Introduction: Mobile Phone Detector Circuit

Printed Circuit Board

Step 1: INTRODUCTION TO Mobile Phone Detector Circuit

Mobile phone Detector is a device that can identify the existence of any active mobile phone in the vicinity and provides an indicator of the active cell phone in the vicinity. The Cell Phone Detector is essentially a Frequency Detector or a Current to Voltage Converter Device, which detects frequencies between 0.8 and 3.0 GHz (Mobile Band Frequencies). RL balanced circuit (Resistor–Inductor circuit) is not ideal for detection at the RF signals in GHz range.

This Mobile Detector Circuit will identify incoming / outgoing calls, tweets, video communication and any SMS or GPRS use within a 1 meter radius. This circuit is also useful for detecting mobile phones in restricted areas such as Exam halls, conference rooms, schools, etc. It's also useful when detecting illegal use or surveillance with secret Mobile Phone. It can identify the mobile phone RF transmission and triggers Buzzer to produce beep sound, even though the phone is stayed in Silent mode and this alert system continues to beep until RF signals are present.


  • Op-Amp CA3130 x 1
  • 2.2M resistor x 2
  • 100K resistor x 1
  • 1K resistor x 3
  • 100nF capacitor x 4
  • 22pF capacitor x 2
  • 100uF capacitor x 1
  • 9 V Power Supply
  • Battery Jack
  • LED
  • Transistor BC547 x 1
  • Transistor BC557 x 1
  • Buzzer
  • Antenna

Step 3: Op-Amp CA3130

The CA3130 can work in a Single supply voltage or in a dual supply mode. For now let’s concentrate on the +5V supply voltage circuit since this is the most used design for digital circuits. In this type, the VCC+ (pin 8) is connected to +5V supply voltage and the VCC (pin 4) is grounded to hold it at 0V potential.

CA3130 Specifications

  • Op-amp coupled with MOSFET at output

Wide power supply Range

  1. Singe supply – 5V to 16V
  2. Dual supply – ±2.5V to ±8V

  • Input Terminal current: 1mA
  • Maximum Output Voltage: 13.3V
  • Maximum source current: 22mA
  • Maximum sink current: 20mA
  • Supply current: 10mA
  • Common Mode Rejection Ration (CMRR): 80dB


  • Frequency Generator/Distorter
  • Mobile jammers
  • Voltage follower circuits
  • DAC circuits
  • Peak Signal/Noise detectors
  • Oscillator circuits


BC547 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. BC547 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 100mA, hence we cannot connect loads that consume more than 100mA using this transistor. To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA.

When this transistor is fully biased then it can allow a maximum of 100mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Base-Emitter (VBE) could be 200 and 900 mV respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 660 mV. BC547 as Switch

When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a Closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. As mentioned the biasing current should maximum of 5mA. Anything more than 5mA will kill the Transistor; hence a resistor is always added in series with base pin. The value of this resistor (RB) can be calculated using below formulae. RB = VBE / IB Where, the value of VBE should be 5V for BC547 and the Base current (IB depends on the Collector current (IC). The value of IB should not exceed mA. BC547 as Amplifier A Transistors acts as an Amplifier when operating in Active Region. It can amplify power, voltage and current at different configurations. Some of the configurations used in amplifier circuits are

Common emitter amplifierCommon collector amplifierCommon base amplifierOf the above types common emitter type is the popular and mostly used configuration. When uses as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulae DC Current Gain = Collector Current (IC) / Base Current (IB)

Step 5: Resistors

  • 2.2M resistor x 2
  • 100K resistor x 1
  • 1K resistor x 3

Step 6: Capacitors

  • 100nF capacitor x 4
  • 22pF capacitor x 2
  • 100uF capacitor x 1

Step 7: Barrel Jack

Step 8: 9V DC Power Supply


Features / Technical Specifications:

  • Package Type: TO-92
  • Transistor Type: PNP
  • Max Collector Current(IC): -100mA
  • Max Collector-Emitter Voltage (VCE): -45V
  • Max Collector-Base Voltage (VCB): -50V
  • Max Emitter-Base Voltage (VBE): -5V
  • Max Collector Dissipation (Pc): 500 Milliwatt
  • Max Transition Frequency (fT): 100 MHz
  • Minimum & Maximum DC Current Gain (hFE): 125 to 800
  • Max Storage & Operating temperature Should be: -65 to +150Centigrade

Step 10: Schematic

Step 11: PCB Layout

Step 12: 3D Viewer of PCB

Step 13: Ordering the PCBs From JLCPCB

Full Process is shown using Screenshots Step-wise.

Now we have got the PCB design and it’s time to order the PCB’s. For that, you just have to go to, and click on “QUOTE NOW” button.

JLCPCB are also sponsor of this project. JLCPCB (ShenzhenJLC Electronics Co., Ltd.), is the largest PCB prototype enterprise in Chinaand a high-tech manufacturer specializing in quick PCB prototype and small-batch PCB production. You can order a minimum of 5 PCBs for just $2.

To get the PCB manufactured, upload the gerber file you downloaded in the last step. Upload file or you can also drag and drop the gerber files.

After uploading the zip file, you’ll see a success message at the bottom if the file is successfully uploaded.

You can review the PCB in the Gerber viewer to make sure everything is good. You can view both top and bottom of the PCB. After making sure our PCB looks good, we can now place the order at a reasonable price. You can order 5 PCBs for just $2 but if it’s your first order then you can get 5 PCBs for $2.

To place the order, click on “SAVE TO CART” button. My PCBs took 2 days to get manufactured and arrived within a week using DHL delivery option. PCBs were well packed and the quality was really good.