by psychobilly » Thu Jul 24, 2008 6:50 pm
Loop alarms are like the ones used in shops to stop you walking away with the items on show... well make a load of noise if you try.
B&Q do a Friedland shed alarm kit for £10.98 which gives 15s exit and entry delay before the alarm sounds - I use one on the observatory.
The 15s delay is a bit long for a loop alarm so a bit of scoping around the circuit shows that by adding a 680k resistor across R3 and R7 you now have delays of no more than a second or so, I replaced the door contacts with a loop made from a 3.5mm mono extension lead - cut the lead in half, shorted both conductors of each half together and soldered them to the "contacts" pads on the PCB.
The very loud sounder was mounted to the top of the case witht he wiring being shortened and soldered to the "siren" pads on the pcb...
The loop can be extended by adding additional 3.5mm extension leads to the "circuit".
When im setting up outside and and walking back and fore to the house I can now easily "protect" the kit in the observatory by "looping" it all together with the Alarm [:D]
Would be ideal for scopes/tripods etc left outside while you pop in for a cuppa...
[image]http://www.btinternet.com/~psmithuk/stuff/scopealarm.jpg[/image]
Billy..