On 18/04/2019 19:47, Rob Morley wrote:
On Thu, 18 Apr 2019 17:32:32 +0100
Harry Bloomfield wrote:

Ideally, I could do with a better way to be sure at a glance, that
the clutch isn't slipping and the deck is being driven round. One
idea I have is a magnet fixed to the edge of a pulley, rotating past
a coil powering an LED mounted on the tractors dash. Has anyone any
other suggestions?

Bicycle computers use a magnet and a reed switch to measure rotation,
but your mower will probably be going too fast for it to cope. An
Arduino with a Hall sensor could count your spinning magnet revolutions,
and is obviously a lot more configurable but with the overhead of having
to build the system from scratch.


A hall effect switch or reed switch could still give a false reading if
the blade stops exactly in the position where the magnet is next to the
hall effect or reed switch.

The coil would only react to changes so if the magnet doesn't move there
will be no output from the coil irrespective of where the magnet ends up
in the blade stalled position. However what is the on/off ratio going to
be? Unless the magnet energises the coil (or switch) for a substantial
time then the LED may only have a just perceivable flicker which cannot
be seen in daylight. You probably need some simple circuit, say, where
the output from the coil charges up a capacitor which in turn allows the
LED to remain on long enough to be seen at full brightness.

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