Whilst working as a consultant for a computer products company I was asked to draw up plans for a switch which could be operated at different forces. The design I came up with utilise the large top button which can be rotated and whilst rotating it moved the fulcrum of a spring along its length thus changing the force needed to operate a micro switch to complete the circuit. I was awarded the patent for this job and picture of the unit is below.
Derek's dabblings 