RetroPad

RetroPad v2.0

What is this?

This is an open source Commodore compatible gamepad similar in design to a Genesis or NES gamepad, but designed specifically for the Commodore and Atari 8-bit machines prior to the Amigas.

This project is part of the Nybbles and Bytes Commodore 128D programming series.

Why make this?

The author needed a joystick for her YouTube project, Nybbles and Bytes and felt that joysticks were too imprecise, troublesome, and wanted something more accessible. Gamepads fit the bill, but Master System and Genesis controllers used the wrong electricals and could cause damage to her systems.

Which computers is this compatible with?

The author has tested the initial prototype with a Commodore 128D, but electrically RetroPad should be compatible with any machines that support floating logic level inputs that are expected to be shorted to ground when the switches are closed (open-drain configuration, similar to I2C). This basically means it should theoretically work on the following machines:

• Commodore VIC-20
• Commodore 64
• Commodore 128, 128D, 128DCR, etc.
• Atari 2600, 7800, etc.
• Atari ST*

How was this made?

The schematics were put together using KiCad 5.0 on a Mac. This should be cross-compatible with any other platform KiCad 5.0 runs on. The author used the DigiKey KiCad Libraries to simplify footprint and symbol selection, so you'll want to download those and set them up globally. They were not included in this project repository as project-specific since that would effectively constitute a fork or redistribution which would then require their licensing. Plus, the project wouldn't get any updated footprints.

The STL files and models of the casing were designed publicly using the parametric modelling tool, OnShape. FreeCAD was originally considered, but unfortunately it's been too unstable for the author to use thus far.

You can get to the RetroPad Shell project in OnShape here.

Search for "RetroPad" in the public models archive and you can get the source models straight from there. For folks preferring to use a different modelling program, the STL files are also available with the schematics in this repository under the case/ directory.

The "RetroPad.step" file is actually just the 3D rendering of the PCBA.

Where is the BOM?

The BOM is very very simple at the moment, basically only using Omron B3F-1000 tactile switches straight from Digikey. Any 8mm pitch tactile switch with a similar profile to the B3F-1000 should work.

The connection to the computer is made using a 9-pin D-Sub connector. Any straight-through female to female 9-pin serial cable should work, supposing the housing allows for it.

Assembly is super easy since it's all through hole parts and two very large 0608 SMD resistors.

The generated BOM is available in the CSV file in this repository, but an actual BOM ordered by the author is available in the digikey.csv file.

How should I fab the PCB?

The author prefers to use OSHPark as the PCB fab house of choice, though with some finagling you could easily adapt to other providers such as PCBWay or others.

The original PCB is available on oshpark here.

How should I fab the case?

The author used her Prusa i3 Mk3s FDM 3D printer with a 0.2mm layer height and no support to print out the case. The model requires a high degree of precision in the printer, with a 0.1mm tolerance between the fire and jump buttons and the top half of the shell. The D-Pad area requires at least 0.5mm tolerance. You may have to file the parts down a small amount, depending on the resolution and precision of your printer.

Note that the case is designed to hold together using friction, so no fasteners are necessary. Also note that in the v1.1 design, there's not quite enough of a cutout for the cable strain relief to fit, so it may bow out a small amount.