DESCRIPTION:
I have built a little circuit board that can connect to the keypad connectors of a cheap pocket calculator to simulate keypresses. I use this board together with a custom Arduino library so that the calculator can act as LCD to display a given number. Not a very smart idea but a quick hack when you need a LCD for just one number.

Used for this project:
https://hackaday.io/project/12756-a-feature-rich-arduino-waveform-generator

Arduino library available for download on the hackaday page.