects/attiny85-usb-bootloader-overview/

        https://github.com/embedded-creations/USBaspLoader-tiny85



  -- C. Scott Ananian, 2012-06-09; revised 2012-07-30, 2012-08-08