[sdiy] EFM MIDI-Gate?

[Jerry Gray-Eskue]

Ok, If you always have 5 volts on pin 6 the PIC must be supplying the pull
up (as Grant mentioned).
BTW the 10k is a bias resistor and works well with a 270 Ohm pull-up.

My best guess is that you are not getting a good current loop on the input
side, or the connection is reversed.
Pin 2 of the 6n138 should go thru the 220 resistor and to pin 4 of a MIDI
female (panel) connector.
Pin 3 goes to pin 5 of the midi connector. NOTE: the pin out numbers of the
MIDI connector are not in sequence, 4 and 5 are not next to each other.
You may be able to check the loop by removing the 6n138 and put an LED in
the socket pin 2 Anode pin 3 Cathode. It may not be very bright but should
flash when data is received.



-----Original Message-----
From: chromatest at gmail.com [mailto:chromatest at gmail.com]On Behalf Of
Chromatest J. Pantsmaker
Sent: Wednesday, February 24, 2010 7:31 PM
To: Jerry Gray-Eskue
Cc: Synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] EFM MIDI-Gate?


Ah.. sorry, that was old information and was indeed a problem with the
scope.  I'm using a really nice scope now and I still can't get the
circuit to work.

It seems that I'm not getting any output on the 6n138.  I just get 5V
and it doesn't appear to be pulsing or anything like that.  I've
compared the schematic with the traces, and everything goes where it's
supposed to.

On Wed, Feb 24, 2010 at 6:22 PM, Jerry Gray-Eskue <jerryge at cableone.net>
wrote:
>  Pins 5, 6, 7, and 8 all show the same
>> waveform which doesn't seem right to me at all.
>
> According to the schematic You should have +5v on 8 and Ground on 5.
> Check your power supply, and be suspicious of your o-scope software, as
> several people recently pointed out the sound card inputs are usually AC
> coupled and so cannot see DC voltages.
>
> Use a Voltmeter or DVM (if you have one) to check out the DC voltages.
>
> Also the Input side of the opto should have a floating ground relative to
> the rest of the circuit.
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Chromatest J.
> Pantsmaker
> Sent: Wednesday, February 24, 2010 5:52 PM
> To: Dave Kendall
> Cc: Synth DIY
> Subject: Re: [sdiy] EFM MIDI-Gate?
>
>
> I'm still working on this thing, haven't figured out what's wrong yet.
>
> I bought a stack of 10 6n138 optocouplers from mouser.  I've tried
> several now with the same results each time.  I'm wearing a ground
> strap.
>
> So, using the scope, I'm seeing 5V data bouncing on the inputs of the
> 6n138 (pins 2 and 3) but on the output, I'm just getting a slightly
> fuzzy +V and the scope says that it's detecting DC voltage on that
> pin.
>
> I've pulled out every other IC (all socketed) and the results are the
same.
>
> Thoughts?
>
> The Schematic is here:
> http://chromatest.net/EFMmidi-gate.pdf
>