How to Make an Eight Bit Computer and Save the World!
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This document summarizes a talk given to introduce an open source 8-bit computer project called the Humane Reader. The talk outlines the goals of providing a cheap e-book reader and computing platform using open source tools. It describes the hardware design which uses an AVR microcontroller and interfaces like video output, SD card, and USB. The talk also covers using open source tools for development and sourcing low-cost fabrication and assembly. The overall goals are to create an inexpensive device that can provide educational resources in developing areas.
How to Make an Eight Bit Computer and Save the World!
- 1. SGVLUG 8 April 2010 How to Make an Eight Bit Computer and Save the World! Braddock Gaskill Humane Informatics [email protected]
- 2. SGVLUG 8 April 2010 Overview -Present Device -Overview -Goals -Device Demo -Functional Requirements -AVR Open Ecosystem - Uzebox -AVR Open Ecosystem - Arduino -AVR Open Ecosystem - gcc, avr-libc, avrdude -AVR Open Ecosystem - avrfreaks, uzebox forums, etc -Video Requirement - Tellymate -SD Card Requirement - Wave Shield/Uzebox -FAT Requirement - Petite FatFS -USB Desirement - V-USB -Schematic (Eagle, GEDA, gschem, PCB Artist) -Layout -Bill of Materials -PCB Fabrication -Assembly -Pricing
- 3. SGVLUG 8 April 2010 Talk Overview Today's Audience Independently Wealthy Philanphrapists Non-Governmental Organizations, UN, etc DoD Civil Affairs, USAID Geeks interested in Playing with Microcontrollers Building & Fabricating things Open Source Tools and Hardware Today's Talk Overview and demo of device Survey of AVR Open Source Hardware Survey of AVR Open Source Tools Walk through of design and design tools Walk through of fabrication and manufacturing
- 4. SGVLUG 8 April 2010 Bridging TV/Internet Gap
- 5. SGVLUG 8 April 2010 Bridging TV/Internet Gap Market >700 million
- 6. SGVLUG 8 April 2010 Pitch 2GB SD Card = ~5,000 books or better part of Wikipedia Humane Reader device turns any TV set into an e-book/wikipedia reader. Production Cost approx $20 (incl SD Card)
- 7. SGVLUG 8 April 2010 Value Proposition The Humane Reader can provide a virtual library to any developing world school or individual with electrical power for less than the cost of a single textbook.
- 8. SGVLUG 8 April 2010 Secondary Goals Goal: Create an extendable, hackable, 8-bit general computing platform both for first through third world developers and experimenters. Effect: Join and leverage the existing open source hardware community (Arduino, AVR, etc) to spur further development. Effect: Provide a learning platform as well as simple e-book reader.
- 9. SGVLUG 8 April 2010 Demo DEMO
- 10. SGVLUG 8 April 2010 Design Requirements NTSC/PAL Video Output SD Card Interface (w/FAT) Cheap Input Interface (buttons) Power (Micro-USB Adaptor) PS/2 Keyboard Interface (optional) USB interface (optional) Audio (optional) IR (optional)
- 11. SGVLUG 8 April 2010 AVR Open Ecosystem: Uzebox
- 12. SGVLUG 8 April 2010 AVR Open Ecosystem: Uzebox 8-bit gaming "console" FEATURES: NTSC/PAL color video output, game controller input, SD Card, custom "kernel", solid community FAILURES: expensive video chip, expensive MCU (Atmega644), overclocked design Too Expensive ($95 sparkfun)
- 13. SGVLUG 8 April 2010 AVR Open Ecosystem: Arduino HARDWARE: Simple break-out board with pseudo- standard expansion headers Wide variety of extension "shields" - Ethernet, Wifi, Bluetooth, SD Cards, video SOFTWARE: Provides an educationally-oriented "easy" IDE. COMMUNITY: Excellent. Dev tutorials, forums, etc CONCLUSION: Shield, IDE, and software compatible.
- 14. SGVLUG 8 April 2010 AVR Open Ecosystem: Tools avr-gcc compiler - full C, partial C++, bintools, well supported alternative to Atmel's compiler avr-libc - standard C library for AVR. Includes printf, etc (roll your own IO backend) avrdude - OSS Programmer - many methods simulavr emulator - several OSS emulators - waste of time (?) avarice - JTAG debugging. HW Expensive. Glitchy (-Os). AVR Dragon for <32k MCUs.
- 15. SGVLUG 8 April 2010 Schematic
- 16. SGVLUG 8 April 2010 Video Output REQ: NTSC/PAL Video Output PROBLEM: Very fast signal. For B&W, only a few cycles per dot. SOLUTION: Use existing Tellymate project software.
- 17. SGVLUG 8 April 2010 Video Output SOLUTION: Use existing Tellymate project software. Tellymate uses MCU's SPI device to output 9 dots at a time (~22 cycles per SPI buffer load @16MHz).
- 18. SGVLUG 8 April 2010 SD Card Requirement Interface: SD Cards have a simple 4-wire SPI hardware interface. 3.3V signal levels SOLUTION: 5V to 3.3V voltage dividers for MCU output, MCU can discern 3.3V input Power: SD Card needs 3.3V power theoretical (but not observed) current requirements are high. SOLUTION: Add 3.3V regulator 3.3V handling "inspired" by Uzebox schematic
- 19. SGVLUG 8 April 2010 SD Card Schematic
- 20. SGVLUG 8 April 2010 FAT Filesystem Several Open Source AVR FAT on SPI SD Card implementations WaveHC library for Arduino Uzebox FatFS and Petite FatFS (pFatFS - same author) SOLUTION: Petite FatFS Chosen for tiny size and simplicity AVR SD Card example required hacking - bad timings
- 21. SGVLUG 8 April 2010 FAT FS Issues Issues with FAT FS on SD Card Minimal RAM for caching (2kbyte MCU) Reading 1 byte requires reading full 512 byte sector from SD Card FAT random seek times LINEAR to seek position (VERY bad for 2 GB database). Solutions Minimal 128 byte cache added Non-fragmented file seek optimization
- 22. SGVLUG 8 April 2010 USB USB Power Micro-USB 5V power connector Micro-USB new world-wide cell phone charger standard = low cost USB Data Interface Arduino uses a serial bootloader w/FT232 USB serial chip FT232 more expensive, less flexible than adding a third Atmega for USB peripherals Open V-USB project provides firmware
- 23. SGVLUG 8 April 2010 USB Schematic USB provides regulated 5V power, but needs 3.3V data signaling
- 24. SGVLUG 8 April 2010 Free or Open EDA Tools Open Source GEDA Suite (as of 2005, when I last used them) gschem - schematic capture - "decent and usable" pcb - layout - "unsophisticated?" Cadsoft Eagle (freeware/commercial) Unixy-feel - scriptable, cmd line, mostly parsable text file formats Free for simpler layouts "Professional grade!" PCB Artist freeware, Advanced Circuits new, simple, but Advanced lock-in
- 25. SGVLUG 8 April 2010 Layout
- 26. SGVLUG 8 April 2010 PCB Fabrication Advanced Circuits Leader by far for fast-turn PCB fab Made in USA, great capabilities "What I use for prototypes" BatchPCB.com super low cost batch together low volume panels of individual orders for fab in China long lead time
- 27. SGVLUG 8 April 2010 Home PCB Assembly Prototypes assembled myself Tools for SMT home assembly Liquid flux w/needle dispenser bottle PCB cleaning alcohol and swabs Fine tip soldering iron desolder braid, etc GOOD tweezers Magnifier (Microscope) Hot air rework station Solder paste (optional) Good PCB vice
- 28. SGVLUG 8 April 2010 Suppliers
- 29. SGVLUG 8 April 2010 Enclosure #1 - No Enclosure Hobbiests require no enclosure #2 - Conformal Coating/Paint Conformal Coating - an acrylic gloss used to protect PCBs #3 - Plate/Spacer Sandwich Cost effective <1KU #4 - Plastic Case Tooling Cost Cost effective >1KU
- 30. SGVLUG 8 April 2010 PCB Assembly Screaming Circuits Leader in USA Asmbly: 100U = $27 per board! EzPCB China Set up for easy small runs Asmbly: 100U = $9 per board 1000U = $6 per board 10kU = $4.50 per board
- 31. SGVLUG 8 April 2010 The BOM Stops Here Manufacturer should cost optimize your Bill of Materials in quotation.
- 32. SGVLUG 8 April 2010 Production Cost *Does not include enclosure or SD Card
- 33. SGVLUG 8 April 2010 TITLE