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Aquarium Temperature Alarm

Don't let your tropical fish freeze or fry to death. This programmable circuit warns of out-of-range temperature conditions

By Peter Smith

It’s common knowledge that the water in a tropical fish tank must be maintained within a relatively narrow temperature band – typically around 24°C. In most small home aquariums, this is achieved using a thermostatic heater. When the temperature drops below a preset level, the heater switches on and when it rises above a higher preset, it switches off.

Most aquariums are also equipped with a permanently installed thermometer, allowing the operation of the heating system to be checked at a glance. And that’s basically it – nothing more elaborate than this is required while everything is working normally.

But consider the outcome if the heater were to fail due to an open-circuit element, stuck thermostat or extended mains power failure. If a problem like this occurred at an inopportune time such as when you are away on holidays, would the failure go unnoticed by others in the household? And even if you were there, would you detect the problem soon enough to take remedial action?

This is where the Aquarium Temperature Alarm comes in. When the water temperature falls outside a predetermined range, a raucous two-tone alarm sounds to alert anyone in the vicinity of the problem.

Need more noise? That’s not a problem either, as we’ve made provision for triggering an external alarm system via an optional open-collector output. This could be wired to one sector of a house alarm, which could also power the Aquarium Temperature Alarm for continued monitoring during a mains power failure.

Alternatively, the output could be wired to our SMS Controller project (see the October & November 2004 issues) and/or the PICAXE NetServer (described in this issue) for alerting and monitoring worldwide!

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