Hey guys. I'm currently starting a school project which will do the following but have a few things I need to sort out, and I hope you are the one's who can help .

It will be a device that will dispense an insulin pen when a button is pressed. When the button is pressed the next time, a different pen will be given. Then the next time pen 1 will come back. This is because diabetics generally take a range of insulin and this machine will ensure the correct one is taken blah blah.

A simple diagram is here:



The problems I have are:

1. What kind of mechanism could be used to make the drawer type things slide/fall down.

2. What kind of circuit could alternate between the two drawers (plz dont just post alternating or something stupid like that)

Cheers

BTW I have a knowledge of electronics from studying it at GCSE so can understand some terms etc. however less familiar ones may need to be explained in details.

Thanks again,
Dave