I was looking for an external contact, to be used with Littlebit circuits instead of the I3 pushbutton.
After some experiments with the protobit I tried a reed switch and it worked !
I will share the outcome of my experiment with this reed switch.
It could be used to detect the position of a stepper motor (see the forum topic from @chris101.
Or a secret chess board contact as @Eidrog is thinking of…
What is a reed contact ?
A reed contact is a little glass tube with a contact inside that can be closed and opened with an external magnetic field.
I connected this reed contact to the proto bit, using the same circuit as used for the I3 button.
With this magnetic contact a lot of inputs can be realised in Littlebit projects.
See also the YouTube video: https://www.youtube.com/watch?v=51rLlwiCzfI