The Sinclair QL Forum

Marcel_X wrote: Mon Feb 17, 2025 8:00 pm It's is based on the Pi Pico or Zero, but decided to include all components on a single 4 layer 1mm PCB to make it fit between the pins of a D-Sub15.

Nicely done. There is also a way to place everything directly into a D-Sub case:
https://www.theqlforum.com/viewtopic.php?p=50519#p50519
Schematics, placeplan and Gerbers:
https://www.theqlforum.com/viewtopic.php?p=50130#p50130

Can I ask whether you handsolder the RP2040 to your board? I was a little worried about that, so I used an existing module.

Hi Peter!

Yes, I saw your design. Great stuff! Well done! But I opted for a single board solution.
The board is not hand soldered nor placed by hand. I'm lucky to have access to a very professional pick and place machine with and a conveyor belt reflow oven. (Lucky basterd...!)
But with a decent soldering iron AND hot air gun and some skills, one should be able to solder it by hand.
The tricky thing is the exposed pad on the RP2040. That needs to connect to GND. On some microcontrollers there are additional GND pins that you can connect to GND and the exposed pin can be left floating (only connected to the die substrate) and is only used for mechanical strength. Not on the RP2040! The W25Q16JVUXIQ however does have exposed pads that can be left floating.

I'm ok with the current design, but my fingers are itching to make another revision without the extra D-Sub connectors....
Oh, schematics are attached for reference.

Cheers, M

Hi Marcel!

Marcel_X wrote: Tue Feb 18, 2025 1:09 am Yes, I saw your design. Great stuff! Well done! But I opted for a single board solution.

Thanks, but my design was just a primitive module carrier.
Yours is fully dedicated to the purpose, much more professional!

Marcel_X wrote: Tue Feb 18, 2025 1:09 am The tricky thing is the exposed pad on the RP2040.

That's the smaller problem for me, since I have an infrared station where I solder BGA as well.
I'm more worried about the fine pitch pads. I don't want to work with stencil and solder paste. For BGA the balls provide sufficient tin, but we don't have that here. I would need to solder from the side with a soldering iron. Maybe if I get the PCB tin-plated instead of gold, would it be sufficient tin?

Marcel_X wrote: Tue Feb 18, 2025 1:09 am W25Q16JVUXIQ however does have exposed pads that can be left floating.

As you mention flash, does the USB update mechanism work, if it is not pre-programmed?

Hi Peter!

I like that your design fits in a D-Sub shell!

If you manage to solder the exposed pad with your infrared station and if the RP2040 is properly aligned, then it is quite easy to solder the pins from the side.
I usually use a soldering iron with a chisel tip or hollow tip. Just solder the pins with plenty of solder. Even if you have some bridges or shorts, that does not matter.
Now comes the magic..! Apply a decent amount of flux across all the pins. Not the stuff you get from Aliexpress, but flux from Amtech. My favourite one is NC-559-V2-TF (or V3) Tacky Flux.
Next slide your tip across all pins on one side in one single motion. Magically all shorts are gone with the access solder sticking to the tip of the iron. Clean off and repeat on the other three sides. If you still have some shorts, re-apply flux and repeat. Clean off with some IPA (not the Indian Pale Ale ) and voilá you're done.

PCBs with a HAL (hot air level) finish don't have enough solder to connect to the exposed pad. But you can do the same trick here. Add a bit of solder to the exposed pad on the PCB.
Apply some Tacky Flux to it and place the QFN on top. I usually place it slightly skewed on purpose. Then I heat the board with a hot plate or hot air gun (but it should work with your infrared station as well).
When the solder starts to melt, you can see the QFN slide in place when the solder "grabs" the exposed pad off the chip. Let it cool and solder the pins as described above.

Sounds complicated, but it is not to hard once you get the hang of it. Amtech flux is your best friend

The USB mass storage is fortunately pre-programmed on the chip. I was a bit worried about that as well... But after connecting the first time it immediately showed up as a drive with a text file in it with the board loader version. Once programmed you can force it back into mass storage mode by holding the reset button while connecting USB. Same way as the regular Pi Zero or Pico.

Oh, and I just wondered if the QL Pico VGA also works on US versions of the QL. I read on Marcel Kilgus' website that some of these have a slightly different crystal and therefore the timing was a bit different. I think he managed to solve this in software. Anyone tested this?

Hi,

A while back, I got some PCBs made, but never got around to making the adapter:

I tend to get distracted easily...

But I was trying to use a Dsub housing, but is to small for the PCB, maybe have to use the Conec 16-001810E, but the unit price is expensive.

I like the new PicoVGA board, but I am not sure if I could solder the components, old eyes now...

Marcel_X wrote: Wed Feb 19, 2025 11:14 am I like that your design fits in a D-Sub shell!

Are you not tempted to do the same as a single board solution?
You could make it fit a less excotic case than the one I used.

Marcel_X wrote: Wed Feb 19, 2025 11:14 am PCBs with a HAL (hot air level) finish don't have enough solder to connect to the exposed pad.

That's no problem, I would add a little solder paste, no precision needed there.
But is it enough for the finepitch pads maybe?

Marcel_X wrote: Wed Feb 19, 2025 11:14 am The USB mass storage is fortunately pre-programmed on the chip.

Thanks for the info. I hate the huge development bloatware for the RP2040, but hardware-wise the chip is quite tempting.
I doubt the BOM costs for a homebrew design is lower than a finished module, but where space matters, it could still make sense.

Yes... I am very tempted to do so! I have already redrawn the board and squeezed it down to 26 by 38mm.
Have to tweak it a bit more. And instead of using a pre made shell or case, I modelled one myself.
Printed one, just to see what it would look like.
I already printed the case and it is a lot smaller than the one I made first And a lot more QL-ish

@Peter, regarding the soldering, I would definitely add some additional solder to the fine pitch pads.
Just add enough flux to the board, a little solder on your tip and drag it gently across the pads.

Does it make sense to make one from scratch? Definitely not!!!!
Just having fun designing stuff!

Here are some pictures and renders. I will order a few boards soon. I just need three or four so I probably have a few left in case anyone is interested.

hideehoo wrote: Tue Mar 07, 2023 12:16 am Another PCB/Case option I whipped up that uses the full size Pico, https://github.com/djtersteegc/video_if ... doc/pcb.md
pcb.jpg
case.jpg

Hi!
I have mounted this one,
and I wonder, how does it bring protection to the QL about +5v RP2040 power return ?

Thanks

Couldn't help it. I had to do it... Made the QLpicoVGA even smaller than the previous version. And made a new 3D printed enclosure instead of using an off the shelf one by Hammond. That one required a DB9 and a DB15 connectors on each end. And another cable with an 8 pin DIN and one more DB9 to connect it to the Hammond enclosure. I think this new solution is far more elegant and has the QL "look".
Single 1mm board that fits perfectly between the pins of an DB15.
I can put the Gerber files on Github if anyone is interested. And the enclosure on Makerworld for those with a 3D printer.