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The cbmSD Project

Introduction

Welcome to the "cbmSD" Project Page! This is a project to simplify, cost-reduce, and size reduce Nils Eilers' petSD+ floppy drive emulator for 8-bit Commodores with IEEE or IEC interface. Nils' device is very nice, but I felt a form factor that plugged directly into the back of the PET with an IEEE pass-thru, basic features and low cost would be something that would appeal to a wider audience. My versions remove the display, buttons, and clock/battery. They also offload the SD support circuitry to a small pre-assembled 5Volt compatible module that is available at very low cost. This means the devices can be soldered completely with through-hole parts. It also means that the card could be relocated to a convenient location off-board if desired.

The boards plug directly in and provide a pass-thru for other devices. You do not have to buy an expensive IEEE cable if all you want is the SD card device. If you do have other devices they will just plug into the back. The devices can be powered via a small 5V adapter, or via the cassette port (with compatible adapter).

cbmSD-mini Version 1.2

This is a bare minimum card with minimum extras. It will only work on PET/CBM computers and does not have an IEC connector. It has no display, clock, switches or jumpers. To change device number you must use the computer and send commands to the unit - just like a real CBM drive. A nice DOS WEDGE would be a good idea to make using the device easier. This device is designed to use standard NODISKEMU firmware.

Version 1.2 is now available on github. The only changes are removal of the '125 chip, and the addition of a secondary SD card header for those that might want to have the SD card face to the back. I have tested a board and it is working as expected.

Dave Stevenson created a nice tutorial for writing the firmware to PETSD+ and this also applies to cbmSD-mini.

The design for the cbmSD-mini can be found on github along with gerbers for making your own boards. Here: cbmSD-mini

cbmSD-mini Version 1.2v

I have created slightly updated V1.2v that adds a vertical mounting option. Some components were shifted slightly to make room for the new connector. Boards have been ordered and have been tested.

cbmSD-xd

This is a variation of cbmSD-mini that uses two boards. A pass-thru board allows connection of power, then a single ribbon cable (rather than IEEE) is used to connect to the cbmSD-xd. The cbmSD-xd can be convenient placed so you can access the SD card slot and see the LED lights. No expensive IEEE cable is needed and you can still connect normal IEEE devices via the pass-thru. There are two versions of the pass-thru board. One has the same PET-EDGE connector as the computer, and the other has a 24-pin Centronics IEEE connector which is the same as on IEEE devices.

cbmSD

This is an enhanced version with a few extras. It will work on PET/CBM computers as well as any Commodore 8-bit with an IEC port such as the C64, C128, Plus/4 etc. It has no onboard display or clock. I thought people with both PET machines and C64 etc might like to have one device that worked on both. Without an LCD in a simplified design this would be impossible, so I felt like this should be something that can easily be selected via DIP SWITCH. This DIP SWITCH could also be used to set the device number. There is an expansion header that allows connecting an external display, buttons, lights and SD card socket. Also, there is a vertical mounting option so that the board does not stick out the back too far. This version will require specific custom firmware to support the IEEE/IEC selection via DIP SWITCH. This firmware is not available at this time.

Here are the cbmSD work-in-progress schematics, pcb, and board render. The design is subject to change!

Some prototype boards have been made and are currently being assembled and tested. The design is not yet available on github. Check here for additional updates.

Current Status Notes

Development started using Nils Eliers' petSD+ v2.4 as the starting point for the prototype. Extra features were removed and the design was modified to plug directly into the PET/CBM. Boards were designed and ordered. Prototypes were assembled; Thanks to my friend Waltermixx for assistance! From here it was decided to split things into PET/CBM only (cbmSD-mini and cbmSD-xd) and Dual IEEE/IEC design (cbmSD).

cbmSD-mini and cbmSD-xd have been tested to work fine on:

Quick Usage Guide