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Forum Index : Microcontroller and PC projects : Something I've been playing with

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knivd

Regular Member

Joined: 07/09/2014
Location: United Kingdom
Posts: 72

Posted: 06:49pm 24 Sep 2022

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...two challenges at once.

First, to build the world's thinnest DIY computer, and second to write a new BASIC interpreter (for it).

I dare to say, I am pretty happy with the results from both.
See the pictures - 2mm thickness!!! To achieve that, I resorted to some unconventional method of building - component-through-PCB.
Overall complexity - 9 components.

This system is not aiming at breaking records (except for the above, plus simplicity), but rather a starting point for development of similar but more capable systems. This initial one is built on a PIC18 with 13K of RAM and 128K of flash (64K of which is reserved as "hard disk").
The keyboard is probably my biggest achievement here - it works as dual role resistive/capacitive keyboard, can be used in any conditions with either bare hands, or with contacts, and all that on a MCU with no capacitive controller!

In terms of battery life - massive. The system draws 2.1mA at maximum load, and less than uA on standby, so many, many hours of work on a single charge. And years on standby. Does not include a charger on board, but the battery can be charged through the expansion port.

The BASIC actually turned up quite reasonably good and extremely memory efficient. It can work on devices with as little as 2K of RAM, is non-recursive (hence, no stack requirements), and on this new computer which runs at 8MHz clock, executes at approximately the same speed as an Apple II. It is also reasonably forward compatible with the MMBASIC, but also includes a few things of its own. For one example - it works with the BASIC-standard round bracket array index, but also with (much more readable) square brackets. Keywords which are built from two words (eg. END IF, END SUB, etc.) are supported either way. Strings are of unlimited length and dynamically managed to use minimum memory, etc...
It also includes a decent text editor, similar to the one in MMBASIC, and can communicate with the external world through an expansion port, and also transmit/receive files through XMODEM. All that, on a resource-constrained 8-bit MCU with half the flash to spare for file storage.

Of course, never expect the comprehensiveness of the MMBASIC, which has had more than a decade of development, and is generally aiming at higher resource systems, but this one on its own is quite fun as well.

I will have to take on the unpleasant task of documenting it all now, so will post more sometime in the (near) future...

PeteCotton

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Joined: 13/08/2020
Location: Canada
Posts: 543

Posted: 07:10pm 24 Sep 2022

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WoW! Brilliant job!

thwill

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Joined: 16/09/2019
Location: United Kingdom
Posts: 4311

Posted: 07:18pm 24 Sep 2022

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Awesome. Reminds me of the credit-card calculator my father brought back from a Japanese business trip almost 40 years ago. It's a real shame that mobile phones (dreadful things) have basically destroyed the market for more interesting ultra-portable computing devices (loved my Psion 3a).