04-02-2016, 02:24 PM
INTRODUCTION
The most common electronic equipment used is cell phones. With advancement in communication technology, the requirement of cell phones has increased manifold.
A cell phone typically transmits and receives signals in the frequency range of 0.9 to 3GHz. This seminar provides a simple circuit to detect the presence of an activated cell phone by detecting these signals.
Detector ckt
The detector circuit consists of an inductor, diode, a capacitor and a resistor. Here an inductor value of 10uH is chosen. A Schottky diode BAT54 is chosen as the detector diode, which can rectify low AC signal. The filter capacitor chosen in a 100nF ceramic capacitor, used to filter out AC ripples. A load resistor of 100 Ohms is used.Then the signal is filter in the range of 0.9-3GHZ by the help of RC filter ckt.
AMPLIFIER CKT.
Here a simple BJT BC547 is used in common emitter mode. Since the output signal is of low value, the emitter resistor is not required in this case. The collector resistor value is determined by the value of battery voltage, collector emitter voltage and collector current. Now the battery voltage is chosen to be 12 V operating point collector emitter voltage is 5 V and collector current is 2 mA. This gives a collector resistor of approx 3 K. Thus a 3 K resistor is used as Rc. The input resistor is used to provide bias to the transistor and should be of larger value, so as to prevent the flow of maximum current. Here we chose a resistor value of 100 K.
The most common electronic equipment used is cell phones. With advancement in communication technology, the requirement of cell phones has increased manifold.
A cell phone typically transmits and receives signals in the frequency range of 0.9 to 3GHz. This seminar provides a simple circuit to detect the presence of an activated cell phone by detecting these signals.
Detector ckt
The detector circuit consists of an inductor, diode, a capacitor and a resistor. Here an inductor value of 10uH is chosen. A Schottky diode BAT54 is chosen as the detector diode, which can rectify low AC signal. The filter capacitor chosen in a 100nF ceramic capacitor, used to filter out AC ripples. A load resistor of 100 Ohms is used.Then the signal is filter in the range of 0.9-3GHZ by the help of RC filter ckt.
AMPLIFIER CKT.
Here a simple BJT BC547 is used in common emitter mode. Since the output signal is of low value, the emitter resistor is not required in this case. The collector resistor value is determined by the value of battery voltage, collector emitter voltage and collector current. Now the battery voltage is chosen to be 12 V operating point collector emitter voltage is 5 V and collector current is 2 mA. This gives a collector resistor of approx 3 K. Thus a 3 K resistor is used as Rc. The input resistor is used to provide bias to the transistor and should be of larger value, so as to prevent the flow of maximum current. Here we chose a resistor value of 100 K.