In this Mobile Phone Detector Circuit using Op-Amp we will show how to make one circuit to detect mobile phones nearby.
It can catch the radio signal from phone when phone is ON and it tells if someone using phone in quiet place like meeting room or library where phone are not allowed.
But be careful maybe we cannot use this circuit in place where mobile phone are not allowed at all.
Always check the rules before using it.
Circuit Working:
Parts List:
| Category | Item | 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.
Mobile phone detector is made using op-amp LM358.
Main parts are LM358 IC1 and one NPN transistor BC547 T1.
When mobile phone is ON it send radio wave (RF signal) all around.
Capacitor C1 take this signal from phone and C1 is very important in this circuit.
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.
Transistor T1 make signal stronger from IC1 pin 1.
This circuit work with GPRS, 2G and both auto/manual network type.
But maybe it does not catch 3G, WCDMA or HSDPA signal.
Formula:
Circuit using op-amp is mostly made to find electromagnetic signal from mobile phone.
Exact formula depend on how circuit is build like what level the comparator is used and what parts do rectifying and filtering and what bandpass filter cut-off is.
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.
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:
- Connect pin 4 of LM358 IC1 to ground.
- Connect pin 8 of IC1 to power supply of positive side.
- Solder pin 3 of IC1 to the place where R1 and R2 meet.
- Connect other side of R1 to IC1 pin 2.
- Other side of R2 connect to place where C1 and VR1 join.
- One side of VR1 goes to point where R2 and C1 join.
- Other side of VR1 goes to ground.
- One side of C1 connect to R2 and VR1 point.
- Other side of C1 connect to pin 1 of IC1.
- Be sure LED cathode the short leg is connected to ground.
- Connect transistor T1 collector to power supply of positive using resistor R3.
- Emitter of T1 goes to ground.
- Base of T1 connect to IC1 pin 1.
Power Supply:
- Connect power supply positive to Vcc.
- Connect power supply negative to GND.
Antenna:
- Use small piece of wire as antenna which will help to catch better signal.
- Turn ON the circuit.
- Turn ON mobile phone near the circuit.
- If LED is blinking it means mobile phone RF signal is detected.
Modifications:
- Use VR1 to adjust frequency for correct sensitivity.
Take Note:
- Making circuit is not easy as every part must be correct.
- 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:
Always remember using this Mobile Phone Detector Circuit using Op-Amp we must be careful.
Follow safety and legal rules when building and using it.
References:
Implementation of Cell Phone Detection Mobile Robot for Restricted Areas Using NodeMCU