optoisolator woes

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Mar 26, 2008, 8:07:29 PM3/26/08
to pushpin
Hello everyone,
I have been trying to build an interface for pushpin, with no success
at all. I bought three 6n138's from digikey, and 1k, 200, and 5k6
resistors as well as a 4.7uF electrolytic capacitor from my local
RatShack. I have read all postings to this group as well as ove's
four pushpin-relevant blogposts:

btw, p=99 isn't tagged with pushpin. The other three are.

I have the japanese version; CGB-JPN-1; it was bought for me when I
was a child, and was sitting in my drawer unused for years until I
heard about LSDj. Since then I have performed the "pro sound" mod on
it. I doubt any of that matters but it never hurts to be thorough.

I have scrutinized bost Bill Byrne's working breadboarded interface
and ove's schematic.

To me it seems like they differ slightly. First off, on pin 2 in
Bill's circuit, it looks like the 200ohm resistor isn't actually
connected. Correct me if I'm wrong, as I may be, but wouldn't wiring
it up like he did just short the leads as that horizontal strip is
just one piece of metal? Wouldn't this make the resistor useless?
Next I noticed that pin 6 of the 6n138 is grounded. Ove's schematic
doesn't show this. Should I ground pin 6 or not?

I also noticed that Vcc and Gnd in bill's circuit are going up, yet SD
is going down; this implies he isn't using the GB to power the
optoisolator. Is that important? Currently I am using Vcc of the
GBC, which my meter says is 4.94v. Am I being silly or is that okay?

Finally, I am using a midi cable that I cut in half, as I don't have
any spare midi jacks. Looking at the male end, from left to right,
pinouts.ru tells me that it's 3,5,2,4,1. It also says that pin 4 is
current source and pin 5 is current sink, so it seems to fit the
schematic. Looking at pinouts.ru's MidiOut pinout, it is just
horizontally flipped, so I'm thinking I have this right. If someone
could confirm that for me I would appreciate it :)

I have been using ove's sdtest program, and I cannot get *anything*
out of it. If I connect SD to the GB's ground it reads it just fine.
If I connect SD, Vcc, and Gnd of my keyboard (an M-Audio Ozone; though
I have also tried a Korg Electribe-R MKII and a MOTU Fastlane USB) I
get timing and events in sdtest just fine, but only a few, random
notes in pushpin, as ove described.

I have tried all 3 6n138s, hoping that maybe I just fried one, but
nope, none of them did anything.

I tried omitting the 220, I have tried using 1k for R1 and R2 as
someone else with a CGB-JPN-1 described, I have tried with and without
the capacitor, and nothing has worked. I am planning on getting two
10k pots to use for R1 and R2 tomorrow, if I can find the time.

I would *love* to have a midi-capable gameboy, and any hints as to why
my interface is failing so miserably would be highly appreciated.
Many thanks to all who have contributed to this wonderful project :)


Patrick Leonard

Mar 26, 2008, 8:30:56 PM3/26/08
to pus...@googlegroups.com
I posted a schematic awhile back which worked for me. Make sure that
you have you midi wires right since you cut it. I think radioshack has
5 pin dins that you could use for a midi connection. also want to make
sure that you have the game boy wired right. You do need to power and
ground the opto from the game boy. When using pushpin you must press
start before anything happens. Select the midi channel setup from
pushpin's menu, press start and the screen shows 4 rows of 0 00, or
something similar, this is when pushpin will power the opto and allow
midi to come in. A side note is that pushpin only likes it own midi
connection. If you have and other channels playing through it will act

Patrick Leonard

Mar 26, 2008, 9:13:47 PM3/26/08
to pus...@googlegroups.com
Make sure that you ground to pin 5.

I just pulled my breadboard out and hooked it up and it going.

Patrick Leonard

Mar 26, 2008, 9:16:02 PM3/26/08
to pus...@googlegroups.com
one more thought, make sure that your batteries are good.


Mar 26, 2008, 9:31:47 PM3/26/08
to pushpin
It works!

I found your schematic, with the inverter, and I looked at it, it made
more sense than ove's. I looked at bill byrne's again, and saw that
it looked like your schematic with the inverter removed. I built his
exactly the same, except I used a 1k for R1 and he used a 1k2. I will
try to post a picture and possible a schematic tomorrow.

Thanks for the help!

Patrick Leonard

Mar 26, 2008, 9:59:57 PM3/26/08
to pus...@googlegroups.com
Since you got it working could you do a couple tests. Run pushpin on
midi 1-4 and send another track of data on anything above 5. What do
you hear? When starting fresh does track 1 sound different then track 2?


Apr 6, 2008, 10:36:06 PM4/6/08
to pus...@googlegroups.com
I'd love too, except that I stepped on my interface the day after I made it and it hasn't worked since.  I've tried rebuilding it with new parts but no luck yet...


Apr 8, 2008, 10:47:13 PM4/8/08
to pus...@googlegroups.com
Well I managed to rebuild it, I used 1k for R1&R2, 4uF for C1, no inverter... though I have some on hand so I might add it in later.  Looks exactly like  http://gameboygenius.8bitcollective.com/images/pushpin/pushpin-midi-gameboy-2.png
the only change is that pin 5 is grounded.
I have just tested channels 1-4, and a few CCs.  I'll report more when I test it.
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