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Analog Noise Level Meter
Analog Electronics
A sound-level display using four cascaded LM3914 ICs and four LED bar graphs to create a 40-LED visual output.
Project
1.5
Input
Microphone
Driver
4 × LM3914
Display
40 LEDs
Enclosure
3D Printed
Project Context
The Analog Noise Level Meter was developed as a final project incorporating skills from the course. A microphone provides the input while four cascaded LM3914 ICs drive four LED bar graphs to display the level of sound.
Reference
01
Four cascaded LM3914 ICs drive four 10-LED bar graphs, creating a total visual output of 40 LEDs.
The proposal used a microphone as the input and four LED bar graphs driven by LM3914 chips as the output.
The report also describes a microphone or potentiometer providing input, displaying sound level for the microphone and resistance for the potentiometer.
02
The LM3914 senses analog voltage levels and drives up to 10 LEDs to create a linear visual output.
Each LM3914 has 18 pins. Pin 9 can switch the chip between bar and dot mode. The report lists an operating voltage of 3–35 volts and states that one LM3914 can drive up to 10 LEDs.
As voltage is input into the LM3914, its output pins are set high and the corresponding LEDs illuminate.
03
Inside each LM3914 are 10 comparators used to respond to changes in the input voltage.
A comparator compares two voltages or currents and outputs a digital signal indicating which is larger. It has two input terminals, V+ and V-, and one digital output, Vo.
In the LM3914, the report describes 10 comparators in parallel with 1 kΩ resistors separating them. As the input voltage increases, more comparators turn on.
04
Dot Mode
One LED High
In dot mode, only one LED is high while the remaining LEDs are low.
Bar Mode
LEDs Build Up
In bar mode, every LED up to the highest active level is high.
05 / Step 1
The circuit was designed around four LM3914 chips and four LED bar graphs.
Circuit Schematic
06 / Step 2
The schematic was transferred into a working breadboard prototype.
Wires were soldered onto the bottoms of the bar graphs, microphone, and buzzer to make wiring easier. The schematic was then followed and the components were connected.
Breadboard Prototype
07 / Step 3
The breadboard circuit was transferred to a solder breadboard to secure the components in place.
Small components, chip seats, and headers were soldered first, followed by larger components including the buzzer and LED bar graphs.
Soldered Circuit
08 / Step 4
The final circuit was housed inside a custom 3D printed enclosure.
The case was designed in Fusion 360 with the help of tutorials for precision measuring.
The case was sliced in Ultimaker Cura and printed on an Ultimaker 3+ Extended. The total print time was 4 hours and 25 minutes.
3D Printed Case
09
Parts Table
Qty.
9V DC Alkaline Battery
1
3mm Barrel Jack
1
LM3914 IC
4
LED Bar Graphs
4
1 kΩ Fixed Resistor
3
2.2 kΩ Fixed Resistor
1
3.3 kΩ Fixed Resistor
1
10 kΩ Potentiometer
1
Mic with Amplifier
1
LM7805 5V Voltage Regulator
1
Solder Breadboard
1
3D Printed Case
1
Heat Set Rivets
4
Screws
4
Buzzer
1
Slide Switch
1
Wires
Assorted
10
The completed Analog Noise Level Meter combines a microphone input with four cascaded LM3914 ICs and four 10-LED bar graphs to create a 40-LED sound display.
Analog Noise Level Meter
Completed project
40-LED Display
Four cascaded LED bar graphs