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Topic: What is the correct wiring for MIDI out? (Read 205 times) previous topic - next topic


Apr 30, 2017, 08:08 pm Last Edit: May 01, 2017, 10:20 am by vanakaru
There are too many suggestions how to wire MIDI out with Arduino. Which is the ultimate correct one?
Like why there is 220 Ohm resistor on TX in some designs and even 7404 Hex inverter in others?
with 7404
without resistor on TX
However it works either way. So are these thrown in just for kicks?


Depends how picky you want to be. The original MIDI specification, noted as "still acceptable", shows the version with a non-inverting buffer (2x7404) and 220 ohm resistors. The 2014 updated spec. keeps the resistors but makes the buffer (7404 or other) optional and says Pin2 should be connected to ground via 0.1uF capacitor, not directly. See https://www.midi.org/specifications/item/midi-din-electrical-specification

The Instructables version with no pin numbering and no buffer or Tx resistor is plain wrong.



I see.
Seems like the 0.1uF cap is optional if you run long cables.
So 220R resistors on both pin 4&5(to 5V and TX) is the way to go.


You can check with the MIDI people:
To get the latest (2014?) specification you will need to sign up for a free account.

The 1.0 specification uses:
Pin 1: No Connection
Pin 2: Cable shield
Pin 3: No Connection
Pin 4: +5V through 220 Ohm resistor
Pin 5: UART through two inverters and 220 Ohm resistor
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May 02, 2017, 08:54 am Last Edit: May 02, 2017, 08:55 am by vanakaru
This is from 2014 specs.

Pin 2 must be tied to ground on the MIDI transmitter only.
The buffer between the UART transmitter and Rc(220R resistor) is optional and system-dependent.
The optional ferrite beads are 1k-ohm at 100MHz such as MMZ1608Y102BT or similar

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