Here the notebook anti theft protector circuit to secure your important netbook / notebook from stealing. Basically, this is a mini security alarm generator. Fixed inside the notebook case, it will definitely sound a noisy alarm when a person attempts to grab the notebook. This very sensitive circuit utilizes a homemade tilt switch to turn on the alarm system through tilting of the laptop computer case.
The circuit utilizes readily available parts and also can easily be constructed on a little piece of general-purpose PCB or a Vero board. This circuit is operated by a 12V miniature battery applied in remote control devices.
IC TLO71 (IC1) is utilized as a voltage comparator with a potential divider composed of R2 and R3 delivering fifty percent power supply voltage at the non-inverting input (pin 3) of IC1. The inverting input gets a higher voltage through a water-activated tilt switch only when the probes in the tilt switch make contact with water. When the tilt switch is maintained in the horizontal position, the inverting input of IC1 receives a higher voltage than its noninverting input and the output continues to be low.
The CD4538 (IC2) is utilized as a monostable multivibrator with timing factors R5 and C1. Considering the shown values, the output of IC2 continues to be low for a duration of three minutes. CD4538 is an accuracy monostable multivibrator free from incorrect triggering and also is much more reliable compared to the well-known timer IC 555. Its output comes to be high when power is turned on and it gets low when the trigger input (pin 5) receives a low to high transition pulse.
The circuit device is fixed inside the notebook case in horizontal position. In this position, water inside the tilt switch properly shorts the contacts, so the output of IC1 continues to be low. The alarm system generator stays silent in the standby mode as trigger pin 5 of IC2 is low. When a person attempts to grab the notebook case, the unit takes the vertical position and the tilt switch breaks the electrical contact between the probes. Instantly the output of IC1 comes to be high and monostable IC2 is triggered. The low output from IC2 triggers the PNP transistor (T1) and then the buzzer starts beeping.
Construct the circuit as compactly as feasible so as to make the unit matchbox dimension. Make the tilt switch working with a small (2.5 centimeters long and 1cm wide) plastic bottle with two stainless pins as contacts. Fill two-third of the bottle with water such that the contacts never make electrical path when the tilt switch is in vertical position. Make sure the bottle is leakproof with adhesive or wax.
Fix the tilt switch inside the enclosure of the circuit in horizontal position. Fit the unit inside the notebook case in horizontal position working with adhesive. Work with a miniature buzzer and a micro switch (S1) for making the device small and lightweight. Maintain the notebook case in horizontal position and turn on the circuit. Your notebook is right now secured.