Introduction
The article discusses a circuit design that can automatically mute a car amplifier when it detects a cellphone call, making it possible to mute the amplifier without manual intervention.
The Problem
Listening to loud music while driving can be enjoyable but becomes a nuisance when a phone call comes in. An automatic muting system that identifies a cellphone call and mutes the car amplifier immediately can save the user from turning off the music manually.
The Solution
Cell phones produce a significant amount of radio frequency (RF) every time they receive or make a call. This makes it possible to detect the functional status of a cellphone using the RF it emits. The following circuit demonstrates a basic RF sniffer or detector circuit that can be integrated with a car amplifier to mute the music whenever a call is received or made.
Hardware Required
You will require the following hardware for the cell phone RF-triggered car Amplifier Circuit.
| S.no | Components | Value | QTY |
|---|---|---|---|
| 1 | IC | A1, A2 | 1, 1 |
| 2 | Polar capacitor | 100uF / 25v | 1 |
| 3 | Non polar capacitor | 0.1uF | 2 |
| 4 | Resistor | 2m2, 10k, 100k | 2, 3, 2 |
| 5 | Diode | 1N4007, 1N4148 | 1, 2 |
| 6 | LED | – | 1 |
| 7 | Transistor | BC547 | 1 |
| 8 | Relay | 12V / 2amps | 1 |
Circuit Diagram
The circuit design consists of an RF sensor and a relay driver stage. The RF sensor consists of A1 and A2, which are high-gain amplifiers linked in series for maximum sensitivity. The feedback resistor 2M2 determines the gain or sensitivity level of the op-amps. The op-amps together can detect all kinds of RF signals specific to the local area.
In a car, there may be multiple disruptions apart from the cellphone RF, so the sensitivity must be set optimally to detect only the RFs from the cellphone and not from the vehicle’s ignition system. Multiple circuit units can be placed in various corners of the car interior, and the outputs can be integrated with the main relay driver so that the receiver can sense the RFs from all over the interior, including from the passengers’ cellphones in the rear seats.
Working Explanation
When a cellphone is initialized with a call, the RFs are detected by the circuit’s antenna and transformed into an amplified DC that changes with the cellphone’s emission levels. The amplified output across A2 is filtered by a diode and capacitor network and used to drive the relay stage. The relay clicks and switches ON the mute terminals of the car amplifier, causing the music to turn off until the call is finished.
Final Words
You can integrate this circuit design with a car amplifier to mute the music automatically when a cellphone call is received or made. Try out this circuit, and let us know how it works for you. Happy building!
