Either will work.. 10 Ohm and 33 Ohm are the official MIDI spec but I think Paul posted 47 Ohm for both before that spec was available.
I suspected it... asked just to be sure.I would not recommend following the advice from that blog. There is very little difference between using two 47 ohm resistors versus 10 and 33 ohms. But using 220 and running the transmit pin directly to the cable without any resistor is not good. 5.6K for the pullup is also not good advice. These may work some times, but they are far outside the recommended range.
I'm not sure what spec you're referring to for the diode but it's just there for a bit of polarity protection so I think that's OK.
I've tested both Midi spec for 3.3v (10 and 33 ohm) and Paul's recommendation and both work well in my devices.
I've struggled a lot until discovering my volca beats receive Midi In well only if batteries are charged above 40%.
Hope it helps somebody else.
PS: this picutre has one resistor missing, as @oddson noted and I'll post an updated picture of the protoboard for reference
If you're using Teensy 3.2 (as you mentioned in message #3), you could also just connect the pullup resistor to +5V. The digital pins on Teensy 3.2 and 3.5 are 5V tolerant, so it's ok to give them a 5V signal.
But do not try that with Teensy LC or 3.6. Those are not 5V tolerant. Applying more than 3.3V to the pin could damage them.
So I am thinking about using this midi IO board from the MIDIbox.org universe with a T3.2:
http://www.ucapps.de/mbhp/mbhp_midi_io.pdf
I plan to change the Out R's to 47 Ohms and tie them to 3.3V as per the standard but will power the Rx with 5V. This board is designed for an STM32 uC which is 3.3V( 5V tol.) also, but I'm wondering how it might be able to power the Outs with 5V. Is it a matter of the pin handling, just toggling between Float and Sink on the Tx pin? Is the Teensey using push-pull on the UART Tx pin?
Yogi
Why 5v ? 3.3v is ok for midi output.
Daniele.
I think it will work either way for 5 volt tolerant systems but there does not seem to be anything on that board that needs a 5 volt supply. I think that's Daniele's point.
Was thinking the 6n138s are 5V devices, could be wrong. If they can operate at 3.3V then wouldn't I have to change all the R values?
Yogi
Just finished building it up this afternoon, and yes the two Midi IN channels are @ 5V and the two Midi OUTs are setup for 3.3V (just a minor hack as outlined above). With only 3 UARTs on the T3, there are two un-used conductors on the cable so getting 3.3V to the board was easy enough. It should be good on the T3.2, just trying to figure out how the Tx pins are setup, push-pull or open drain.Right, 5v. So you need 5v for the input part. Not sure about the output.. Do you already have that board ?
Daniele.
This is from the data sheet... but logic gate based stuff may need 5v...data sheet said:OUTPUT
Supply and output voltage
6N138
VCC, VO-0.5 to 7V