Hello all

[amenjet]

What sort of interface are you using here? Is the microcontroller appearing as a top slot device with ROM?

If I remember rightly it wasn't that advanced - I believe it was an 8-bit parallel interface + signalling where the Psion sent commands and read responses through the topslot. I did it all "properly" with regards to the Psion topslot interfacing rules, but no ROM involved, just a couple of tiny machine code routines in the Org2, loaded in to the memory to stay resident, and called as needed from OPL programs.

Ah, interesting, without the ROM circuitry it's quite a compact circuit. These days having a PCb made is very cheap as long as you stay within some limits of size and don't do anything 'fancy'. I use JLCPCB, might be worth a go if you fancy a more robust, smaller version.

I made a top slot adapter a while ago that uses a RP Pico, that can present a ROM interface and allows input and output and attachment to almost anything. Using the Pico means it is easy to change the ROM code, no programmer required, just a USB cable. There's a videos:

https://youtu.be/OjPG9-fXxJ4?si=elgnbxnDRpLgeqpq
https://youtu.be/E4JlnzxkZ0U?si=iUzIa2S-Xq3BZ6A1

All the code and PCB files are here:

https://github.com/blackjetrock/psion-org2-top-slot

I made an assembler so I could assemble the code for these sorts of projects in one step. It's here:

https://github.com/blackjetrock/psion-org2-assembler

[jbuc]

Ah, interesting, without the ROM circuitry it's quite a compact circuit. These days having a PCb made is very cheap as long as you stay within some limits of size and don't do anything 'fancy'. I use JLCPCB, might be worth a go if you fancy a more robust, smaller version.

It's crazy how things have progressed for PCBs..."back in the day" it would have been impossible to knock up a topslot PCB due to the limitations of the etch resist pen and/or my dodgy over/under etching...now it's easy! (I have tried JLCPCB a few times, although nothing Psion related as yet).

You're right that the circuitry is "compact"..with a 5V micro it is basically just direct connections between the topslot connectors and the I/O pins - even a ROM wouldn't change that (unless I'm missing something?) as that would just be additional software in the micro.

[amenjet]

Ah, interesting, without the ROM circuitry it's quite a compact circuit. These days having a PCb made is very cheap as long as you stay within some limits of size and don't do anything 'fancy'. I use JLCPCB, might be worth a go if you fancy a more robust, smaller version.

It's crazy how things have progressed for PCBs..."back in the day" it would have been impossible to knock up a topslot PCB due to the limitations of the etch resist pen and/or my dodgy over/under etching...now it's easy! (I have tried JLCPCB a few times, although nothing Psion related as yet).

You're right that the circuitry is "compact"..with a 5V micro it is basically just direct connections between the topslot connectors and the I/O pins - even a ROM wouldn't change that (unless I'm missing something?) as that would just be additional software in the micro.

Yes, and with KICAd or similar designing the PCB is easier and less error prone.
You are correct that it's just connections between the top slot signals and a microcontroller with maybe some level shifters. And yes, a new ROm is just new flash data for the microcontroller.

[Daren]

Regarding the cases/enclosure I have seen some people get good results using a “low tech” approach for making small parts using silicone moulds and resin. It seems that quite intricate parts are possible with this method, the particular example which made me think it might be possible was someone making small action figures, they came out very well indeed.

I guess the main points of consideration would be cost and rigidity/strength, I have not looked into it in depth yet, but it does seem to be viable on both of these concerns.

The basic method is to make or find a suitable vessel large enough to contain the parts, mix up the silicone compound and pour into the vessel containing the parts and a plastic rod to facilitate pouring channel, tap the vessel to encourage air bubbles to the surface. Then once the silicone is set cut with a sharp blade in a zig zag to allow exact re-assembly once the original part is removed.
Reassemble the mould and tape around the cut, pour the resin mix and tap to remove air bubbles, let it set, the remove from mould, cut of spigot where fill channel was.

There are some tutorials on youtube if anyone is interested in doing this.

[amenjet]

Co-incidentally, I have recently bought a small vacuum chamber for degassing resin when moulding. It never occurred to me to have a go at moulding the cases. They are fairly complicated, but must have been injection moulded so I suppose they should be silicon-mouldable as well. Maybe.
I'm not sure how tough (acrylic) resin is, that's what I've been casting, maybe it's good enough.

[Martin]

Andrew and Daren

The degassing chamber is the answer. I've been interested in 'silicon' moulding the cases for a while but have never got around the 'degassing' of the resin. I'm sure they would be stong enough and as we discussed before they don't really need the locking clip for 'comms linking'.

Andrew.. If it would help, I'm happy to pay for the silicone and resin for the first trial batch if you don't mind trying it.

as always in good faith
Martin

[amenjet]

Andrew and Daren

The degassing chamber is the answer. I've been interested in 'silicon' moulding the cases for a while but have never got around the 'degassing' of the resin. I'm sure they would be stong enough and as we discussed before they don't really need the locking clip for 'comms linking'.

Andrew.. If it would help, I'm happy to pay for the silicone and resin for the first trial batch if you don't mind trying it.

as always in good faith
Martin

I think degassing will give you a much better surface finish, as it helps remove bubbles. I've been using Clearcast resin and that doesn't suffer so much from bubbles as it's designed for casting objects in transparent blocks. You could go through the process and not degas and see if you get a successful case, at worst it would have some defects on the surface, which could possibly be filled. It would be an interesting exercise, and the moulds could be used again in a vacuum chamber.

I'm up for a go at this, the only problem, as ever, is time. I also need to investigate suitable resins and silicone for the moulds. In the past I have used a two part silicone to make a mould, this probably requires a poured silicone. The other moulds I use are bought in. The resin I have, being transparent, would result in a case, but a transparent one, which isn't necessarily bad, as i suspect the bubble defects wouldn't be as obvious, but it wouldn't be a 'proper' case.