On April the first this year, there were many dodgy AI generated April fools posts.
Two posts that were produced without the use of intelligence of any kind, artificial or otherwise, were as follows:
And
That one was a fake, created by me in photoshop (by which I mean GIMP, but it seems to be accepted as a generic term, like "I googled it on Yahoo" or "I hoovered with the Dyson")
This took an entirely unjustifiable amount of time for what it was, but never mind, at least I didn't get cancelled.
The other was also obviously a fake, a Commodore SX-64, the portable C64, with a fake VIC20 screen showing on it.
Wasn't it?
No, it wasn't a fake.
It really is an thing.
Something TFW8b has been working for many years (with occasional input from me).
He even cleaned the screen for the video.
(well, sort of)
And covered over the place where future secret upgrades are to follow.
It has been a spare time project since before the pyramids were built. (well, since about 2018 which feels almost as long ago, when the world was a very different place)
Of course it has taken rather a long time as neither of us has much in the way of spare time to idle away on a frivolous pet project (or usually PET project in my case).
TFW8b is currently documenting the last 8 years work as this project might actually be drawing to a close.
Keep checking that post as it will continue to be updated until it is complete.
I will be writing a few posts on areas where there is more to explain, like the S-Video mod I covered last week, applied in a slightly modified form here.
In this post, I will expand on the power input side of things.
Powering the SX-20
It is important to say that no (good) SX-64's were harmed in this process.
This was not a mint, boxed, low serial number SX-64, signed by the entire cast of the A-Team.
For reasons of taste and decency, I will not include any more pictures of the donor SX-64. Let's just say it was in bad shape.
Someone had been through it and bodged and broke everything. Lots of wires were cut and some rejoined, connectors bodged, plastics cracked etc., and bits of the monitor board were rattling around inside.
It was bad.
It was also 120V, although I think the monitor was PAL. This really was a collection of broken parts someone made into the shape of an SX-64 and listed on ebay.
Which makes it the ideal candidate to become the SX-20.
Rather than having to use a stepdown transformer, or trying to modify the power supply (which looked to be fried anyway), it has been converted to 12V in.
With the power supply removed, there was a bit of space at the back where the power supply was.
Big enough for, oh I don't know, three large ex-UPS 12V lead acid batteries. 3.6Ah in total.
This is 0.0432 KWh, and just for comparison, an electric London bus battery pack is 400KWh.
The SX-20 is a step up from the SX-64 in that it is actually fully portable. No need to snake a mains lead out to beside the pool when you want to use your SX-20.
To make that work, it needs a new power board.
Version 1
This was the original version.
It worked, it did the job, but was a little sketchy.
Beautiful composed photo of load testing. It was Christmas break, so of course his test load was on theme.
(this was many years before the testers he recently built)
Ready to install.
I won't say anything about the wire colours, I will leave it to your own judgement to rightly conclude they are wrong.
That fitted in a space inside the SX-20 case.
But wait, there is loads of space behind that board.
Ah, perfect, just enough space for a Penultimate Cartridge.
To help explain what is going on, TFW8b helpfully drew a schematic.
I think that explains everything you need to know.
Version 2
That's more like it. The "less flammable version" from January 2024.
This does the same job, but with a revised design and implementation.
This uses three DC-DC converters with built-in displays to neaten things up.
Here showing the input voltages.
The schematic for this one is a little closer to the implementation.
I will redraw it to explain what is going on.
The SX-20 works in two modes, on battery and with 12V DC in.
To simplify this (a little), I will first draw those out separately.
SX-20 Battery mode
When running on batteries, the SX-20 needs power for three sections:
- The main VIC20 board (and accessories such as the Penultimate Cartridge)
- The monitor
- The 1541 disk drive
These are powered as follows:
The battery isolator switch and the main power switch both need to be on to use the SX-20. Congratulations, you have invented an AND gate.
The main 5V rail for the VIC20 and accessories is generated from the first DC-DC step down converter.
The VIC20 is almost entirely 5V DC, the only time it uses the 9V AC input is for the userport, and to generate the 6V DC for the datasette motor.
Neither of those are an issue here as they didn't fit when the photo of the VIC20 board was cropped into the photo of the empty case. (oh what a giveaway)
The 12V to the monitor is switched, to allow the monitor to be turned off to save power.
The disk drive power is also switched, with a separate 5V DC-DC step down for the drive's 5V rail.
The third DC-DC is not used.
I have drawn those as simple switches, but they are actually posh illuminated ones.
SX-20 12V DC in
When 12V DC is supplied externally, things are wired as follows:
Here the power switch controls the main 5V, the monitor 12V and the disk drive 5V and 12V, as before.
The third DC-DC converter is a step up to 14.4V to trickle charge the 12V batteries via the charge resistor(s). The battery isolator switch can be used to disable charging.
SX-20 Automatic Switching
The actual circuit used includes a relay which switches between those two modes.
The relay is powered by the 12V DC input. When that is not connected, it routes the battery to the power switch and disconnects the charger.
When 12V is applied, the relay connects the 12V input to the power switch and connects the battery to the charger.
Photos of the unit installed to follow, once TFW8b reaches 2024 in the photo archive.
More to follow I am sure, including things like the custom ROM I made for it, and I expect an upgrade to a PU+3 DCR.
So keep a check on the TFW8b post for more updates as he works his way through 8 years of pictures and maybe even some videos.
Adverts
For reasons currently unknown, the Tindie website is down, so I will instead tell you to go to TFW8b.com and buy something there.
(SX-20s are currently out of stock)
Patreon
You can still support me on Patreon, assuming their website doesn't go down before you read this post.
There I am currently working on the new Mini PET, with lots of development posts if you want to follow the progress.
