Only the 3rd cct fits into that category.

pressing a switch connect 2 unique resistors in series to a cap. The IO pin can time the charge/discharge rate of the cap by switching between output (to provide current) & input (to monitor voltage). There's a function in Proton+ picbasic called 'pot' (I think) that will do this for you.

If you wanted to make the code easier, in addition to allowing a simple wake up on key press, an IO pin would also be connected directly to the capacitor.

 

I was looking at the page in portrait layout and so I was counting the first (left) as the third (bottom). Now I've turned it around the one that's interesting is the first one. That diagram will work without using the internal pullups and so solves the lack of pullups on the newer pic chips. I may have a play with this tomorrow just to make sure it works as I envisage. Assuming it does a programmable combination lock with one of the 8 pin pic chips should be doable.

Will you be watching "State of Origin" tonight?

Mike.

 

Nah, sounds too much like sport