Retro Computers

The High Nibble is back with another fun retro computer kit. This one of the Cromemco Z-1. I reached out to the creator of the kit when it first went up, and he asked if I was sure I was interested. The kit is 99% the same as the IMSAI 8080, including most of the components except the acrylic panel and new firmware. The kits are so similar the PCB for the main board is the IMSAI 8080. I enjoyed the last one so much and wanted to support the creator (not to mention a new kit means more blinky lights on the shelf); thus, I ordered the new kit.

The kits are not cheap at $300, but come with everything you need, including a ready to go controller. The packaging is done well with individually slotted spots for each switch and IC in cardboard. The metal case is a nice touch. And just like before, the firmware is fantastic. You get a full web interface, external serial ports, the gorgeous front panel, and the system can update over the air update via Wi-Fi.

I won’t go too in-depth about the kit because it is so similar to the other one. The soldering is not too bad, the process starts with one small IC that has to be soldered in the front of the pcb, after that things like sockets and LEDs are easy, large, and straight forward.

I got a new soldering iron, the Pinecil from Pine64. This was my first project using it and I found it delightful. It’s smaller than my old iron, making it easier to handle. It’s advertised as a “smart” soldering iron which means when you put it down in a holder it quickly cools when not in use. A very nice safety feature.

The parts of the last build that were difficult are here too, having to put the system together as a sandwich of acrylic and circuit boards it’s a bit tricky, but once you get it in the right spot tightens up easily. Tape helped keep the build aligned during assembly.

The website for the project has a lot of good information, https://thehighnibble.com/cromemcoZ1/. There’s also a helpful YouTube video, same one as the IMSAI kit, that walks through the construction step-by-step.

The main step that gave me an issue was when you get to Testing, the LS2 light would not come on. After looking in the forums, https://github.com/orgs/thehighnibble/discussions/120, turns out that is a difference in the firmware, and it is not supposed to come on. With the video being for the other kit, it is not mentioned.

Overall, another great kit, and another fun system to add to the collection!

As part of my LAN Before Time rack project, I’m setting up classic PCs with a VGA and PS/2 KVM to manage them. However, one of my systems—a 486—lacks a PS/2 port for the mouse. A simple PS/2-to-serial adapter wasn’t enough; it required a proper signal conversion to work.

After some searching, I found this adapter kit on eBay: PS/2 to Serial Mouse Adapter. It’s based on an open-source project: necroware/ps2-serial-mouse-adapter. The kit didn’t include instructions, and the project assumes you already know how to assemble it; I decided to document my build process step by step.

A Quick Note on KVM Compatibility

This adapter worked flawlessly when I plugged a PS/2 HP Laser Mouse directly into the 486. However, when connected through my KVM, it worked for a few seconds before stopping. After some digging, I found a pull request from last year that mentioned a KVM fix. Flashing that updated firmware completely resolved my issue! Unfortunately, the main repository hasn’t been updated in two years, so hopefully, it gets some attention.

What’s Next?

Below, I’ll walk through assembling the adapter. After that, I’ll cover how to flash the updated firmware using a USB-to-TTL converter. These converters are cheap and easy to find—here’s the one I used: USB to TTL Adapter. Finally, I will show a case I designed and 3D printed for the device.

Steps

Put the serial connector through the top side of the board and solder it in place on the bottom, starting with the mounting legs and using plenty of solder. These take a lot of the strain of the connections. Then carefully do each of the data pins, making sure not to bridge any.

Insert the lower chip socket, and solder in place on the underside.

The Arduino Pro has 3 different parts we need to solder. The first is the head with the 90 degree pins at the end. This will allow us later to flash the controller if we want to move to other firmware. Put those through the top (the side with the chip) and then solder them in the underside.
Next, put the Arduino header pins in the bottom. I put them into the header connector to hold them in place. Do not put too much heat on each pin with the plastic part below. (Not my best soldering job)

Solder in the 10k resister, here I am soldering it on the bottom while it went in through the top. After it is in, cut of the excess legs.

Solder in the PS/2 port, use a good amount of solder on the mounting points so it doesn’t move when inserted, then solder the data pins.

Solder in the micro-usb port, careful of the tiny pins.

Add the jumper pins, solder them in.
Now time for the capacitors, these are polarized, note the right side of the silk screen is white that should line up with the white side of the cap. (the shorter leg side)

Finish up by soldering all the pin headers for the controller to sit on the board.

The board should now be complete! If you bought it from the seller I did, (who has been great, and I have bought other items from) then you have the main repos firmware on it. I won’t go too far in depth for this, but if you clone the fork down you can then use Platform.IO to flash the firmware. There are guides out there to do this on. Platform.IO is great when doing Arduino projects.

If you go the same kit I did, then it comes with a “pro16MHzatmega168” not the “pro16MHzatmega328” used in the Pull Request. Change the two lines where the 328 is mentioned to the 168-model string. If you do not, you will get a “timeout connecting to Arduino” when attempting to flash.

As mentioned, you need a TTL converter, then to flash the chip. The TTL converter (which I hadn’t used before) pins actually line up with the pins on the Arduino Pro. You need to hold it there for a total of 30 seconds while it flashes. You can just stick the header pins of the Arduino through the holes of the converter, then hit send via Platform.IO.

Flashing the new firmware on my messy desk, I did not need long cables like this…

3D Printed Case

This is a device I will keep behind my old PC, and I didn’t want it to be a raw circuit board. I didn’t see any cases to 3D print, so I put one together. This was the first time I made a case that used little feet to snap the top and bottom half together; no screws! I also put little towers in to hold down the PCB in place. It took a few revisions, but I think came out nicely. There is also a little window to hit the reset button if needed. The black case was the second revision, the white case is the first.

Model: https://thangs.com/mythangs/file/1301661