Decibel Level Detector Project

Chris LombardoIME 458

• Produce a decibel level detector with a range of 0-50 decibels

• Use a LM3915 integrated chip to drive a series of ten groups of LEDs

Objective

Circuit Diagram

BOMCount Ref Value Description Size Part # MFR

1 R1 10k Resistor   Std Std

6 R2, R3,R5, R7,R8, R10

100k Resistor   Std Std

1 R4 47k Resistor   Std Std

1 R6 1k Resistor   Std Std

1 R9 56k Resistor   Std Std

1 R11 4.7k Resistor   Std Std

2 R12,R14 100 Resistor   Std Std

1 R13 330k Resistor   Std Std

1 R15 220k Resistor   Std Std

1 R16 10 Resistor   Std Std

2 R17, R19 390 Resistor   Std Std

1 R18 22k Resistor   Std Std

1 P1 10k Log Potentiometer   Std Std

3 C1, C4, C8 330nF Capacitor      

1 C2 47uF/10V Capacitor      

2 C3, C9 100uF/10V Capacitor      

1 C5 100nF Capacitor      

1 C6 470uF/16V Capacitor      

1 C7 10uF/16V Capacitor      

1 IC1   MC33172P      

1 IC2          

1 5V Reg   Voltage Regulator   LM2931AZ5 TXS

20 LED   Red LEDS   MV8191 Everlight

1 Mic   Electret microphone   CEM-C9745JAD462P2.54R 

Challenge Electronics

1 Bat   9V Battery   Std Std

1 Switch   SPST switch   2FA5373TABS CARLING TECHNOLOGIES

Project Description

• Omnidirectional electret microphone serving as the input

• Two amplifiers with the first amplifying the signal and the second serving as a rectifier driver

• The Q2 transistor charges capacitor C8 and then discharges it across R13 to make a peak detector

• The Q3 transistor changes the sensitivity of the LM3915 chip giving the system an extra 20db of range

• The main component of the system is the LM3915 itself which controls the currents through the LEDs while also measuring the input voltage line SIG logarithmically with a range of 0-50db

Description Continued

After completing this project I have a fully functioning sound level reader with a range between 0-50db with steps of roughly 5db between each LED

Overall success but a board with dual LM3915s would be more useful.

Conclusion