Cellphone Calling Detector

1.    INTRODUCTION

Mobile-phones emits small amount of electromagnetic signal via the radio waves which is RF energy. Every Mobile-phone has a low power transmitter in them. While talking over the cell-phone, the transmitter takes the sound of voice & changes it into a continuous sine wave. Sine wave is measured in terms of frequency.Transmitter sends the sine wave to antenna. Antenna transmits the sine wave in the form of electromagnetic signal to the BTS. Cell-phone works by communication between service n/w through BTS or cell tower. Cell towers divide the city into small areas or cells. As the user moves from one cell to another, the signal along with the information is handed over from tower to tower.

 Electromagnetic radiation (EMR) is at the heart of modern mobile phone data communications networks. The way a mobile phone and local base stations  communicate between each other is by using EMR in the radio wave part of the spectrum  On switch-on your mobile sends digital information pulses by rapidly switching on and off the radio waves rather like a fast Morse code signal. Your text or voice is also converted into a series of digital pulses and sent across the network to be decoded (reassembled) by another mobile phone you dialled.

It is commonly seen that we people forget where we placed our cellphones.this habit will be a cause for losing it,when the phone is in silent mode.some of us thought of solving the problem with the help of an electronic circuit and we are able to set up a circuit that enables us to locate the phone even if its in silent mode.

Described is a simple low cost home-made device that converts the radio wave energy from a mobile phone signal into electricity to light an LED

2.    BLOCK DIAGRAM

3.    BLOCK DIAGRAM DESCRIPTION

FIRST PART OF THE CIRCUIT IS A RECEIVER.

            PREAMPLIFIER (preamp) is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio (SNR). The noise performance of a preamplifier is critical; according to Friss' formula, when the gain of the preamplifier is high, the SNR of the final signal is determined by the SNR of the input signal and the noise figure of THE PREAMPLIFIER In general, the function of a preamplifier is to amplify a low-level signal to line-level.

4.    CIRCUIT DIAGRAM

5.    CIRCUIT DESCRIPTION

The receiver coil L1 detects the signal and the detected signal is amplified by transistor Q1 and drives the monostable input pin of IC1. The IC's output voltage is doubled by C2 & D2 in order to drive the LED1 at a suitable peak-voltage. Stand-by current drawing is less than 200μA.Sensitivity of this circuit depends on the sensor coil type. L1 can be made by winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former. Remove the coil from the former and wind it with insulating tape, thus obtaining a stand-alone coil. Transistor Q1 is responsible for flipping the trigger pin on the 555 timer (pin 2). The transistor does the flipping when the pickup circuit comprising of L1 and C1 receives a signal from the cell phone.

 So, the objective would be to make this part of the circuit more sensitive to the signals. I can think of 3 potential ways to do this...

1.      You can play around with coil L1 to see if you can create a more sensitive pick-up. Try rotating the plane of the coil (vertical/horizontal) when it rests on the table. If that doesn't work, you can try playing about with the number of turns. Try putting on a few more turns... if that makes it more sensitive, then keep on going until you find that it's at the maximum sensitivity. If adding more turns made it less sensitive, then try removing turns until you find maximum sensitivity.

1.      The biasing of Q1 is provided by R1. Just the biasing current/voltage alone is not enough to trigger the 555 timer, however when the received signal from the phone is coupled into the circuit, the two combined are enough to trigger it. So, one option might be to have the bias current in Q1 working closer to the trigger point, meaning that an even weaker signal should still do the triggering. Try replacing R1 with an 82k resistor in SERIES with a 22k variable resistor. Initially, set the variable resistor to it's maximum value. Then, make a call to your cell phone that's placed a meter or so away, and slowly decrease the value of the variable resistor until the LED (hopefully) illuminates. You need to make sure that it's only being triggered while the phone is ringing. If the LED illuminates even when the phone is not ringing, then the biasing current has gone too high, and the trigger point has been passed. If this happens, then you may need to go to step 3...

2.      If neither of the above worked for you, then you'll probably need to either a) replace Q1 with something that has a higher ac Beta value, but of the same or very similar dc Beta value; or b) modify the circuit to include some kind of "pre amplifier" for the signal that's picked up by the L1 C1 circuit.

6.    WORKING

            When a radio wave passes across a metal object the EM fields cause the charged electrons in the metal to oscillate and this causes small AC currents at the same frequency to be induced into the metal If a mobile is brought near to the CIRCUIT and a call or text is made [5] the radio waves emitted from the phone pass across the CIRCUIT This induces a voltage into the antenna (thE COIL) and if it is close enough will be large enough to light the LED. When a call is coming to the mobile phone, the transmitter inside it becomes activated.

            The frequency of the transmitter is around 900MHz.The coil L1 picks up these oscillations by induction and feds it to the base of Q1.This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at its output pin (pin 3) to blink.The blinking of the LED is the indication of incoming call. The electric and magnetic fields making up the EM wave are orthogonal (they are at right angles to each other as they pass through space) to each other but depending how they are generated by the transmitting antenna can arrange themselves in any orientation with respect to the ground. If the electric field is parallel with the ground we say the wave is 'horizontally polarised' while if its normal to the ground we say its 'vertically polarised'.

            The loop antenna will respond best to one type of polarisation (depending on its orientation) so it's worth experimenting with the orientation of the mobile (or the loop) to get the strongest signal - brightest LED. 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.

            On a new LED the long lead is the positive (anode) while the short lead is the negative (cathode). The germanium diode has a line (band) around the end which is the cathode. When correctly wired the LED and the germanium diodes are connected so they both allow current to pass in the same direction, i.e. in the circuit diagram the arrows point in the same direction. In practice this means the LED and germanium diode are joined at the cathode of one and the anode of the other. .

7.    HARDWARE AND SOFTWARE REQUIREMENTS

• R1 - 100K 1/4W Resistor
• R2 - 3K9 1/4W Resistor
• R3 - 1M 1/4W Resistor
• C1,C2 - 100nF 63V Polyester Capacitors
• C3 - 220μF 25V Electrolytic Capacitor
• D1 - LED Red 10mm. Ultra-bright
• D2 - 4148
• Q1 - BC547 45V 100mA NPN Transistor
• IC1 - 7555 or TS555CN CMos Timer IC
• L1 - Sensor coil

B1 - 1.5V Battery (AA or AAA cell etc.)

8.    PCB LAY OUT

9.     PCB FABRICATION

The PCB manufacturing process involves use of expensive equipments, but homebrew PCB fabrication is less expensive .It requires Intel Pentium PC,600-1200dpi laser printer with premium-quality paper or butter-paper and miscellaneous items like single side copper laminated board, Lacquer thinner, sand paper and others. The various steps involves in PCB fabrication are

                                    10.1. PC-based artwork

                                    10.2. Printing on a laser jet printer

                                    10.3. Transfer of pattern to copper plate using cloth iron

                                    10.4. Etching and Drying

                                    10.5. Drilling and cleaning

                                    10.6. Caution

9.1 PC BASED ARTWORK

            The PC based artwork consists of drawing the conductor pattern. For putting artwork on the component side of the board, flip the whole image before or while taking the print. When the pattern has been drawn, take the print out in 600 to 1200 dpi on a translucent or butter   paper. Keep the paper side on which the toner is deposited facing down over the copper laminated boards copper side and then when the board is turned component side up, the pattern on the conductor will be found properly aligned with the components. Finally we take the printout of the PCB.

9.2 TAKING THE PCB LAYOUT PRINT USING A LASER PRINTER

Take the printout of the circuit layout from a laser printer. The idea is to use a coated paper so that the toner comes loose when heated which would transfer a sharp black print on to copper laminate. Print for each of the required layers should be taken on separate paper.

                                                                                    

9.3 TRANSFER OF THE CONDUCTOR PATTERN

Scrub the copper side of the copper clad laminated used for the PCB board with a sponge. The scrubbing involves removes oxidation, stains, etc. And it also makes the copper surface some-what rough which helps the toner to adhere to the copper surface. The next step is to degrease the board thoroughly using a paper towel soaked with acetone solvent. Keep doing it until no more discoloration is seen on the paper towel. Rub hard and keep switching to clean parts of towel. Place and align the paper on the copper side, using an iron box to maximum setting on the back of the paper for at lest half a minute. If you don't apply enough heat, the film or toner may no stick or be dark enough. The removal of paper from PCB is done by putting it into hot water for 10 or more minutes. Check whether it has transferred properly onto copper plate.

Dig the bristles on the tip of a smooth tooth brush into the holes, remove the paper part from the tight areas like drill-holes. Now cut the PCB to required size by using a hacksaw.

9.4 ETCHING

Etch the unwanted copper from the board using the ferric chloride solution for 20 or more minutes. One pint can etch at least 3.6 sq. meters of the 28gm board. Heating the etchant will speeds up the etching process. The PCB is attached to a wooden piece and dip in to the solution. Lift the PCB up and Check whether all the unwanted copper is removed. Then it is immersed in to cold water to clean. When etching is complete, board is removed from the solution and rinse it under running tap water .Acetone or lacquer thinner is used to remove the toner .Lacquer thinner is used as a solvent in painting industry. Wash the board in lacquer thinner solvent, rubbing with a paper towel, to remove the toner instantly.

9.5 DRILLING AND CLEANING  

In this we had used a PCB hand drill .Use 0.8mm PCB drill bit to drill out all of the component holes. After drilling the holes scrub sponge is used to clean before soldering .After drilling and cleaning, wash the board in cold water and then dry it.

9.6 CAUTION

Lacquer thinner is extremely volatile, inflammable and explosive .Acetone can irritate eyes and respiratory system .Ferric chloride is corrosive, so avoid skin and eye contact.

10.  SOLDERING

          Soldering is the process of joining metals by using lower melting point metal to wet or alloy with the joined surfaces. Solder is the joining material. It melts below 427’C. Soldered joints in electronic circuits will establish strong electrical connections between component leads. The popularly used solders are alloys of tin and lead that melt below the melting point of tin.

In order to make the surfaces accept the solder readily, the component terminals should be cleaned chemically or by abrasion using blades or knives. Small amount of lead coating can be done on the cleaned portion of the leads using soldering iron. This process is called tinning. Zinc chloride or ammonium chloride separately or in combination are the most commonly used fluxes. These are available in petroleum jelly as paste flux. A solder joint can at first glance to be okay, but under close examination it could be a ‘Dry Joint’. A dry joint is when either the circuit board or the leg of the component has not been properly heated to allow the solder to flow between the surfaces freely. This creates an intermittent or no electrical connection. This can also be caused by a lack of flux or if you reuse old solder.

            Quite often, reheating a bad join will cure the problem but in a lot of cases, the old solder will need to be removed and some new solder applied. The residues, which remain after the soldering, may be washed out with more water, accompanied by brushing.

Soldering iron is the tool used to melt the solder and apply at the joints in the circuit. It operates in 230V mains supply. The iron bit at the tip of it gets heated up within a few minutes. 50W and 25W soldering irons are commonly used for soldering purposes.

Procedure

1. Make a layout of the circuit.
2. Straighten and clean the component leads using blade or knife. Apply a little flux on the leads. Take a little solder on soldering iron and apply the molten solder on the leads.
3. Mount the components on the PCB by bending the leads of the components using nose-pliers.

Apply flux on the joints and solder the joints. Soldering must be done in minimum time to avoid dry soldering and heating up of components. Wash the residue using water and brush.

11.  TESTING

The circuit is connected to a mobile phone. Then a call is made to the phone. The phone is in silent mode. it is found that the led in the circuit glows indicating an incoming call.

12.  ADVANTAGES

·         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

·         This circuit can be used to escape from the nuissance of Mobile phone rings when you are at home.

·         Stand-by current drawing is less than 200µA, therefore a power on/off switch is unnecessary

·         Less cost

·         Small size

·         Easy insulation

13.  DISADVANTAGES

·        It has limited application if the distance between the circuit and cellphone increases

·        It is difficult to detect  when more than one phone is kept within the limited range of the circuit

·        Less efficient         

14.  APPLICATIONS

             This circuit can be used to escape from the nuisance of Mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated.

            Phones with this circuit can be used in places where vibration of phone  while in silent mode is a problem. For eg;while attending a business meeting, or while in a library etc the above mentioned matter is a problem,nder such sitations,this facility is of great help.

15.  CONCLUSION

            Our project cellphone calling detector finds many applications in our day to day life.using the basic theory behind the working of this circuit can be applied for implementing improved version of cellphone tracking circuits.  Even though this project is having limited application,its scope is wide. So hereby we once again thank everyone who contributed directly or indirectly in the success of our project Summary

            All in all then, for such a simple easy to make device I hope you agree that there is a lot of scope for interesting science / technology investigations with your mobile phone. The device would make a good science week project (for radio amateur clubs etc.) A 'deluxe' pcb version (Fig. 5) on a perspex display case (Fig. 5) is currently going around the southern UK as part of the SEPnet outreach work, see the 'Radiation Exhibition' [8] and also as part of my on-going lecture series [9].

16.  FUTURESCOPE

GPS TRACKING TECHNOLOGY,GPRS FACILITY ARE THE IMPROVED DEVELOPMENTS.IF WE ARE USING GPS TECHNOLOGY,THEN THERE ARE A COUPLE OF REQUIREMENTS THAT WE HAVE TO MEET.

·         The phone that we want to be able to track must be a smart phone.If your phone has the capability of downloading and installing apps onto it,then there is a pretty good chance that there is a tracking program that will work on it

·         You must subscribe to a data plan with your cellphone service provider in order for these apps to function

·         The app must be installed on the phone you wish to track before the need arise to use it

There are several FREE cellphone tracking applications to choose from these days.here are a list of the most popular free applications

·         Google latitude

·         Glympse

·         Instamapper

·         Buddy way