Jeopardy buzzer controller

KiCad project

Pictures of the PCB:

Only eight buzzers are supported and the Arduino has twelve digital I/O pins, so no matrix circuit is needed.

Schematic screenshots

Here are screenshots of the schematic so you don't need to download / install / launch KiCad:

XLR connector

They are Neutrik NC4MBV which are:

4 pole male XLR receptacle, grounding: separate ground contact to mating connector shell and front panel.

Each connector has four cylindrical pins with shoulders. A rectangular tab on the bottom contacts the shell of the mating connector.

KiCad comes with symbols & footprints for 4-pin XLR connectors; I modified both slightly.

Symbol

I added a ground pin to the "XLR4" symbol in the KiCad Connector library:

Footprint

I started with the "Jack_XLR_Neutrik_NC4MBV_Vertical" footprint in the KiCad Connector_Audio library, which exactly matches the footprint provided by Neutrik.

After the PCB was fabricated, I saw that those dimensions hold the connector about ¼ inch (6 mm) above the board. The shoulders of the cylindrical pins and the square section of the ground tab both rest on the PCB surface. I think this looks sort of silly and expected the black plastic housing to touch the board.

To see a comparison, I drilled out the pads on an extra board. In the pictures below, the original footprint is on the left and the footprint with drilled-out holes is on the right:

I edited the footprint to make the black plastic housing touch the PCB. First I increased the sizes of pads 1-4 so the full diameter of the cylinder could go through the board. Then I changed the ground pin from a circle to a slot to let the bigger non-square part of the ground tab go through as well.

But I never got a board fabricated with the modified footprint! When assembling the PCB into the enclosure, I discovered that having the connectors on long legs was actually very helpful because they could bend slightly to accommodate imperfect hole alignment in the plastic wall.