Simple Mobile Phone Detector Circuit using Transistors

Think you have a secret agent gadget that can sense nearby cell phones.

Mobile Phone Detector circuit acts like a listener for special radio waves phones use to talk to towers.

It can even pick up on these signals before the phone rings kind of like catching a secret handshake between the phone and the tower.

It uses transistors, tiny electronic switches to detect these special radio waves.

Circuit Working:

Parts List:

This circuit picks up the radio waves RF when a phone is initiating a call.

It detects the signal exchange between the phone and the cell tower during the connection setup even before the phone ring.

The key component is a special diode OA79.

It is much more sensitive than a standard diode 1N4148 allowing the circuit to detect the signal from a further distance.

This circuit is great for comparing different diodes.

It lets you see how the sensitivity of the diode affects the detection range.

Here is how circuit works:

The first transistor is always turned on.

When the phone initiates a call the coil picks up the RF signal and creates a tiny voltage swing.

This voltage change briefly reduces the voltage, at the capacitor and the transistors base.

This slight change gets amplified by the transistors ultimately turning on the LED.

The more sensitive OA79 diode allows the circuit to detect the phone signal from a distance of one meter compared to only 10 centimeters with a regular diode.

The circuit itself uses very little power around 1mA.

Formulas:

Using numerous transistors to obtain high gain and sensitivity is necessary when building a cascaded darlington transistor stage for a mobile phone detector circuit.

This is a simple overview of how to create and comprehend a circuit of such kind:

Current Gain (β)

For a single stage: β_total​ = β_Q1​ × β_Q2​

where,

• βQ1 and 𝛽Q2 are the current gains of transistors Q1 and Q2, respectively.

Using cascaded BJT darlington stages, this formula offers a fundamental knowledge and a place to start when developing a mobile phone detector circuit.

Depending on the particular circuit needs and the surrounding circumstances, more thorough calculations and changes can be needed.

How to Build:

To build a Simple Mobile Phone Detector Circuit using transistors follow the steps mentioned below for assembling the components:

• Connect the emitter of transistor Q1 to ground.
• Connect the base of transistor Q1 to capacitor C1, D1 diode and antenna in series.
• Connect the collector of transistor Q1 to positive supply through resistor R3.
• Connect inductor coil one end to base of transistor Q1 and other end to ground.
• Connect the emitter of transistor Q2 to ground.
• Connect the base of transistor Q2 to resistor R4 and capacitor C2.
• Connect the collector of transistor Q2 to resistor R5.
• Connect the emitter of transistor Q3 to ground.
• Connect the base of transistor Q3 to collector of Q2 and resistor R5.
• Connect the collector of transistor Q3 to positive supply through resistor R6 and Red LED.
• Connect a series of resistors R1 and R2 from positive supply to ground.
• Connect a push button to positive supply of 3V battery.

Safety Note:

• Always follow basic electronic safety practices.
• Avoid touching live components while the circuit is powered on.
• In some regions, using circuits to detect phone signals might violate privacy laws.
• Check local regulations before building or using such a detector.

Conclusion:

Transistor based mobile phone detector circuit offer a simple way to detect basic phone activity.

However, their range is limited effectiveness varies with network technology and they might pick up interference.

Remember to prioritize safety during construction and be aware of potential legal restrictions in your area.

References:

Schematic circuit of the cell phone detector