PlanetCatfish.com

for my Yr10 project, we have to make something with a little cicruit, and i thought my tank would give me answers, so my plan is

a dryness sensor, so when the water drops to a level below the wires, an LED flashes, and tells me a water change is needed
now, for a 9V battery, would i need to attach a small rubber box with holes in to monitor water depth without passing currents through the whole body of water?

I would attempt to make a mechanical fixture where you use a float (similar to how the float in a toilet cistern works) to make the contact with a micro-switch (or similar). This way, there will be no chance of electricity making contact with the water.

Of course, the SENSIBLE thing would be to build a (cheap) nitrate meter, and measure nitrate levels, rather than water level, as the evaporation out of the tank is not a good measure of when you need to change water.

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Mats

Darn, the teacher says i have to make a crappy alarm system, like a trip wire, or pressure pads

What's the difference between a trip-wire alarm and a water-level alarm? I mean it's certainly something that could be useful, even if it's not necessarily useful for showing when you need to change water...

Essentially, it would do the same thing as a pressure pad, except that it uses a float to indicate water level, and if it goes below (or maybe better, above) it gives off a signal. [Above level signal would be useful if you fill the tank from a hose or similar, to indicate when you need to turn the hose off...]

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Mats

How about a Temperature Controller. As in controlled plug to plug your heater into.