On today’s podcast I will be discussing the need for a low tech means of protecting your store house, the smoke house, the chicken coop, etc.
It’s called a “BURGLAR ALARM”. Not high tech mind you, but very effective.
Now ADT and Brinks offer security services, but I’m offering you a covert means of protecting your stuff.
This is an alarm I found, and the associated image:
4 in 1 Burglar AlarmClick here for Circuit Diagram.
In this circuit, the alarm will be switched on under the following four different conditions: 1. When light falls on LDR1 (at the entry to the premises). 2. When light falling on LDR2 is obstructed. 3. When door switches are opened or a wire is broken. 4. When a handle is touched. The light dependent resistor LDR1 should be placed in darkness near the door lock or handle etc. If an intruder flashes his torch, its light will fall on LDR1, reducing the voltage drop across it and so also the voltage applied to trigger 1 (pin 6) of IC1. Thus transistor T2 will get forward biased and relay RL1 energise and operate the alarm. Sensitivity of LDR1 can be adjusted by varying preset VR1. LDR2 may be placed on one side of a corridor such that the beam of light from a light source always falls on it. When an intruder passes through the corridor, his shadow falls on LDR2. As a result voltage drop across LDR2 increases and pin 8 of IC1 goes low while output pin 9 of IC1 goes high. Transistor T2 gets switched on and the relay operates to set the alarm. The sensitivity of LDR2 can be adjusted by varying potentiometer VR2. A long but very thin wire may be connected between the points A and B or C and D across a window or a door. This long wire may even be used to lock or tie something. If anyone cuts or breaks this wire, the alarm will be switched on as pin 8 or 6 will go low. In place of the wire between points A and B or C and D door switches can be connected. These switches should be fixed on the door in such a way that when the door is closed the switch gets closed and when the door is open the switch remains open. If the switches or wire, are not used between these points, the points should be shorted. With the help of a wire, connect the touch point (P) with the handle of a door or some other suitable object made of conducting material. When one touches this handle or the other connected object, pin 6 of IC1 goes ‘low’. So the alarm and the relay gets switched on. Remember that the object connected to this touch point should be well insulated from ground. For good touch action, potentiometer VR3 should be properly adjusted. If potentiometer VR3 tapping is held more towards ground, the alarm will get switched on even without touching. In such a situation, the tapping should be raised. But the tapping point should not be raised too much as the touch action would then vanish. When you vary potentiometer VR1, re-adjust the sensitivity of the touch point with the help of potentiometer VR3 properly. If the alarm has a voltage rating of other than 6V (more than 6V), or if it draws a high current (more than 150 mA), connect it through the relay points as shown by the dotted lines. As a burglar alarm, battery backup is necessary for this circuit. Note: Electric sparking in the vicinity of this circuit may cause false triggering of the circuit. To avoid this adjust potentiometer VR3 properly. -
If you remove the switches, s2-s4, and the LDR2, you have an old fashioned INDUCTANCE ALARM. You know those touch lamps that get brighter each time you touch it? Same concept. By using 2 small 12v N batteries in a small black project case, with the relay applying power to a small piezeo alarm, you can make a small alarm system that would attach to the door knob of the store room, smoke house, or chicken coop. Because only the inductance wire would be ran from the box to the knob, it can be affixed the interior side of the doors, out of sight.
It would be missed by even an expert because it is so low tech. No InfraRed, or Motion Detectors to account for. Just a small thin wire.
Think about it. I believe you will see that this is an easy circuit to put together. A person with electronics background can whip this up in about an hour. A total newbie – maybe 2 hours.
Here is the parts list:
- R1 2.2K
- VR1 100K
- VR2 100K
- VR3 1M
- D1-4 1N4001
- C1 1000uf 25v
- C2 0.01uf
- C3 0.1uf
- IC1 556 counter
- IC2 7806 voltage regulator
- T1 BC158
- T2 SL100
- S1 – Momentary switch
- S2-S4 SPST switch
- RL1 6V 100 ohm SPDT relay
- LDR1-2 Photoresistors Radio Shack Catalog #: 276-1657