On Thu, 22 Jul 2004 14:02:46 +0000 (UTC), "Lawrence Zarb"
wrote:

Harry,

It will be used to connect to a water alarm circuit which in turn is
connected to a water solenoid.
When I do my 20% water changes I have plumbed in a system that, via
carbon/water filters will fill up the tank directly from the mains by
opening a stopcock. the solenoid is there to stop the water when it
reaches a certain level (governed by the height of the rods) which shut
the water off, just in case I forget to turn the tap off. This is
because the water flow will be quite slow and it will take some time and
I donot want to be wating for the tank to fill up..

One important point, Lawrence, is to make sure that one side of the
alarm sensor is connected to earth. Provided that you then have a
very high impedance sensor input on the alarm circuit, it won't be a
problem for the fish.

Another option, which I have used is to use a plastic float switch
fitted to a plastic bracket. These are almost as accurate as
contact arrangements and have the advantage that there are no metallic
items in contact with the water at all.

RS Components part number 228-1986 is suitable and pretty cheap.
I've recently used one of these in a water container which has a pump
to provide misting for my snake vivarium. I wanted an arrangement
that would stop the pump running if the container water level falls
too low - I don't want the pump running dry. THe pump is normally
turned on by a humidity sensor in the vivarium, but if the container
water level is too low a beeper sounds instead to remind me to fill
the container.

This application is not vastly different to yours in terms of what is
needed,




..andy

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