borfo Posted April 26, 2014 Report Share Posted April 26, 2014 Will 6n137s work in the core lpc17 module instead of the 6n138s? If so, Which resistors would I have to change? Quote Link to comment Share on other sites More sharing options...
Marxon Posted April 26, 2014 Report Share Posted April 26, 2014 Hi borfo, yes the 6N137 should work. I would try it with a 10k instead a 1k pull up resistor. It is connected between pin 6 and VCC. (R18 and R23). Best regards Marxon Quote Link to comment Share on other sites More sharing options...
borfo Posted April 27, 2014 Author Report Share Posted April 27, 2014 Cool. That seems to be working. Thanks. Quote Link to comment Share on other sites More sharing options...
kpete Posted April 27, 2014 Report Share Posted April 27, 2014 (edited) In looking at the Fairchild 6N137 specification, it indicates that the ENABLE line should be left open or pulled up above 2 volts. The LPC17 schematic shows a resistor on this pin that is connected to ground. Might be best to cut and remove the resistors connected to pin 7 of the 6N137's. The output pin 6 is also specified to output a low voltage value of 0.6v at 5ma so the 1k ohm resistor between pin 6 and the +5v should be OK. I used the specification at this link: https://www.fairchildsemi.com/ds/6N/6N137.pdf Edited April 27, 2014 by kpete Quote Link to comment Share on other sites More sharing options...
Marxon Posted April 27, 2014 Report Share Posted April 27, 2014 (edited) Kpete's answer is more sophisticated, now i am embarassed by my one which seems to be wrong. Sorry for that. Sometimes i am too rash :) Edited April 27, 2014 by Marxon Quote Link to comment Share on other sites More sharing options...
borfo Posted April 27, 2014 Author Report Share Posted April 27, 2014 Ok - thanks guys. I cut out r24 and r19, and replaced r18 and r23 with 10ks. I'll try it out like that and see if I need to switch back to the 1ks on r18 and r23. Quote Link to comment Share on other sites More sharing options...
kpete Posted April 27, 2014 Report Share Posted April 27, 2014 Working and working reliably are 2 different things and can cause problems in the future. I wasn't familiar with this part so I pulled up the specification. I also thought that the LPC17 was using 3.3v rather than the 5v for the receivers but looking at the schematic showed I was wrong. The 10k for the pull up might work but it will increase the turn-off characteristics of the part. On page 6 of the specification on figure 10 it shows the part using 3 resistor values, the highest being 4k ohm. It shows a propagation delay of ~100ns with the 4k load and only ~50ns with a 1k load. I don't know if this would cause problems with long Midi cables or not but I would go back to the 1k resistor value anyway. In fact you could just add (parallel) a 1k ohm resistor to your 10k that you changed. Pete Quote Link to comment Share on other sites More sharing options...
borfo Posted April 27, 2014 Author Report Share Posted April 27, 2014 Cool - I'll switch them back to 1ks, that's easy enough to do. Thanks a lot for the detailed answers guys. Very much appreciated. Quote Link to comment Share on other sites More sharing options...
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