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Commodore PET Projects - petSD+

petSD Revisited

Getting from this to this
Photo : Commodore Computer Online Museum Photo : Heather (SkydivinGirl)  



When I was trying to find a modern day replacement for my original PET 8250 disk system, I found that the options were pretty limited and discovered that, at the time, there seemed to be two options available :

PETDisk Designer's webpage My webpage
petSD Designer's webpage My webpage (this one)

PETDisk was the first floppy drive emulator that I found for the PET and it looked very interesting, I tried to e-mail the seller a couple of times without success, you may have more luck, but I then came across petSD.


The original petSD - Designed by Nils Eilers (Obsolete)

In a very similar vein as PETDisk, "petSD is a modern mass storage solution for Commodore PETs with [an] IEEE-488-bus. It can be used instead of and alongside vintage floppy disk drives. The petSD makes file sharing between the PET, the PC and the Internet easy."

The original perSD design is now obsolete and no longer available, it has been superseded by petSD+ (see below)

petSD offered additional capabilities beyond just floppy disk emulation, the board could be fitted with a Real Time Clock, that was fully supported by the software. Additional components to provide a USB connection to a PC and a 10MB Ethernet interface could also be installed, although software supported for these features was limited. 
Nils did not build petSDs for sale, until relatively recently, it was available in ready-built or d-i-y kit form from, a German language only website.

Unfortunately, due to heath issues, Donald, the owner of the site, is no longer able to produce petSD and it appeared that I would not be able to find one, other than if one came up for sale on ebay or the like.

However, the circuit diagram for petSD, along with the parts list and firmware were available from Nils' website, so I wanted to investigate whether I could make my own.

I made contact with Nils, initially with a view to just making the original petSD available again, but instead, an updated version has now been developed - see below.


petSD Revisited - petSD+

During initial discussions with Nils, he suggested some changes that could be made to the design which would enhance petSD functionality, but would not have the same cost impact as his petSD-duo design (a much enhanced version of petSD).

My original plan was just to try and build a copy of the original petSD, but, going further than just suggesting some changes to the original design, Nils has now taken those changes and produced  an updated version of petSD, that we're calling petSD+.

Update : 15 April 2015

Nils had completed the design for petSD+ and had ordered a prototype PCB for final testing

(All photos courtesy of Nils)

Schematic of the completed petSD+ design
The KiCad 3D model of the board
Update : 27 April 2015

Photos showing the component and solder sides of the prototype petSD+ PCB, back from manufacture.

When test fitting the components, Nils identified a couple of minor issues as described on the errata link of his updated petSD webpage.

The issues are trivial and things were looking good so far.

Update : 1 May 2015

The first prototype PCB, with the majority of components installed

Update : 3 May 2015

Completed prototype - all components are now mounted, ready for the LCD display.

The display mounted on the prototype PCB

Rear of the display board, wired for connection to the petSD+ main board.
Update : 5 May 2015

Test fitting an almost bare prototype PCB in the case

Top half of the case mated with the bottom and a bezel fitted to give a nice tidy finish.

"Photo shopped" mock-up of how petSD+ might look with the LCD display fitted.

And the buttons too . . . . . .

Unfortunately though, although the proposed case for petSD+ was workable, Nils found that the installation was very tricky and time consuming, so was not really practical.


Update : 30 May 2015

By now, Nils had created the new firmware for petSD+ and been able to test the basic disk read/write functions, although the logic for the LCD display had not been included yet. A future firmware update would enable the LCD functionality and the boot loader will be able to reflash the MCU from a binary file copied to the SD card.

(New releases of firmware are compatible with all versions of petSD/perSD+.)

Based on his construction and testing experiences to date, Nils had made a few "tweaks" to the petSD+ design, mainly to correct the minor issues shown in the errata link on his webpage. Once these modifications had been finalised, a new batch of prototypes was ordered (Board Revision 1.1)


A photo of my (courtesy of Nils) petSD+

It wasn't easy to get a good photo of the device which also showed the display clearly. In this photo, a separate photo of the display has been superimposed for clarity.

The display message means that the firmware currently does not use the LCD display :-)

Update : 11 June 2015

I had finished documenting the steps required to assemble one of the petSD+ prototype boards.

Nils provided photos and commentary that he compiled when assembling the first prototype. The page is available in both English and German.

Update : 1 August 2015

Nils had added the first LCD functions to the NODISKEMU firmware - a petSD+ hardware diagnostic screen.

See here for the details


petSD Availability - 2015 (as petSD+)


petSD was designed to be constructible by the average electronics hobbyist, and one of the design goals was to be able to use through-hole-technology (THT) components, rather than surface mount chips. The one exception was the FT232RL USB-serial-adapter for which a THT equivalent was not available. The USB - serial adapter has been dropped from the petSD+ design, the only surface mount component remaining is the SD card reader.

Although my initial interest was driven by my desire to get a petSD for myself, with Nils' permission, I decided to take on production of a few kits of parts and  manufacturing a few devices to make petSD+ available to anyone else who might be interested.

Assembly of the petSD+ kit is described on the Assembly page.

I have limited skills with a soldering iron, the surface mount card readers are rather awkward to work with, so I would prefer people to buy a kit of parts and assemble petSD+ themselves. However, for anyone not confident in their ability to build their own, I am prepared to build them for you.

When I asked for input on the prospective supply options, I had the following responses :-



Manufacturing & supplying a bare board


Manufacturing & supplying a bare board and the necessary parts to assemble it


Manufacturing, supplying & assembling a completed and tested board


(No preference)

Last Update : May 8th 2015 Total 8

Based on the limited number of responses, supplying a kit of parts seemed to be the most popular option. I decided that I would make kits available, as well as pre-assembled units for folks who need one. In practice though, once the kits and pre-assembled units be case available, the majority of people wanted a pre-built one.

A modified version 2 PCB is currently being designed by Nils, but this may take a little while to make it into production. In the meantime, a slightly modified version "1a" board was produced that corrected the MISO connection issue described in Nils' errata link on his web page. (This issue is only relevant to petSD+ boards that have the ISP port connector fitted which will not be needed by most users anyway).

Kits of parts and fully assembled petSD+ devices based on the Version 1.1 PCB are now available for purchase :

Please see the Ordering page for details


References :

Nils Eilers petSD home page

Donald's internet shop

The Vintage Computer Forums - petSD thread


Credits : Heather (SkydivinGirl)

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