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I'm designing a MIDI project using these SDS-50J connectors. The datasheet provides a suggested footprint diagram and labels the pins 1 through 5:

DIN-5 pinout

It does not, however, label the bottom-most two pins circled in red. Should I assume that these pins are for mounting only and should be left unconnected, or are they shield pins to be grounded on one end?

EDIT: You can see this pins on the photo, too:

Photo of DIN-5 connector

Also, this table on page 2 of the datasheet may provide a clue:

Materials table from datasheet

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Those two pins are what the datasheet calls "earth pins". They connect to the metal shell of the DIN connector:

MIDI cable
image bv Opersing2688, CC BY-SA 3.0

In general, these DIN-style cables can have five data lines, and the outer shell can be connected to the cable's shield (if it has a shield), in which case it would usually be earthed.

However, with MIDI, there are only two data lines (on pins 4 and 5) that form the current loop, and pin 2 must be connected to the cable shield. In a MIDI cable, neither pins 1 and 3 nor the connector shield are connected to anything.
(For how to handle earthing of pin 2, see the Electrical Specification Update [2014] of the MIDI specification.)

For a MIDI connector, you could leave these pins open. However, ESD tests are done on the connector shell, so you might want to connect it to earth to prevent the ESD from arcing over to any of the data lines.

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Those pins are just a physical anchor for the connector. They have no electrical function. (Although they might make contact with the metal shield of the mating plug, so it might be a good idea to ground them.)

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  • \$\begingroup\$ I think it may vary by connector vendor. The pictured one looks very much like those pins connect to a wiper that will contact the connector shell. Whether or not to connect it to anything in the circuit is a separate question that relates to the earthing of the connector and probably the cable screen and ground loop mitigations etc.. \$\endgroup\$ – KalleMP Apr 11 '18 at 18:26
  • \$\begingroup\$ MIDI signals use current loops and optocouplers, grounding is not necessary (and can even be detrimental due to ground loops) \$\endgroup\$ – TEMLIB Apr 11 '18 at 18:28
  • \$\begingroup\$ @KalleMP I doubt they constitute a switch. If you take a look at the manufacturer's website it lists 0 for 'Internal Switch(es)' for this part. \$\endgroup\$ – calcium3000 Apr 11 '18 at 18:41
  • \$\begingroup\$ @calcium3000 I was not thinking of switch contacts but earthing contacts. There are very few connectors besides circular jacks and barrel connectors that I have seen with insertion switches (figure 8 mains sockets are the other type I have seen). \$\endgroup\$ – KalleMP Apr 11 '18 at 18:48
  • \$\begingroup\$ @TEMLIB With MIDI grounding may be counterindicated but the connector is a DIN connector first and a MIDI connector second. The function of those solder pins is not designed for MIDI only. \$\endgroup\$ – KalleMP Apr 11 '18 at 18:50

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