Posts Tagged ‘home security alarm’

Single Zone Digital CMOS Alarm

Circuit :Ron J
Email Ron

Description:
This circuit features automatic Exit/Entry delays, timed Bell Cut-off and System Reset. It has provision for normally open and normally closed switches and will accommodate the usual input devices such as Foil Tape, Pressure Mats, Magnetic Reed Contacts, Passive Infrared Detectors and Inertia (Shock) Sensors.

Notes:
The green Led should be lighting before you set the alarm. When you open SW1 The red Led will light and the Exit delay will begin. You have about 30 to 40 seconds to leave the building. As you do so the buzzer will sound. It should stop sounding when you close the door behind you; indicating that the trigger circuit has been successfully restored within the time allowed. On returning, when you open the door the buzzer will sound again. You then have about 30 to 40 seconds to move SW1 to the “off” position. If you fail to do so, the siren will sound. After about 15 to 20 minutes, when the relay drops out, the alarm will attempt a Reset by using Q3 to switch itself “off” briefly. If the trigger circuit has been restored the alarm will reset. If not, the attempt will fail and the alarm will reactivate. It will go on trying to reset itself every 15 to 20 minutes until the trigger circuits are restored; or the alarm is switched off.

The Exit delay, Entry delay and Bell Cut-off times may be changed by altering the values of R12, R8 & R11 respectively. The sensitivity of the Inertia Sensors is adjusted by R4. Set to minimum value, a light tap will activate the alarm. Set to maximum value, a heavy blow is required. If you are not using Inertia Sensors then replace R4 with a 220k fixed resistor. If you are not using normally open switches then leave out R1, C1 & Q1 and fit a link between the green Led and C2.

Construction:
The terminals are a good set of reference points. To fit them you’ll need to enlarge the holes to 1.3mm. Now turn the board over and cut the tracks in the 34 places shown. Make sure that the copper is cut all the way through. Sometimes a small strand of copper remains at the side of the cut and this will cause malfunction. If you don’t have the proper track-cutting tool, then a 6 to 8mm drill-bit will do. Just use the drill-bit as a hand tool; there is no need for a drilling machine.

Source :: http://www.zen22142.zen.co.uk/Circuits/Alarm/csza.htm

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By Tomaz Lazar – Ljubljana, Slovenia

A few months ago, I decided to build a compact, yet effective alarm. My demands were:- simple construction, reliable operation, very small power consumption, and, most of all, small size. I started with CMOS logic gates, but was soon forced to abandon the concept after a few unsuccessful (and far too complicated) attempts. Then I suddenly realized that a simple transistor switch might do the job and I was right.

As you can clearly see from the schematics, the circuit is utterly primitive and consists of two identical transistor switches. Each has its own alarm LED and they’re coupled to a neat 82dB buzzer. The two 1N4148 diodes are used to prevent a signal from one sensor from triggering both LEDs. The sensors used are either wire loops or normally closed reed switches or even a combination of both. You could, for example, tie a wire loop to your suitcase and place a reed switch to the door of your hotel room.

Since this little alarm is intended to be kept in arms reach at all times, there aren’t any provisions for automatic shutdown after a certain period of time. The buzzer will sound until you turn the whole circuit off or connect the wire loop back to the jumpers. The same goes for the two LEDs, each indicating its own zone.

Construction is not critical and there aren’t any traps for the novice. The two 100n capacitors aren’t really necessary, I just included them to make sure that there is no noise interference coming from the long wire loops. For transistors, you can use any NPN general-purpose audio amplifiers/switches (BC 107/108/109, BC 237/238, 2N2222, 2N3904…). Assemble the circuit on perf board. Together with the buzzer and a 9V battery, it should easily fit in a pocket-sized plastic box smaller than a pack of cigarettes. A fresh battery should suffice for weeks of continuous operation.

Source :: http://www.zen22142.zen.co.uk/Circuits/Alarm/alarm.html

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Two HiJack Alarms by 4001

The first circuit was designed for the situation where a hijacker forces the driver from the vehicle. If a door is opened while the ignition is switched on – the circuit will trip. After a few minutes delay – when the thief is at a safe distance – the alarm will sound and the engine will fail.

Notes:
You’re going to trip this alarm unintentionally. When you do – the LED will light and the Buzzer will give a short beep. The length of the beep is determined by C3. Its purpose is to alert you to the need to push the reset button. When you push the button – the LED will switch-off. Its purpose is to reassure you that the alarm has in fact reset.

If the reset button is not pressed then – about 3 minutes later – both the Siren and the Buzzer will sound continuously. The length of the delay is set by R7 & C4. For extra effect – fit a second siren inside the vehicle. With enough noise going on – you may feel that it’s unnecessary to fit the engine cut-out. In which case – you can leave out D8, D9, R11, R12, R13, C6, Q3, Q4 & Ry2.

Even if you missed the early warning provided by the Buzzer – there is still time to reset the alarm before Ry2 de-energizes – and the engine fails. This additional delay – currently about 1 minute – is set by C6 and R13.

To reset the circuit you must – EITHER turn off the ignition – OR close all of the doors – before you press the reset button. While BOTH the ignition is on – AND a door remains open – the circuit will NOT reset.

The reset button carries virtually no current – so any small normally-open switch will do. Eric Vandel from Canada suggests using a reed-switch hidden behind (say) the dash – and operated by a magnet. I think this is an excellent idea. As Eric said in his email: – “… that should keep any thief guessing for a while.”

The Flow Chart is another of Eric’s suggestions. It will help you to visualize how the alarm is operated. It also explains the sequence of events that lead to siren activation – and subsequent engine failure.
Circuit :Ron J
Email Ron:
Source:: http://www.zen22142.zen.co.uk/Circuits/Alarm/hijack.htm