Aquarius Mini Expander 1-1-0 - Rev C, 14 FEB 2021

by Sean P. Harrington, [email protected], http://aquarius.1stage.com

Since the Aquarius doesn't do much on it's own, and playing games on the chicklet keyboard is annoying, adding the functionality of the Mini Expander is essential. The Mini Expander expands the sounds to three voices, adds both a RAM and cartridge ROM expansion slot, and has ports for the Aquarius control pads. But since many Aquarius users DON'T have easy access to these devices, particularly in Europe, it was essential that this PCB be made available.

The purpose of this project is to document the stock Aquarius Mini Expander, both in schematic form and in board layout. An excellent document from Radofin exists that records the original schematic for the device, and it was used to verify the components and layout of this project, but there are a few, minor discrepancies that have been corrected based on ACTUAL board layout.

Also, this board serves as a useful prototype for how the expansion bus can be used on the Aquarius. By observing how the AY-3-8910 sound/IO chip is interfaced to the address and data bus, users who want to create their own expansion device could do so. Since it is already a very simple device (only about 25 components), the large footprint of the board could be improved through smaller SMD components and better trace routing, leaving plenty of room for additional functionality within the original (or modified) Mini Expander case.

To that end, an additional header for AY-3-8910 I/O has been added, along with detailed silkscreen markings on both the new header and the upper Expansion Slot so that hobbyists can experiment with creating their own expansions to the Aquarius. A reminder that the Expansion Slot pins are NOT like GPIO pins on an Arduino or Raspberry Pi. A0 does NOT mean analog pin zero, and D0 does NOT mean digital pin zero (nor any of the others). If you want to create your own I/O procedures, use the IO pins on the AY-3-8910 instead.

https://docs.google.com/spreadsheets/d/1Fgy7V73wTicvzhZblFc1MAg1R4uz7tYPBy140xyRtXA

• Aquarius Mini Expander v1-1-0 PCB Rev B, 09 SEP 2020
• Electronic components (listed in BOM above)
• 3D printed parts
  • Aquarius Mini Expander v1-1-0 case BOTTOM
  • Aquarius Mini Expander v1-1-0 case TOP (in development)
  • Aquarius Mini Expander v1-1-0 case TRAP_FRONT (in development)
  • Aquarius Mini Expander v1-1-0 case TRAP_REAR (in development)
• Assembly screws (to be specified later)
• Trap Door springs (to be specified later)
• Trap Door hinges (to be specified later)

• This project does not incorporate any new functionality. Users who want to add functionality may fork this project on their own.
  • SD Card read/write is not implemented, such as on the Micro Expander, a project developed by Bruce Abbott
  • A RAM expansion device is not included, such as the 32kb RAM Cartridge, a product developed by Jay Snellen, III
  • A cartridge ROM expansion device is not included, such as the AquariCart, a product developed by Jay Snellen, III
  • Switchable use of ATARI or SEGA joysticks (despite the same DB9 plugs)
• For users who want to use RAM or ROM in either cartridge slot, jumper pads (solder) have been added to connect pin 34 (rear slot) and/or pin 44 (front slot) to GND. Use this at your own discretion, but understand that you can't insert two ROM cartridges and expect them to work. Using two RAM cartridges could theoretically work, but it has not been tested.
• To maintain original layout, the three interconnect wires are not incorporated into the PCB. They are indicated as "WIRE" on the PCB, which should be bridged with 22 gauge solid core, insulated wire.
• The L1 choke/line filter (33uH) is difficult to source. Users may simply bridge this gap with 22 gauge solid core wire, or they can use a 0 ohm ferrite bead.
• Two of the small Control Pad interface boards are included as breakaways on either side of the narrow part of the board. These must be removed before the Mini Expander PCB can fit in the stock plastic shell. These small interface boards are used to transition the nine wires in the joystick cable to the mylar conductive pad used in the Control Pads.

• Where can I get the PCBs?
  • https://www.pcbway.com/project/shareproject/Aquarius_Computer_Mini_Expander_PCB.html
• Will you build me a Mini Expander? I'll pay you!
  • I won't (WAY too much to do), but it's not too difficult to do yourself. Also, there are some in the Aquarius community who can build one for you.
• Where can I get a case for this?
  • 3D print one yourself by exploring the 3d folder of the project. I haven't had time to create the top half (there are some intricate trap-door things to model), but maybe someone in the community will model one to fit?
• What about Control Pads?
  • There is a prototype for the Control Pads within the project, but I haven't had the time to take it beyond the prototype phase. This is open source, so have at it!
• How is this project different from the Micro Expander?
  • Designed by Bruce Abbott, the Aquarius Micro Expander is similar to the Mini Expander in that it has an AY-3-8910 sound chip and a header for Control Pad input (NOT joystick ports, a pin header). The Micro Expander is different in that it has a 32k memory expansion in it, a USB port, a 3.5mm audio port, along with a custom ROM that features a PT3 music player, USB ROM reading access, and a customized version of BASIC. The down side is that it blocks the Expansion Port of the Aquarius, so cartridge-based ROM programs (SNAFU, Nightstalker, D&D etc.) can't be used (unless you have the ROM image to load through USB).
• Why can't I use the A00-A15 expansion pins as analog input/output, or the D00-D15 as digital input/output for my Arduino experiments?
  • First of all, these pins are NOT analog and digital input/output pins! They are DIRECTLY connected to the address bus and the data bus (hence the A00 or D00 markings). Unless you know how the timings of these busses work, you're more than likely going to damage your Aquarius. If you want to experiment safely with TTL level inputs and outputs, use the IOA0-IOA7 or IOB0-IOB7 pins on the AY-3-8910 header instead.