Imagine we have a spy device that finds nearby mobile phones.
Mobile Phone Detector Circuit using Transistors is like ear for special signals phones send to towers; it can catch signal even before phone rings like secret talk between phone and tower.
Also, it uses transistors, small switches to catch these signals.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 1M, 10k (1/4 watt) | 2 each |
| 470k, 220 (1/4 watt) | 1 each | |
| Capacitors | Ceramic 10nF | 2 |
| Semiconductors | Transistors 9018 | 3 |
| Diode OA79 | 1 | |
| LED Red 5mm, 20mA | 1 | |
| Inductor 13 turns using 1mm thick wire, 5mm diameter | 1 | |
| 30cm Antenna | 1 | |
| Push button | 1 | |
| Battery 3V | 1 |
This circuit catches RF signal when phone start a call, it sense signal between phone and tower before phone ring.
Main part is special diode OA79, it is more sensitive than normal diode 1N4148 so it can catch signal from far.
Furthermore, it is good for testing different diodes, by showing how diode sensitivity change the range.
How circuit work:
First transistor is always ON and when phone call start coil catch RF and make small voltage change.
This drop voltage at capacitor and base of transistor and this transistor boost this small change and turn ON the LED.
OA79 diode can catch phone signal from 1 meter, whereas normal diode catches at only 10 cm.
Hence, this circuit use very low power which is around 1mA.
Formulas:
To make circuit more sensitive use many transistors in chain like Darlington pair.
Current Gain (β):
For two transistors:
βtotal = βQ1 × βQ2
This help understand how to make phone detector using Darlington stage and we can change design based on what circuit need.
How to Build:
To build a Mobile Phone Detector Circuit using transistors follow the steps mentioned below for assembling the components:
- First, connect the emitter of transistor Q1 to ground, connect the base of transistor Q1 to capacitor C1, D1 diode and antenna in series and then connect the collector of transistor Q1 to positive supply through resistor R3.
- Next, connect inductor coil one end to base of transistor Q1 and other end to ground.
- After that, connect the emitter of transistor Q2 to ground, connect the base of transistor Q2 to resistor R4 and capacitor C2 and then connect the collector of transistor Q2 to resistor R5.
- Then connect the emitter of transistor Q3 to ground, connect the base of transistor Q3 to collector of Q2 and resistor R5 and then connect the collector of transistor Q3 to positive supply through resistor R6 and Red LED.
- Now connect a series of resistors R1 and R2 from positive supply to ground and then lastly, connect a push button to positive supply of 3V battery.
Safety Note:
- Always be careful, do not touch wires when power is ON.
- In some places using this kind of circuit may not be legal, so check our area rules before using these type of circuit.
Conclusion:
To conclude, this Mobile Phone Detector Circuit using Transistors is easy to build, as it can find phone activity but only in short range.
Also, it may not work same with all networks and it can also get wrong signals; hence, while making the circuit be safe and follow the rules in your area.