Cell Phone Controlled Audio Mute Switch

1
Cell Phone Controlled Audio Mute Switch

• Group 14
• Vivek Patel, Kavita Nagpal, Baldwin Yeung
• ECE 445 Senior Design
• November 30, 2005

2
Introduction

• This circuit detects the EMF radiated from a cell
  phone using inductors.
• The circuit automatically disconnects power
  supply to the audio system whenever a call is
  received or made by the cell phone.

3
Benefits and Features

• Benefits
• No calls can be missed.
• Safety issue concerning distractions while
  driving.
• Features
• Used inductors to detect the field emitted by the
  phone receiver.
• Used an LED detector to determine displacement of
  the phone from holder.
• Disconnection of the power supply to the audio
  system by the mute switch.

4
(No Transcript)
5
Circuit Overview

• Cell Phone Casing
• Cellular Phone Calling Detector
• Audio Mute Switch

6
Cell Phone Casing

• LED1 ? audio device is ON
• LED2 ? audio device is ON
• LED3 ? determines if cell phone is in the casing

7
Cellular Phone Calling Detector

• L1 ? detects EMF
• C1 ? by-passing, filtering, timing, interference
  suppression
• Q1 ? amplifies the detected signal
• D2 ? drives the LED
• 7555 ? used in monostable mode

C1
L1
D2
Q1
8
555 Monostable Mode

• When a pulse (or when a falling edge) occurs at
  the trigger input, the capacitor charges and the
  output pulse begins.
• Time tW 1.1RC

9
Audio Mute Switch
10
Tests and Results
Motorola V551

• Phone off ? voltage across L1 16.2 mV
• Minimum required voltage to activate circuit ?
  (2/3) Vcc ? 3.33 V
• Less sensitive after 6 cm ( voltage lt 3.33V)

11
Tests and Results
LG 4050

• Less sensitive after 7 cm ( voltage lt 3.33V)
• Thus, LG 4050 (being an older phone) emits more
  EMF compared to Motorola V551

12
Waveforms

• Phone off

13
Waveforms

• Phone at a distance of 0cm from L1

14
Waveforms

• Phone at a distance of 1 cm from L1

15
Waveforms

• Phone at a distance of 6 cm from L1

16
Achievements

• Audio mute was activated in a timely fashion.
• Audio mute circuit is activated even when the
  cell phone is in silent or vibrate mode.
• Cell phone detector operated as expected.

17
Challenges

• Audio remained turned off for only 3-5 seconds
  when the phone rang.
• Low sensitivity with greater distances from L1.
• Couldnt design the casing due to time
  constraint.

18
Amount of EMF

• SAR-Specific Absorption Rates of Radiation
• FCC limits phones to 1.6 Watts per Kilogram

19
Future Enhancements

• Increase sensitivity
• Noise Interference?
• Compact Design?
• Ambient Light Interference?
• Cost effective (ones available in the stores are
  150 200)
• Use more amplification to get higher sensitivity
  from even smaller signals

20
Credits

• Professor Swenson
• Professor Bernhard
• TA Ishaan Gupta
• Saul Lipton
• ECE Parts Shop

Thank You