MIDI-Thru problem ?

[Trevor Page]

Hi Michael,

You might like to try playing around with the emitter resistor connected to the optocoupler. I use a 2K2 when using the CNY-3 optocoupler. I find this value to be pretty critical for good performance. The value of this resistor will to some extent determine the switching times for the phototransistor. The CPU/UART might well work ok but other equipment connected via the thru port will not.

Trev





----- Original Message -----
From: Michael Buchstaller <buchi at takeonetech.de>
To: synth-diy at node12b53.a2000.nl
Sent: Thu, 23 Nov 2000 09:07:27 +0000 (GMT)
Subject: MIDI-Thru problem ?

> Hello dear listmembers,
> 
> i am again here to pest you with my silly questions:
> 
> After some struggling with various embedded processors and much
> help from you, i finally mamaged to biuld my first DIY MIDI device, a simple
> MIDI note --> 16 Gates converter box.
> It just works fine, but then i wanted to add a MIDI-Thru jack. So i looked at the
> MIDI.org schematic at http://www.midi.org/images/midihw.gif
> and added the output according to this.
> My circuit ist here: http://www.takeonetech.de/midi.gif
> 
> OK, the inputs to my onboard CPU does work and recognizes all MIDI data
> without problems, so i do think that there is no problem in the input stage - the
> signals do also look fine when i look at them with a scope.
> 
> But MIDI gear hooked up at the MIDI-Thru connector receives only garbage
> and erroneous data. After double-checking all parts, connectors and cables
> and verifying that the data at the thru-connector looks to me absolutely the same
> as the on as then in-connector, i am absolutely clueless.
> 
> Has anybody encountered such a problem yet ?
> 
> 
> -Michael Buchstaller




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