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Circuits
Any number of normally open switches may
be used. Fit the mercury switches so that they close
when the steering is moved or when the bike is lifted
off its side-stand or pushed forward off its
centre-stand. Use micro-switches to protect removable
panels and the lids of panniers etc. While at least one
switch remains closed, the siren will sound. About two
minutes after the switches have been opened again, the
alarm will reset. How long it takes to switch off
depends on the characteristics of the actual components
used. But, up to a point, you can adjust the time to
suit your requirements by changing the value of C1.
The circuit board and switches must be protected from
the elements. Dampness or condensation will cause
malfunction. Without its terminal blocks, the board is
small. Ideally, you should try to find a siren with
enough spare space inside to accommodate it. Fit a 1-amp
in-line fuse close to the power source. This protects
the wiring. Instead of using a key-switch you can use a
hidden switch; or you could use the normally closed
contacts of a small relay. Wire the relay coil so that
it is energized while the ignition is on. Then every
time you turn the ignition off, the alarm will set
itself.
When it's not sounding, the circuit uses virtually no
current. This should make it useful in other
circumstances. For example, powered by dry batteries and
with the relay and siren voltages to suit, it could be
fitted inside a computer or anything else that's in
danger of being picked up and carried away. The low
standby current and automatic reset means that for this
sort of application an external on/off switch may not be
necessary. |
