An expandable computer system I'm building and programming just for the fun of it.

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This is a computer system that I am building around a simple serial bus system. This project does not have a functional end-goal other than to have fun while soldering and programming.

Expandability and simplicity. I've designed a low pin-count bus named SkinnyBus8. It has I2C, SPI, slot select and power. 8 pins in total per slot.

Each slot has a separate slot select. When the slot is selected, it is possible to request info via the I2C-bus to a 256-byte eeprom that contains info about the expansion card. PlugAndPlay :D

The SPI-bus is used for the main function on each slot.

A MicroPython-board is the "mainboard", and I've built a SkinnyBus8 4-slot expander-card. Coding in Python to test the card-functions has been a true pleasure. Genuinely fast prototyping.

Boards built so far:
  • 4-slot expansion board
  • 128KiB SRAM
  • 128KiB EEPROM

Working, and awaiting a proper board is an MCP23S17 SPI-GPIO chip connected to a 40x3 alphanumeric LCD.

The name SkajNätt is the Swedish pronunciation of Skynet, and Nätt means small. One computer to rule them all...

  • 2020-05-07 On hold

    adam.klotblixt05/07/2020 at 10:29 0 comments

    This is a message to inform that I've put this project on hold. I might continue at some time in the future, who knows? BUT: the things I learnt on this project are heavily influencing my latest project:

  • 2017-03-10 PWM and its intricacies

    adam.klotblixt03/10/2017 at 13:05 0 comments

    I've been busy trying out, reading about and understanding different aspects of using PWM as a means of getting audio out. There are some hidden treasures and possibilities, as well as pitfalls, that I really hadn't thought about before.

    Having tried different solutions, I've now settled for a simplistic approach of using stereo 8-bit phase correct PWM. It sounds good enough without lots of complexity. Now onwards with the serial comms to send data to the soundchip.

  • 2017-02-05 More sound

    adam.klotblixt02/05/2017 at 07:14 0 comments

    This is the development board I'm using for the soundchip coding and testing.
    I just added PWM- and noise-channels.
    Running the Atmega328 at 16MHz@3.3V, which is slightly under-volted seems to work well. The MicroPython-board uses 3.3V, and I really would rather skip the voltage conversion if I can.
    2 "speakers" because the sound is full stereo :D

  • 2017-02-02 Sound!

    adam.klotblixt02/02/2017 at 13:22 0 comments

    I've started coding the sound expansion now. Working quite well. 4 channels stereo sound of 4 different types: sine, square, saw and triangle.
    Next up is some communication with SkajNätt, and then PWM-channels, noise and adsr.

  • 2015-10-28 Return

    adam.klotblixt10/28/2015 at 16:45 0 comments

    I have been away from this project for some time now. Had some fun coding a ZX81 demo :D

    My immediate plan for SkajNätt is to make a sound-expansion card using an AVR as a DDS (Direct Digital Synthesis) chip with stereo output. 8 channels of simple waveforms and noise, ADSR, volume and pan per channel. Hopefully an analogue filter bank as well. Perhaps some rudimentary player built into the chip.

    I've coded such things before, but not for the AVR. It'll be interesting to see how many of my goals I can reach with this.

  • 2015-06-01

    adam.klotblixt06/01/2015 at 19:35 0 comments

    Verified I2C and SPI functions of the MCP23S17 expansion card, everything works OK.

  • 2015-05-31

    adam.klotblixt05/31/2015 at 06:42 0 comments

    Built an expansion card for the MCP23S17. Time to test the connections now, before connecting chips.

  • 2015-05-29

    adam.klotblixt05/30/2015 at 07:48 0 comments

    I finally put up all the information I had on hackaday projects. More to come.

  • 2015-05-24

    adam.klotblixt05/29/2015 at 19:48 0 comments

    Soldered a proper connector for the LCD. Changed to PortB on the SPI-GPIO chip as the pinout was a much better fit for the LCD. Cleaned up the code quite a bit but still lacking string-output.

  • 2015-05-21

    adam.klotblixt05/29/2015 at 19:46 0 comments

    Connected a 40x3 alphanumeric LCD to the SPI-GPIO, wrote the first hard-coded setup and text to it.

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