Introduction: Simple Mobile Detector Circuit

Picture of Simple Mobile Detector Circuit

simple mobile detector circuit using  CA3130 op-amp

description source:

This handy mobile  phone detector  can sense the presence of an activated mobile cellphone from a distance of one and-a-half metre. So it can be used to prevent use of mobile phones in examination halls, confidential rooms, etc. It is also useful for detecting the use of mobile phone for spying and unauthorized video transmission.

The circuit can detect both the incoming and outgoing calls, SMS and video transmission even if the mobile phone is kept in the silent mode. The moment the mobile  phone detector detects RF transmission signal from an activated mobile phone, it starts sounding a beep alarm and the LED blinks. The alarm continues until the signal transmission ceases.

Step 1: Components

Picture of Components

components list

1, CA3130  - op-amp 
2, PCB
3, Resistors all 1/4W ,
    1.2M Ohm - 1
     2.2M Ohm -1
     1K Ohm -1
     100K Ohm - 1
4, Capacitors
     22 pf ceramic -3
     0.22uf ceramic -1
     0.1 uf  polyester/ceramic -1
    100uF/25V  Electrolytic  -1
5, Red LED -1
6, BC548 -1
7, 5Cm copper wire -1


Step 2: Circuit Diagram

Picture of Circuit Diagram

An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in the GHz frequency band used in mobile phones. The transmission frequency of mobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So a circuit detecting gigahertz signals is required for a mobile bug.

Here the circuit uses a 0.22μF disk capacitor (C3) to capture the RF signals from the mobile phone. The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mm between the leads to get the desired frequency. The disk capacitor along with the leads acts 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 with capacitor C3 connected between its inverting and non-inverting inputs. It is a CMOS version using gate-protected p-channel MOSFET transistors in the input to provide very high input impedance, very low input current and very high speed of performance. The output CMOS transistor is capable of swinging the output voltage to within 10 mV of either supply voltage terminal.

Capacitor C3 in conjunction with the lead inductance acts as a transmission line that intercepts the signals from the mobile phone. This capacitor creates a field, stores energy and transfers the stored energy in the form of minute current to the inputs of IC1. This will 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 stable for easy swing of the output to high state. Resistor R2 provides the discharge path for capacitor C4. Feedback resistor R3 makes the inverting input high when the output becomes high. Capacitor C5 (47pF) is connected across ‘strobe’ (pin 8) and ‘null’ inputs (pin 1) of IC1 for phase compensation and gain control to optimize the frequency response.

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.

Step 3: Assembling

Picture of Assembling

Step 4: Final Prototype

Picture of Final Prototype

Step 5: PCB Layout Pdf File [actual Size]

Step 6: Working Video


SierraW9 made it! (author)2017-09-13

I tried to build your circuit for my science fair project. I started this in June. The science fair is tomorrow. I was a complete novice at electronics before I began this project (that was one of the reason why I did the project, to learn), so I did not know that your circuit diagram is incomplete and that I would need to build a complete different circuit to actually get it two work. You reference the complete circuit when you explain how it works, yet you don't show the whole circuit diagram??? You didn't even write the background information, but just copy and pasted. At least say where you got it from! If you are going to build this circuit, DO NOT FOLLOW THIS INSTRUCTABLE!!!!! Instead go to this website, It has the complete circuit diagram. The chances of you getting this circuit to work ARE VERY LOW and even if it does work, it won't work very well. I have included photos of our failed PCB to show that I spent 4 months working on a project that was going to fail from the start.

ovij (author)2017-09-09

where will i find the board?

GiapN1 (author)2017-04-09

Sir Jestin, Op amp CA3130 is not available in my country. Is there any other op amp I could use as a similar one ? Thanks in advance !

Deepeshguru (author)2016-05-24

Can we operate it at 9 v

mohitsaiteja (author)Deepeshguru2017-03-09

ya we can operate at

9v also

Subham007 (author)2017-03-02

Does it work??? What is the length of antenna??? Is it work on smartphone??

Gokul678 (author)2016-11-24

the light still on when connected

gabat (author)2014-09-29

I would like to ask where is that brown wire connected to.

gabat (author)gabat2014-09-29

where is that wire connected to

Jestin_Cubetech (author)gabat2014-10-18

it's not an antenna ,output from mobile detector circuit.

Is it going to detect on basic cell activation or smartphones aswell.


how much the length of anthena

Jestin_Cubetech (author)gabat2014-10-07

NC pin (no connection)

patelkeyur4653 (author)gabat2014-10-17

It's antenna....

rahulnaik388 (author)2016-09-12

Thanks you

PriankT (author)2016-06-04

Please help I have made a cell phone detector but the buzzer or led just keeps glowing

PriankT (author)2016-06-04

Please help I have made a cell phone detector but the buzzer or led just keeps glowing

AlanD30 (author)2016-05-29

Hi, Will this detect phone signal basestations and towers (in the absence of a phone) too?

savan28 made it! (author)2015-09-27

Yes it worked :-D

Momykhan (author)savan282016-02-14

Hye,,, Plx Help me, my project is not working. Reply me I am waiting

savan28 (author)Momykhan2016-02-15

Hi Momykhan,
Firstly check if you have correctly made the circuit and all the components are working, also try using a newer IC and the swap the other electrical components, If it still does not work then, I Guess the problem might be with the Cell Phone that you may have used, The circuit basically detects only 2G spectrum and not 3G or 4G. Try using a 2G phone and if still doesn’t work then try using a different service provider.
Alternating try using this circuit, , this circuit can detect 3G spectrum as well.
Hope this helps you.

Momykhan (author)savan282016-04-24

Thanks aloottt,,,

PravinA4 (author)2016-03-10

I have mounted all components of mobile detector on bread board and am fail to detect the mobile. As per your advice i have used 2G mobile. Will you please say me which antenna should i use in circuit. And where am i wrong in please please

Levin john (author)2016-02-19

Nice work

namindu (author)2015-12-09

Can I use LM386 IC

DARPANA (author)2015-11-18

It did work but not well as the circuit displayed here is half and incomplete.

Here is the link to the full circuit which has 555 Timer IC and buzzer as well along with some other components. Only then it worked with full compliance.

Good luck and I thinik that one should not mislead people.

Just look at the circuit and then read the description of the project in this instructable, you will come to know why I am saying this.

Here is the link:

Check it out yourself.

zulhafiszan (author)2015-09-04

hello... how to make led light become more bright

dharanir (author)2015-09-02

Hi jestin i need pdf fomat of this project plz

Mohd DzulhusneeB (author)2015-04-22

hello can i ask how much the length of anthena should be use help me

zulhafiszan (author)2015-09-02

how much the length of anthena should be use in this project

admin please help me i need your help

zulhafiszan (author)2015-09-02

what the type simulation i can use for this project

zulhafiszan (author)2015-09-02


MariC5 (author)2015-08-24


LavanyaR2 (author)2015-08-21

yaswanth raj (author)2015-05-31

Insted of using 12v shall v use 9v

TanveerA1 (author)2015-04-06

can i please get the breadboard equivalent for the given connection

TanveerA1 (author)2015-04-06

can i please get the bread board equivalent for the given connecton

sarathikkl (author)2015-01-23

hello friend, how long (distance) the circuit will detected the signal between the circuit and mobile phone

sandeepkr.chandolia (author)2014-11-25

ye project kam bhi krta h ky...

y2kare_007 (author)2014-11-02

Does this detect signals from smartphone.. 4g LTE? Also when I connected a battery the led stays on constantly.. Any solution?

y2kare_007 (author)2014-09-30

will this circuit be able to detect 4G signals ?

patelkeyur4653 (author)2014-10-18

It's not working man
after lots of troubleshooting
really disappointed me....

bhai ye project bna liya ky kam krta h ya nhi

MuthuL (author)2014-10-20

It detects only the signals from basic models.why it is not detecting the signals from smartphones???

Emran_khan (author)2014-10-20

This circuit detects simple mobile phones but not the smartphone. Furthermore this circuit detects the transmission and reception frequency of mobile phones that ranges from 0.9 to 3 GHz. Then what is the Tx/Rx frequency of smartphones?

patelkeyur4653 (author)2014-10-17

How can i increase frequency range?

y2kare_007 (author)2014-09-30

Also if i want to make this circuit compact, can i use SMD components ? will the frequency range and sensitivity be affected if i do so ?

sandeepkr.chandolia (author)2014-09-27

connecting buzzer and R4 parallel?????? or replace R4 by buzzer..

plz reply fast

About This Instructable




Bio: embedded system enthusiast ...
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