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
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
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