To begin with, in this Mobile Phone Detector Circuit using Op-Amp we will show how to make one circuit to detect mobile phones nearby.
The circuit detects radio signals from an active mobile phone, helping to identify unauthorized phone usage in quiet places like meeting rooms and libraries.
However, always check local rules and regulations before using this circuit in restricted areas that prohibit mobile phones.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 100k | 1 |
| 220k | 1 | |
| 1k | 1 | |
| Preset 2.2M | 1 | |
| Capacitors | Electrolytic 1μF 16V | 2 |
| Electrolytic 100μF 16V | 1 | |
| Semiconductors | Op amp IC LM358 | 1 |
| Transistor BC547 | 1 | |
| LED 20mA 5mm | 1 | |
| ON/OFF Switch | 1 | |
| Antenna | 1 | |
| Battery 1.5V | 3 |
Even if mobile phone is in silent mode this device can find call coming or going, message, SMS, internet and video using.
LED on device start blinking when it catches radio signal (RF) from working mobile phone which keeps blinking till signal stops.
Circuit and how it work is showing in circuit diagram.
Here, the circuit uses an op-amp LM358 as a mobile phone detector and its main components are the LM358 IC1 and an NPN transistor BC547 T1.
When mobile phone is ON it send radio wave (RF signal) all around and capacitor C1 take this signal from phone and C1 is very important in this circuit.
Hence, LED1 blink when C1 take RF signal and send to IC1 input.
One preset VR1 2.2M is to change how far the circuit can catch signal and transistor T1 make signal stronger from IC1 pin 1.
Also, this circuit work with GPRS, 2G and both auto/manual network type, but maybe it does not catch 3G, WCDMA or HSDPA signal.
Formula:
Engineers mainly use op-amp circuits to detect electromagnetic signals from mobile phones.
The exact formula depends on the circuit design, including the comparator threshold level, the components used for rectification and filtering and the cutoff frequency of the band-pass filter.
Resistor and capacitor values in bandpass and low pass filter can be find using normal RC circuit formula.
Example for low pass filter and cut-off frequency (fc) is:
fc = 1 / 2πRC
where:
- R is resistor
- C is capacitor.
Also, center frequency and bandwidth can be find same way for filters.
Note:
It also depend on center frequency and bandwidth of bandpass filter to choose which frequency to detect; check if antenna can catch that frequency range or not.
When picking op-amp think about what we need like power voltage, bandwidth and other things.
Detector sensitivity can change by adjusting reference voltage or gain in op-amp circuit; this is just simple start point.
Hence, if we need different result maybe we must change component values, circuit design, sensitivity, range and so on.
How to Build:
To build a Mobile Phone Detector Circuit using Op-Amp following are the connection steps to keep in mind:
- First, connect pin 4 of LM358 IC1 to ground.
- Next, connect pin 8 of IC1 to power supply of positive side.
- Then solder pin 3 of IC1 to the place where R1 and R2 meet
- Connect other side of R1 to IC1 pin 2 and other side of R2 connect to place where C1 and VR1 join.
- Also, one side of VR1 goes to point where R2 and C1 join and other side of VR1 goes to ground.
- After that, one side of C1 connect to R2 and VR1 point and other side of C1 connect to pin 1 of IC1.
- Make sure the LED cathode, which is the short leg, connects to ground.
- Now, connect transistor T1 collector to power supply of positive using resistor R3.
- Emitter of T1 goes to ground and base of T1 connect to IC1 pin 1.
Power Supply:
- First, connect power supply positive to Vcc and connect power supply negative to GND.
Antenna:
- Also, use small piece of wire as antenna which will help to catch better signal.
- Turn ON the circuit and place a mobile phone near it and if the LED blinks, the circuit detects the RF signal from the mobile phone.
Modifications:
- Use VR1 to adjust frequency for correct sensitivity.
Take Note:
- Making circuit is not easy as every part must be correct and if anyone do not know electronics then better to ask someone who knows.
- Also, check with local laws where some countries do not allow this kind of device.
Conclusion:
To conclude, always remember using this Mobile Phone Detector Circuit using Op-Amp we must be careful; also follow safety and legal rules when building and using it.