"Mathew Newton" wrote in message
...
Let me explain... (and no, an angle grinder won't do)

Based on the operation of my automated cat feeder (http://
www.newtonnet.co.uk/catfeeder) I've been asked to develop a similar
device for dispensing nuts to birds. The existing design will be
modified slightly to reduce the amount of nuts dispensed in any one
'serving' however its basic principle will remain the same: a motor
will slowly turn a paddle and provide six servings per revolution.

What I want to do is be able to do is trigger only a single serving
and, given the somewhat inexact method by which this paddle delivery
method operates,


????

What's wrong with a simple micro switch that stops the motor when the paddle
blade is there.
A momentary operating switch then bypasses the micro switch to start the
paddle turning.
The micro switch closes when the paddle blade moves and opens again when the
next paddle blade pushes it.