Such an application could be a kitchen timer.
How to protect keys against splash/dust/dirt? Keep them inside the box, but then mechanical actions will not work. I came up with these possible alternatives to a membrane matrix keyboard:
- capacitive sensors
- hall effect (need a "magnetic" pen/tool)
- photoresistors (only if the case is transparent)
Something must be wrong in my ideas. So far I came up with these cons:
- capacitive sensors are unreliable, sensitive to static/noise, ...
- hall is power hungry in large deployments, at 5 mA standby for each sensor (but a single row/column could be scanned)
- LDRs need transparent case, a ligthed environment and are somewhat slow to react, in the order of 10 milliseconds
I am about to buy a bunch of LDRs and Hall sensors to test it out...