Two Simple Relay Based Motorcycle Alarms

Two Simple Relay Based Motorcycle Alarms

Circuit Description

These are two – easy to build – relay-based alarms. You can use them
to protect your motorcycle – but they have many more applications. If
you use relays with 6-volt coils – they’ll protect your “Classic Bike”.
Both alarms are very small. The completed boards occupy about half a
cubic-inch – 8 cc. The standby current is zero – so they won’t drain
your battery.

Circuit No.5

Circuit Number Five uses a SPCO/SPDT relay – but you really only need
to use a SPST relay. If you are going to use the veroboard layout
provided – you’ll need to use the style of relay specified. But you can
build the alarm using whatever style of relay you have available.

Two Simple Relay Based Motorcycle Alarms

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. When one of the trigger-switches is closed – the relay will
energize and the siren will sound.

You can choose what happens next. If you build the circuit as shown,
the siren will continue to sound until you turn it off – or until the
battery is exhausted. But, if you leave out D3 – the siren will stop
sounding immediately the trigger-switch is re-opened.

While you’re within earshot of your machine – the former
configuration is best. You can always turn off the alarm yourself. But
if you are going to be away from your bike for any length of time – and
you don’t want to cause a nuisance – then the latter configuration is
probably more suitable. If you include a SPST switch in series with D3 –
you can select the behaviour that best suits the circumstances at any
given time.

Two Simple Relay Based Motorcycle Alarms

Relay coils and some sounders produce high reverse-voltage spikes
that will destroy sensitive electronic components. D1 and D2 are there
to short-circuit these spikes before they can do any damage. Although
there is nothing in the alarm circuit itself that could be damaged – I
have no idea what other electronic equipment might be connected to the
same power supply. So I included the two diodes as a precaution. If
you’re satisfied that there’s nothing on your bike that might be damaged
in this way – you can leave out the two diodes.

Circuit No.6

Circuit Number Six uses a DPCO/DPDT relay – but you really only need
to use a DPST relay. If you are going to use the veroboard layout
provided – you’ll need to use the style of relay specified. But you can
build the alarm using whatever style of relay you have available.

Two Simple Relay Based Motorcycle Alarms

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. When one of the trigger-switches is closed – the relay will
energize and the siren will sound.

You can choose what happens next. If you build the circuit as shown,
the siren will continue to sound until you turn it off – or until the
battery is exhausted. But, if you leave out the (yellow) solder-bridge
in the top left-hand corner of the diagram – the siren will stop
sounding immediately the trigger-switch is re-opened.

While you’re within earshot of your machine – the former
configuration is best. You can always turn off the alarm yourself. But
if you are going to be away from your bike for any length of time – and
you don’t want to cause a nuisance – then the latter configuration is
probably more suitable. Connect a SPST switch in place of the (yellow)
solder-bridge – and you can select the behaviour that best suits the
circumstances at any given time.

Two Simple Relay Based Motorcycle Alarms

Relay coils and some sounders produce high reverse-voltage spikes
that will destroy sensitive electronic components. D1 and D2 are there
to short-circuit these spikes before they can do any damage. Although
there is nothing in the alarm circuit itself that could be damaged – I
have no idea what other electronic equipment might be connected to the
same power supply. So I included the two diodes as a precaution. If
you’re satisfied that there’s nothing on your bike that might be damaged
in this way – you can leave out the two diodes.

General Points

Whichever alarm you build – the circuit board and switches must be
protected from the elements. Dampness or condensation will cause damage.
Without the 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 as close as possible to the power source. This
is Very Important. The fuse is there to protect the wiring – not the
circuit board. 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’s energized while the ignition is on.
Then every time you turn the ignition off – the alarm will set itself.

When the alarms are not sounding – the circuits use no current. This
should make them useful in other circumstances – where a power supply is
not readily available. Powered by dry batteries – with the relay and
siren voltages chosen to suit – the alarms could be fitted almost
anywhere.

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