Abstract
The circuit can detect both the incoming and outgoing calls, SMS and video transmissioneven if the mobile phone is kept in the silent mode. The moment the bug Detect RFtransmission signal from an activated mobile phone, it starts sounding a beep alarm andthe LED blink. The alarm Continues until the signal transmission Cease.
ExplanationAn ordinary RF detector using tuned LC circuits is not suitable for detecting signalsin the GHz frequency band used in mobile phones. The transmission frequency ofmobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So a circuitdetecting gigahertz signals is required for a mobile bug.
Here the circuit uses a 0.22μF disk capacitor (C3) to capture the RF signals from themobile phone. The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mmbetween the leads to get the desired frequency. The disk capacitor along with the leadsacts as a small gigahertz loop antenna to collect the RF signals from the mobile phone.
Op-amp IC CA3130 (IC1) is used in the circuit as a current-to-voltage converter withcapacitor C3 connected between its inverting and non-inverting inputs. It is a CMOSversion using gate-protected p-channel MOSFET transistors in the input that Provide veryhigh input impedance, very low input current and very high speed of performance. Theoutput CMOS transistor is Capable of swinging the output voltage to within 10 mV ofeither supply voltage terminal.
Capacitor C3 in conjunction with the lead inductance acts as a transmission line Thatintercepts the signals from the mobile phone. This capacitor creates a field, stores energyand transfers the Stored energy in the form of minute current to the inputs of IC1. Thiswill upset the balanced input of IC1 and convert the current into the Corresponding output voltage.
Capacitor C4 along with high-value resistor R1 keeps the non-inverting input stablefor easy swing of the output to high state. Resistor R2 provides the discharge path forcapacitor C4. Feedback resistor R3 makes the inverting input high when the outputBecomes high. Capacitor C5 (47pF) is connected across 'strobe' (pin 8) and 'null'inputs (pin 1) of IC1 for phase compensation and gain control to Optimise the frequencyresponse.
When the cell phone detector signal is detected by C3, the output of IC1 high Dominateand low alternately according to one the frequency of the signal as indicated by LED1. Thistimer triggers monostable IC2 through capacitor C7. Capacitor C6 maintaine the basebias of transistor T1 for fast switching action. The low-value timing components R6 andC9 produce very short time delay to avoid audio nuisance.
Assemble the cell phone detector circuit on a general purpose PCB as compact aspossible and enclose in a small box like junk mobile case. As mentioned earlier, capacitorC3 Should have a lead length of 18 mm with lead spacing of 8 mm. Carefully solderthe capacitor in standing position with equal spacing of the leads. The response can nooptimized by trimming the lead length of C3 for the desired frequency. You may use ashort telescopic type antenna.Use the miniature 12V battery of a remote control and a small buzzer to make the gadgetpocket-size. The unit will give the warning indication if someone uses mobile phonewithin a radius of 1.5 meters.
The circuit can detect both the incoming and outgoing calls, SMS and video transmissioneven if the mobile phone is kept in the silent mode. The moment the bug Detect RFtransmission signal from an activated mobile phone, it starts sounding a beep alarm andthe LED blink. The alarm Continues until the signal transmission Cease.ExplanationAn ordinary RF detector using tuned LC circuits is not suitable for detecting signalsin the GHz frequency band used in mobile phones. The transmission frequency ofmobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So a circuitdetecting gigahertz signals is required for a mobile bug.
Here the circuit uses a 0.22μF disk capacitor (C3) to capture the RF signals from themobile phone. The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mmbetween the leads to get the desired frequency. The disk capacitor along with the leadsacts as a small gigahertz loop antenna to collect the RF signals from the mobile phone.
Op-amp IC CA3130 (IC1) is used in the circuit as a current-to-voltage converter withcapacitor C3 connected between its inverting and non-inverting inputs. It is a CMOSversion using gate-protected p-channel MOSFET transistors in the input that Provide veryhigh input impedance, very low input current and very high speed of performance. Theoutput CMOS transistor is Capable of swinging the output voltage to within 10 mV ofeither supply voltage terminal.
Capacitor C3 in conjunction with the lead inductance acts as a transmission line Thatintercepts the signals from the mobile phone. This capacitor creates a field, stores energyand transfers the Stored energy in the form of minute current to the inputs of IC1. Thiswill upset the balanced input of IC1 and convert the current into the Corresponding output voltage.
Capacitor C4 along with high-value resistor R1 keeps the non-inverting input stablefor easy swing of the output to high state. Resistor R2 provides the discharge path forcapacitor C4. Feedback resistor R3 makes the inverting input high when the outputBecomes high. Capacitor C5 (47pF) is connected across 'strobe' (pin 8) and 'null'inputs (pin 1) of IC1 for phase compensation and gain control to Optimise the frequencyresponse.
When the cell phone detector signal is detected by C3, the output of IC1 high Dominateand low alternately according to one the frequency of the signal as indicated by LED1. Thistimer triggers monostable IC2 through capacitor C7. Capacitor C6 maintaine the basebias of transistor T1 for fast switching action. The low-value timing components R6 andC9 produce very short time delay to avoid audio nuisance.
Assemble the cell phone detector circuit on a general purpose PCB as compact aspossible and enclose in a small box like junk mobile case. As mentioned earlier, capacitorC3 Should have a lead length of 18 mm with lead spacing of 8 mm. Carefully solderthe capacitor in standing position with equal spacing of the leads. The response can nooptimized by trimming the lead length of C3 for the desired frequency. You may use ashort telescopic type antenna.Use the miniature 12V battery of a remote control and a small buzzer to make the gadgetpocket-size. The unit will give the warning indication if someone uses mobile phonewithin a radius of 1.5 meters.
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The new invention on cell phone detector has arrived in the market for the legal phones.This is the best techniques for the new generation.This is a best projects for students to know the great idea with this technique.
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