Another way to drive a 16 way matrix keyboard is the inexpensive PCF8574 and PCF8574T I2C expander boards.
I have a couple of these but not made time to try them out yet.
There is however, a lot to be said for the simplicity of the analogue solution and the Robodyn module mentioned by
Mike ZL1AXG looks very practical particularly their transparent button top cap to protect the printed key legend.
73 Bob GM4CID