Dretful mcp23017- Q2W board_addon
a board that plugs into the quick2wire MCP23017 board for bounce free connection of up to 8 reed switches. only uses port A, port b can be omitted or passed through with a long header. BOM: 2 resistor arrays, one parallel (330R) one serial (2K7), 8 off 470nF capacitors, 1 10K resistor and 3 1N4004 diodes or similar. Header for port A soldered long end down. 2 headers (female, male as you please) to plug the switches into. 8 common across the top, if you need them all, and 8 switched down the middle. Use a 5v supply. Screw holes should fit the Q2W expander exactly. Circuit details inspired by this post: https://www.raspberrypi.org/forums/viewtopic.php?t=194415, particularly pcmanbob.