Swith For diagram

This FREQUENCY MODULATION radio controlled anti-theft warning signal can be utilised with any vehicle having 6 – to 12-volt DIRECT ELECTRIC CURRENT power grid. The miniskirt VIRAL HAEMORRHAGIC FEVER, FREQUENCY MODULATION sender is climbed on the vehicle at dark, when it is parked in the railcar porch or parking. 

The recipient CXA1019, an IC-based FREQUENCY MODULATION wireless mental faculty, which is freely uncommitted on the marketplace at a sensible damage, stays inside. The recipient is tuned up to the relative frequency of the sender. When the vector is on and the signs are experienced by FREQUENCY MODULATION receiving set, no sibilation sound is uncommitted at the recipient turnout. Thus transistor T2 (BC548) not to follow up.

This small circuit, based on popular CMOS NAND chip CD4093, can be effectively used for protecting your expensive car audio system against theft. When 12V DC from the car battery is applied to the gadget (as indicated by LED1) through switch S1, the circuit goes into standby mode. LED inside optocoupler IC1 is lit as its cathode terminal is grounded via the car audio (amplifier) body. As a result, the output at pin 3 of gate N1 goes low and disables the rest of the circuit.

Whenever an attempt is made to remove the car audio from its mounting by cutting its connecting wires, the optocoupler immediately turns off, as its LED cathode terminal is hanging. As a result, the oscillator circuit built around gates N2 and N3 is enabled and it controls the ‘on’/‘off’ timings of the relay via transistor T2. (Relay contacts can be used to energise an emergency beeper, indicator, car horns, etc, as desired.)

Different values of capacitor C2 give different ‘on’/‘off’ timings for relay RL1 to be ‘on’/‘off’. With 100µF we get approximately 5 seconds as ‘on’ and 5 seconds as ‘off’ time. Gate N4, with its associated components, forms a self-testing circuit. Normally, both of its inputs are in ‘high’ state. However, when one switches off the ignition key, the supply to the car audio is also disconnected.

Thus the output of gate N4 jumps to a ‘high’ state and it provides a differentiated short pulse to forward bias transistor T1 for a short duration. (The combination of capacitor C1 and resistor R5 acts as the differentiating circuit.)As a result, buzzer in the collector terminal of T1 beeps for a short duration to announce that to announce that the security circuit is intact. This ‘on’ period of buzzer can be varied by changing the values of capacitor C1 and/or resistor R5. After construction, fix the LED and buzzer in dashboard as per your requirement and hide switch S1 in a suitable location. Then connect lead A to the body of car stereo (not to the body of vehicle) and lead B to its positive lead terminal. Take power supply for the circuit from the car battery directly.

Author:T.K  Hareendran Copyright: Circuit Ideas