OPLxLPT adapter for ST/TT/F030

[nokturnal]

Hi,
Some time ago I started a small project to connect opl2/3lpt to Atari ST/f030. From pcb it looks like it started it last year :? .
In general I've rewired pins a little and created two test boards (with and without diodes (one version for easier debugging of Centronics/Printer port), second one for standard user). I'm not electronics expert, so sorry if anyone sees something very offensive. This is the very first PCB in my life, so probably isn't the best in the world. I've tried my best to not kill both opl3lpt and Atari (values of resistors are from ceiling on schema, so see photos for actual value, I use one type).

Wiring looks like this:

Code: Select all

OPLxLPT    CENTRONICS                    F030        ST
     1: A0       ->  /Strobe   CTRL-0   1 /STROBE   1 /STROBE
     2: D0      <->  Data0              2 /DATA0    2 /DATA0
     3: D1      <->  Data1              3 /DATA1    3 /DATA1
     4: D2      <->  Data2              4 /DATA2    4 /DATA2
     5: D3      <->  Data3              5 /DATA3    5 /DATA3
     6: D4      <->  Data4              6 /DATA4    6 /DATA4
     7: D5      <->  Data5              7 /DATA5    7 /DATA5
     8: D6      <->  Data6              8 /DATA6    8 /DATA6
     9: D7      <->  Data7              9 /DATA7    9 /DATA7
    14: /RD      ->  /Linefeed CTRL-1   +5V         +5V
    16: /WR      ->  Init      CTRL-2   11 /BUSY    11 /BUSY
    17: A1       ->  /Select   CTRL-3   17          GND             (OPL3LPT only)

Schema looks like this:

end-user version

opl3lptAdapterSchema2_800.png

development

opl3lptAdapterSchema_800px.png

Real thing like this (it's not final, because I will make it more condensed and nicer to connect):

pcb_opl3lpt_pcb.png

Problems:
I've got an issue with dev adapter and diodes. OPL3LPT is powered up from usb adapter and I stole 5v from pin 1 of usb port and wired it via resistor to pin 14 on OPLxLPT side, so it is in high state all the time (connected via resistor just to be safe).

When usb power is connected on opl3lpt side:
With connected D1 diode it light s up and is bright, but all other diodes don't light up at all.
With removed D1 diode. All diodes begun to turn on/off according to signal from lpt port(as expected), but are very dimmed (like current was really low and blue diodes, which are more power hungry don't lit at all - my test program which turns on/off data lines lits every diode beside blue ones).

With usb power is disconnected on opl3lpt side:
Everything works as expected, but d1 isn't lit, because it isn't powered up from pin 14. Diodes are bright.

Here is without usb power (state on f030 boot, /strobe and /busy set to high):

diodesIssue_002.png

Here is with usb power (state on f030 boot, /strobe and /busy set to high):

diodesIssue_001.jpeg

So, I've got several questions here.
1) Anyone more electrically competent could tell me what I'm doing wrong here and how to fix those issues with dimmed leds?
2) Data lines / signals are not suitable for powering diodes (bare wires), how I could protect them (psg and computer) better when attaching diodes? I imagine resistors aren't good enough.
3) There is no possibility to switch opl3lpt to read state right now, there is not enough signals on Atari side. Maybe anyone has suggestions how to overcome this? But it isn't very relevant, just nice thing to have.

Shortcomings:
Only f030 can enable opl3 features, because Select In line can be set to low/high. On ST there is no possibility to enable opl3 features right now.

Any suggestions welcome, still working on test programs/drivers for it. Unfortunately I haven't managed to produce any sound with it yet, so it's still work in progress (I've adapted sample tune replay by Daniel Illgen targeted for cartridge port, but still it isn't working as expected with this adapter, probably bad timings and/or still something hardware related I'm not sure).

Here are some better pics of adapters and opl3lpt with mods I mentioned above:

opl3lpt_mod.jpeg

adapters_opl3lpt.jpeg

[exxos]

I have only had a quick read but one thing to note about LED's, is if you are connecting them to a actual signal, then the LED can clamp it to basically a continuous logic low level.. You should always buffer them...

Similar if you are trying to light up LEDs on particular signals in series you can end up with a voltage drop .. where it will no longer register a logic high..

[nokturnal]

Yes, I thought about it and heard about term "buffering". But, I don't know how to do it, I'm not electrical engineering guy (not yet 8-) ).

[exxos]

Yes, I thought about it and heard about term "buffering". But, I don't know how to do it, I'm not electrical engineering guy (not yet 8-) ).

use something like a 74LS244.. drive the LEDS from that and not direct from your signals.

[nokturnal]

Hi, thanks for help. In the end I've invested in proper logic analyser, so design with diodes went straight to trash.

I've managed to make adapter work, here's short sample:



Still I have one thing to correct, which is really baffling. My driver refuses to work after disconnecting logic analyser from an adapter (there's no diodes and I plug directly to lpt signals). With logic analyser plugged in no problem at all. At first I thought that I broke code or something, but no.
Anyone could suggest me what could be a cause and how properly fix it? Check voltage of all signals?

[Steve]

This is very cool, but I am wondering what utility it is on an Atari? Can ScummVM be programmed to use it perhaps?

[nokturnal]

Well, yes driver might be programmed, so audio is replayed from real thing. It behaves like real OPL, so there is possibility to replay VGM formats and D00 for example (,they contain dumps from opl2/3 registers). There's alot of music from different platforms.It doesn't take alot of cpu time.
There is possibility to for example load some presets/instruments and use opl2/3 as instrument. And possibly some more. See for example FM-YAM for c64.

[Cyprian]

Another idea is to use it with Cubase.

[nokturnal]

Little update to my Logic Analyser issue. I've disconnected all LA probes except GND. Disconnecting GND probe causes problem for some reason.

[czietz]

Little update to my Logic Analyser issue. I've disconnected all LA probes except GND. Disconnecting GND probe causes problem for some reason.

If I saw it correctly in your schematic you don't have a separate ground connection in your adapter and connecting the LA adds that ground connection. Removing it breaks the connection. Don't rely solely on the connector shield as ground. Connect (preferably all) ground pins inside the connector