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Simple Mobile Detector Circuit
description source: http://www.electroschematics.com/1035/mobile-bug-detector-sniffer/
From a distance of 1.5 meters, this convenient mobile phone detector can identify the presence of an active mobile phone. Thus, it can be used to stop people from using their phones in private spaces like exam rooms. It is also helpful in identifying instances of illegal video transmission and eavesdropping on mobile phones.
Even when the mobile phone is maintained in silent mode, the circuit can still detect incoming and outgoing calls, SMS messages, and video transmissions. The mobile phone detector begins to beep and blink the LED as soon as it detects an RF transmission signal from an activated mobile phone. Until the signal transmission stops, the alarm keeps going off.
Step 1: Components
components list:-
| Resistors | Capacitors | Other | |
|---|---|---|---|
| 1.2M Ohm - 1 | 22 pf ceramic -3 | CA3130 - op-amp | |
| 2.2M Ohm -1 | 0.22uf ceramic -1 | PCB | |
| 1K Ohm -1 | 0.1 uf polyester/ceramic -1 | Red LED -1 | |
| 100K Ohm - 1 | 100uF/25V Electrolytic -1 | BC548 -1 | |
| 5Cm copper wire -1 |
Standard RF detectors don't offer enough sensitivity to detect signals in the GHz frequency range used in mobile phones. Wavelength 3.3 – 10 cm Transmission frequency: between.9 GHz and. Therefore, even a mobile insect requires an individual component able to pick up gigahertz transmissions.
In this circuit a 0.22μF disk capacitor (C3) is used to capture the RF signals from mobile phone(i.e. For the desired frequency, the distance between 2 leads is made to be 8 mm and lead length of capacitor is kept constant as which will be equal to 18 mm. The disk capacitor in combination with the leads forms a mini gigahertz loop antenna capable of capturing some RF signals radiated by at least one mobile phone.
The op-amp IC CA3130 (IC1) is utilized in the circuit as a current-to-voltage converter with capacitor C3 connected between its inverting and non-inverting input. It's a CMOS version with gate-protected p-channel MOSFET transistors in the input to provide very high impedance, unusually low skew current and differential speeds reaching several gigahertz. The CMOS output transistor can thus pull the output voltage to within 10 mV of either supply rail.
The lead inductance and the capacitor C3 provide a short-circuited transmission line that receives high-level signals from a mobile phone. This capacitor stores charge and discharges the same in a controlled manner, through input (IC1) data/write points. This will unbalance the input of IC1 and generates output voltage proportional to current.
Capacitor C4 together with high resistor value R1 ensures that the non-inverting input is maintained self-sufficient so that output can swing to a proper high logic position. Capacitor C4 is discharging via resistor R2. Signals InputIN and OutputOUT It is in high state if the output turns out to be low, this reflects back via feedback resistor R3; when the input signal = 6 V. Phase compensation and gain control for optimum frequency response is achieved through connection of a capacitor C5 (47pF) across the strobe(pinn 8), null inputs(pin1)of IC1.
When the cell phone detector signal is detected by C3, the output of IC1 becomes high and low alternately according to the frequency of the signal as indicated by LED1. This triggers monostable timer IC2 through capacitor C7. Capacitor C6 maintains the base bias of transistor T1 for fast switching action. The low-value timing components R6 and C9 produce very short time delay to avoid audio nuisance.
Assemble the cell phone detector circuit on a general purpose PCB as compact as possible and enclose in a small box like junk mobile case. As mentioned earlier, capacitor C3 should have a lead length of 18 mm with lead spacing of 8 mm. Carefully solder the capacitor in standing position with equal spacing of the leads. The response can be optimized by trimming the lead length of C3 for the desired frequency. You may use a short telescopic type antenna.
Use the miniature 12V battery of a remote control and a small buzzer to make the gadget pocket-size. The unit will give the warning indication if someone uses mobile phone within a radius of 1.5 meters.
