Below is my Arduino based CW iambic keyer.  I wanted to be able to change my WPM on the fly using a potentiometer.

I had some LED 7 segment displays that would be perfect for this application.  The issue then becomes how do I not use up all of my IOs…   Below is the IC that I used.

Microchip Technology MCP23017-E/SP

This IC is much cheaper than a multiplexing IC for 8 digits.

Now I have plenty of IOs left over for buttons to Call CQ,  give my callsign, and QTH etc.

If I wanted, I can keep adding more ICs (up to 8 total or 128 IOs!!) as needed just as long as I set a new unique address to each IC when using I2C.

I have also used this IC with an LCD display that uses up IOs quickly.

73,

Mike, AB1YK