a simple circuit for a car alarm needed

[Shaun B]

hello all , i have a cone speaker for an alarm with built in siren , im
going to put it into my car as a deterent through the door light switches
( curtisy lights ) but need a circuit that will drive the cone speaker if
the door is opened . it needs to have a 30 second to 1 minute delay so that
i can turn it off with either the key in ignition or a hidden switch.

what would be great would be that when im getting out of my car to lock up i
turn on the alarm with a hidden switch , and when i want in i open the door
and have 30 sec to 1 min to turn off the alarm with the same switch or the
siren goes ( from the door curtisy switch ).....

im also puting in a 4 code keypad lock with a pulse time of 30 seconds to
start the car through a relay, i bought the kit from Talking Electronics PTY
LTD and would like to know if wiring this to the accesories or somewhere
straight to the battery is better , ie if i wire it to the accesories the
timeout function will be lost because all one has to do to reset it is turn
it off and back on with the key. if i wire it to a constant 12 volt supply
im worried that it would drain my battery and need to know the power
consumption for a keypad lock like mine........if you know the one im
talking about thats great if not i cant post a schematic of the circuit
because of copyright and legale stuff . its in the " Smart Security
Devices - Book 1 " at page 20. if no one knows i'll have to ring em up.....


thanks plp

shaun b

 

[Jason James]

Simple alarm costing less than $20

Parts: screamer, about $15,..one driving-light relay (Narda) about $3 or
so,..plus some wire.

Mount a mini-toggle switch externally where it will get the least water
ingress. Then use it to arm your alarm cct by wiring it in series with the
relay-coil which has a screamer connected directly across it (mind which
polarity the screamer wants). The other end of the coil can be triggered by
your door-boot-bonnet etc switches. To make the alarm stay on even if the
doors are shut again, you need to use the relay's 'make-set' contacts
continue to supply the earth or volts (depending on which polarity your car
uses,... XD-Fords use volts (+12v) to switch the courtesy lights) to the
relay effectively 'latching' it on. Cancel the alarm by operating the toggle
switch to 'off' then to 'on' after you have alighted from the car.

If your car uses earth to operate the courtesy lights, the toggle-switch
will be in the volts feed to the relay,...if its volts switched to the
lights,..it'll be in the earth feed. One extra feature by 'design-accident'
is that the courtesy lights come on while the screamer is running. An
isolation diode can be used to stop this if you wish. I use a driving-light
relay which doesn't have suppression diodes across the coil to worry about
coil-polarity.

This alarm didnt stop 1/4 windows being broken or door locks,....so I just
left the driver's door unlocked when the car was parked within earshot. This
alarm has saved the car from theft 4 times.

Jason