You've likely seen these 4 button keypads on ebay, ali-express, or elsewhere...
Maybe you've also seen them blank. The convenient 0.100 center female plugs have 5 pins, for the 4 buttons and a common. Plug into 4 digital inputs with some usual de-bounce logic, and its very easy to code both single button hits, and at least some useful combinations of multiple buttons pressed together. As a bonus, the button array has a peel-away backing with some very strong adhesive.
The big problem: "1 2 3 4" is just not very instinctive.
So after long consideration, I decided on some better labels for a 4 button array, to make them much more instinctive to use in a variety of projects. With a little imagination and some clues from an LCD screen or serial output, you can hopefully see where these are MUCH more useful for programming settings in a project, which you later can save to EEPROM or other non volatile memory.
So these buttons did not exist! To get them, I had to pay an overseas supplier to have my own graphic custom printed this way at the factory, and I had to commit to buy them in lots of 100. They came out well, and the printing seems very durable to handle a lot of "finger traffic".
Anyway, now I'm hoping to recoup some of the funds I had to spend, as I really don't need (and certainly did not WANT) to buy hundreds! So if you want one, you can paypal me $5 for anywhere in the USA. Of course some of the money goes to postage and paypal fees. So just add another $2 for each additional one you want, up to 5 total. My PAYPAL email address is "r_constan@elfintechnologies.com". You can write me there (or here) with any inquiries too, but please use the contact form on my website for immediate answers. The contact link is at the bottom right of any page.