F4/FMPAC Light Combo Board project

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By Alexey

Guardian (1922)

Alexey's picture

13-06-2015, 19:29

This is a sneak preview of the on-going project to put FMPAC Light by Jipe and F4 MSX2+ Register by Caro onto one board. The board will have to be installed instead of Z80 CPU and the CPU will be mounted on top of the board (in a socket). Below are the pics of the board prototype and schematics.



We are doing this project together with Dmitry Pugachev. Wish us luck! If anyone notices any problems with the current design, please let me know, thanks.

Alexey

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By igal

Master (211)

igal's picture

13-06-2015, 19:36

Very good Idea Smile

By DJs3000

Expert (104)

DJs3000's picture

14-06-2015, 00:06

igal, we took the scheme FMPAK from this topic. You are the author of the scheme? FMPAK works without BIOS?

By Alexey

Guardian (1922)

Alexey's picture

14-06-2015, 16:07

We found a problem in the schematics and fixed it. The prototype now works! Smile We are finalizing the design and ordering PCBs soon.

Video of prototype's testing

By jltursan

Prophet (2122)

jltursan's picture

14-06-2015, 17:02

Indeed it's a very good idea!.
As the Z80 goes in socket, add a turbo clock circuitry and you'll have the final internal expansion Smile

By usuario_msx2

Paladin (745)

usuario_msx2's picture

15-06-2015, 10:04

jltursan wrote:

Indeed it's a very good idea!.
As the Z80 goes in socket, add a turbo clock circuitry and you'll have the final internal expansion Smile

Yes,
for a msx2 is a very good expansion DIY kit.

By RetroTechie

Paragon (1475)

RetroTechie's picture

17-06-2015, 12:20

Suggested improvements:

*Use an SMD version Z80 like 8 or 10 MHz CMOS version in Flat Pack housing. Yes modders may prefer a DIP version in socket, but it would save a lot of pcb space.
*Same for the YM2413 chip, there's a -B version in SMD out there that's both smaller and more energy-efficient.
*I'd drop using a -12V supply, it'll be missing or broken on some machines. Bonus points for also dropping the +12V supply. 5V is enough to process an audio signal, and there's loooooottts of good, low power / low voltage opamps to choose from. IF using opamp(s) that is, if well designed, plain transistors might do.
*Power supply connections look thin.. Thicker traces for those is better, optimal is filling empty space with ground / Vcc surfaces.
*Check if board fits into an NMS8245. IIRC, Z80 is also under the floppy drive there, with ROM beside it, cartridge connector on another side, and a metal 'leg' that the drive sits on opposite of that. If you can't make that fit, you can probably forget about VG8230/35 machines too. Consider doing a version for those machines, that connects to the backside cartridge connector (flatcable under the board to empty space under keyboard).

By Alexey

Guardian (1922)

Alexey's picture

17-06-2015, 12:54

Thanks for your suggestions RetroTechie. Indeed using a Z84C0010FEC QFP processor could reduce the size of the board, however you will still have to have the connector to the mainboard size of Z80 in DIP package. Choosing 4558 and 2413 in SOIC packages will also help to reduce the size of the board. But I am afraid the board will still not fit to certain computers and will have to be connected with wires. For such computers a cartridge based board can be used: I have the plan to do such a board when we finish the existing prototype with Dmitry. There will be no need to put z80 on the board, but we can include the ROM chip as suggested in several FMPAC designs.

About 12V: we are using the ready-made schematics by Jipe that uses that particular voltage. Technically the 4558 amplifier can work from 5V as well, but then some components may need to be changed. Unfortunately I have no skills yet to redesign the FMPAC's amplifier to use only 5V.

I know that filling the unused space with "ground" is recommended, but in this case it complicates things a lot. Eagle CAD sometimes can't find an optimal way to connect the SOIC chips to the ground so it leaves the "air wires" on the board and they are barely seen. I haven't found the way to avoid using those, so I prefer not to use ground filling on complex boards.

Alexey

By Alexey

Guardian (1922)

Alexey's picture

21-06-2015, 19:07

Played around with Eagle CAD to make my own libraries for Z80 in PQFP44 and YM2413-F in SOP24. As a result, here's the board design that has only SMD type components.

If someone is interested, I can share Gerber files. I am not going to order these boards, I will order only the ones that are shown in the first post.

By DJs3000

Expert (104)

DJs3000's picture

18-07-2015, 23:52



By madscient

Master (177)

madscient's picture

22-07-2015, 16:24

Really interesting.
I want to buy at least 20 pcs if you can sell!

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