Optically isolated DMX issue

S

SteveCS

Well-known member
I have made this optically isolated DMX board. But, I want to use it with a Teensy 3.2
Doesn't appear to work, yet I have tested all the board and all seems to be operating correctly (Opto isolators etc).

Would it be that the 3.3v outputs of the Teensy are not enough to drive the circuit? Maybe the 470R opto-isolator resistors need lowering?

http://www.mathertel.de/Arduino/DMXShield.aspx

Any advice would be great
Thanks

DMXShieldSchema.png
 
I dropped the opto isolator resistors to 82R (R4 and R6 - transmit and direction). DMX light randomly flashes occasionally. Something still screwy
 
Hmm. Doesn't show pin 7 of the opto isolators connected in the schematic or in the 6n137 datasheet.
I have built this circuit before on an UNO and it worked. I could try it I suppose
 
Well, I have to admit defeat. I think this may be a timing issue or software related, as I have changed out all the components again, and tested again, and all seems fine.
I have read the readme file for the TeensyDMX.h library, but it's as clear as mud if you don't know the concept of how it all works.

Hmm
 
In that DMX circuit diagram, there is a 4k7 pullup on the exit of the opto-coupler. Is it possible that the output signal cannot overcome that pullup?
I dropped the input resistor to a 100R (maybe that was too low?). I don't actually think the signal is passing through the opto-couplers
 
Wrt R7, use 220R here, + end to 3.3v for Teensy LC - 4.1 Midi. Note that 6N137 output is inverted wrt 6N138/9.
 
AAAHHHH....

That schematic is wrong. Pin 2 on the output is pin 3 on a DMX lead and vice-versa
Swapped them around and now it works (with dmxTx.setRefreshRate set to 20)
 
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