My own retro computer system

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nsoatw
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Joined: Mon May 12, 2014 6:13 pm

My own retro computer system

Post by nsoatw » Mon May 04, 2015 10:46 am

I've started a project that tries to recapture my love for the old home computer concept, where there is a main unit that is expandable via cards. Like a cross between an Apple 2 and PC/XT.
I've designed and built an expansion bus with I2C, SPI, power and slot-select on each slot. 8 pins for each slot. This expansion bus is connected to a MicroPython card. Each card has a 256-byte I2C-eeprom for storing of parameters and type of the card. Plug and play.
The MicroPython card makes it very easy to prototype code, and it REALLY feels like in the 80s: just flip the power-switch and start coding!

I started experimenting on a bread-board, and so far I have also soldered an expansion-bus (4 slots) and one SRAM-card. Future plans are sound and graphics that probably will be based on cheap AVRs.

I'm making all this just for the fun of it, and have no plans to do anything practical with it.

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kfricke
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Location: Germany

Re: My own retro computer system

Post by kfricke » Mon May 04, 2015 10:53 am

Sound fun, somehow.

If you can use the UEXT interface, you could use some interesting and ready-to-play-with modules.

nsoatw
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Re: My own retro computer system

Post by nsoatw » Mon May 04, 2015 2:44 pm

Yes, my bus is actually like UEXT without the UART-lines. I won't use those modules though, as I want to have fun doing my own HW and SW :D

nsoatw
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Re: My own retro computer system

Post by nsoatw » Sun May 31, 2015 7:26 am

Now with its own project page at:
http://hackaday.io/project/6025-skajntt

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pythoncoder
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Re: My own retro computer system

Post by pythoncoder » Sun May 31, 2015 7:59 am

Interesting. I've found SPI to be critical on lead lengths: I recently connected a device with 10cm leads and got occasional errors and bus lockups. I gather I2C has similar limitations.
Peter Hinch

nsoatw
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Re: My own retro computer system

Post by nsoatw » Thu Jun 11, 2015 11:26 am

When I use the bread-board I do have problems with long leads and 20MHz SPI. 10MHz with long leads or shorter leads, no problem. Proto-boards have been error free as well.
I2C have not been problematic at all. Lucky I guess.
Different chips seem to have different weaknesses though according to:
http://www.dorkbotpdx.org/blog/paul/bet ... in_3_steps

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danicampora
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Re: My own retro computer system

Post by danicampora » Thu Jun 11, 2015 11:59 am

When I use the bread-board I do have problems with long leads and 20MHz SPI. 10MHz with long leads or shorter leads, no problem. Proto-boards have been error free as well.
High frequency clocks and long wires are a recipe for disaster... The value of "high frequency" is bus dependent, in the case of I2C, going above 100KHz is already risky if you have long distances.

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