SillyTinySCSI - Smallest SCSI emulator! (ZuluSCSI OSHW)

[zigzagjoe]

As mentioned in the ZuluSCSI Pico thread, this is a firmware-compatible derivative of @rabbitholecomputing's ZuluSCSI OSHW with the goal of making the smallest SCSI emulator. It omits the Initiator and switchable termination of the full ZuluSCSI devices, but is otherwise feature-complete including the DaynaPort SCSI networking emulation.




Please ignore the hair so helpfully contributed by my cat
To give a better idea of how silly tiny this is, here's a comparison against a BlueSCSI V2 Pico DB25.



Board files and schematics available here. I'll be releasing a small quantity of these in kit form with the SMD components presoldered. I'll post a thread in the trading post when it's time.

Important note! This may not fit all macs if the case protrudes nearby the SCSI port as in some Quadras/Mac IIs. Please see the picture above for the critical measurements. For those macs the default DB25 doesn't fit, this model of DB25 should work especially if spaced away from the board while soldering, but I have not tested this.

Kit Contents: 1x DB25, 1x Pico W, 1x SillyTinySCSI board, 1x 20 pin SMD header, 1x 19 pin SMD header, 1x 1 pin SMD header



Assembly is straightforward with intermediate soldering skills.

1. Solder DB25 connector to SillyTinySCSI board
2. Solder headers to SillyTinySCSI board
   1. be careful to avoid soldering headers that you don't bridge to the SD card housing. You may want to shorten the tails slightly.
      1. 
   2. recommend placing headers into Pico W (unsoldered!) then placing on the board to verify alignment. Then, tack a single lead on each header.
   3. 
   4. There is a one-pin header that goes with the 19 pin header to make a second 20 pin header.
3. Solder Pico W to headers
4. Test, then trim spare length from headers.

Note: Do not grab the SD card when trying to remove the device. It *will* break. Guaranteed. Don't do it!
Only grab the top and bottom of the device, not the sides. Unfortunately, there's not exactly a lot of room for a full-sized microsd socket. At some point I will likely come up with a 3d-printable case to help mitigate this.

 

[Aeroform]

Looks awesome!

 

[s_pupp]

I would love to put one of these on the back of my Mac Plus.

 

[joshc]

Looking forward to getting a kit.

 

[3lectr1cPPC]

Can this be powered via the USB plug on the pico board for systems that don't supply TERM power?

 

[Forrest]

The sensitive electronics are not protected from ESD

 

[zigzagjoe]

Can this be powered via the USB plug on the pico board for systems that don't supply TERM power?

Yep!

The sensitive electronics are not protected from ESD

I am working on a case design, but these aren't quite as fragile as vintage electronics - I personally wouldn't worry about handling it without a case.

 

[tt]

I am also hoping to get a kit when they become available. I wonder if a commercial version of this form factor will end up being made. It makes the BlueSCSI V2 Pico DB25 looks huge!

I could see it may be possible to design the case so that the drive is a small bump on the back that is protective enough to allow someone to put a compact mac in a bag without having to worry about it and take it off.

 

[zigzagjoe]

I am also hoping to get a kit when they become available. I wonder if a commercial version of this form factor will end up being made. It makes the BlueSCSI V2 Pico DB25 looks huge!

I could see it may be possible to design the case so that the drive is a small bump on the back that is protective enough to allow someone to put a compact mac in a bag without having to worry about it and take it off.

I think it'd be doable to leave it installed as long as it's a soft case. My goal is to keep it as short as possible with the case, with a little bit of reinforcement for the SD card and enough meat to grip.

I did a first run of 10 of these, of which i'm expecting to sell off 7. I'm planning to iterate the design one more time to improve manufacturability (ideally, all but the through hole by JLCPCB) at which point if demand is there I may continue to sell them.

 

[Stephen]

Love it!

 

[zigzagjoe]

Here's the first prototype case. I'm quite happy with the design: the LED is clearly visible, SD card goes in easily (and is sufficiently protected now), the BOOTSEL button is accessible by pinhole, and most USB micro cables fit just fine. Not pretty, but if it works?

My printer isn't the best of quality when doing ABS, so I don't know if I will be able to offer these with the kits.



Still narrower than the bluescsi, too! though it is about 10mm taller. Weight of 1oz/28g

 

[joshc]

Would you be able to offer a case with the kits?

 

[Crutch]

Nice work! Cute as a button.

 

[cobalt60]

This is awesome, great job, and thanks for sharing. A 50 pin variant for internal SCSI connectors might be cool. The beautiful thing about open source is it would be easy for anyone to try this based on your design files. If someone wanted a full size SD, again, easy. And thank you RHC!

 

[zigzagjoe]

This is awesome, great job, and thanks for sharing. A 50 pin variant for internal SCSI connectors might be cool. The beautiful thing about open source is it would be easy for anyone to try this based on your design files. If someone wanted a full size SD, again, easy. And thank you RHC!

That'd definitely be possible, though, for internal use I think @rabbitholecomputing's existing RP2040 design is probably a better fit. It's already quite compact, and switchable termination is important for internal use. To be honest, I would not have high hopes of wifi working when mounted internally: The Pico W is not particularly sensitive so range is rather poor even when used externally.

Production update: I am making cases. While they are visually a little rough, they're solid ABS and are nicely durable.

With my Bluescsi I get frustrated as it's easy to miss the SD card slot (and then drop the card loose in the case) unless you're very careful about it. To address that, these have a little plastic guide mounted underneath the pi pico to make it impossible to miss the SD card slot. It also reinforces the slot. Makes it much easier to insert/remove the SD. The white line that can be seen on the case is to denote the side towards which the SD label should face, and the final will have a sticker with the name on the rear.

For this first batch I'm thinking I will assemble the entire device myself rather than doing kits. Parts due friday from Digikey to start building. After they're done and tested I'll start reaching out to those who have expressed interest.

 

[zigzagjoe]

Fabrication was completed over the weekend. I had a scare when my original unit stopped working, with some elements on one of its resistor packs not working. I thought I had an electrical issue, causing the elements to be blown, which meant I needed to rework things. However, it turns out it was not blown - it was broken. I'd fumbled my original board without its case at least once... whups.



So this wouldn't be an issue with the "production" ones, but I am going to do a little more testing while I'm at it. The production ones should be up for sale before too long. Case quality is not fantastic, but they're functional. If so inclined, being ABS, they are easily spray-painted. One unit has model primer already applied.

 

[reukiodo]

This is awesome! Do these work with BlueSCSI v2 firmware or only ZuluSCSI?

 

[zigzagjoe]

This is awesome! Do these work with BlueSCSI v2 firmware or only ZuluSCSI?

These use the ZuluSCSI Pico firmware. BlueSCSI firmware could be ported but I doubt it'd work out of the box on it as while the ZuluSCSI and BlueSCSI designs are similar they aren't identical. As far as I'm aware, they are more or less at feature parity anyways.

2 remain from the first batch - Trading post thread here. I ended up printing some black PLA cases to include also. The case models are here.

 

[reukiodo]

So the ZuluSCSI firmware can use the BlueSCSI WiFi, CD change, and file transfer DAs?

 

[zigzagjoe]

So the ZuluSCSI firmware can use the BlueSCSI WiFi, CD change, and file transfer DAs?

I know it can use the Wifi DA, but I am not sure about the CD changer/file transfer DAs.