Mic Controlled LED Visualizer Using LM3914 Explained

In this project, I will create a simple LED volume meter. Sound received from the environment is converted to light signals. The main parts of this circuit are:

> The condenser mic: It converts the sound detected from the environment to low-voltage signals.

> LM358: An op-amp that is connected in inverting amplifier configuration to amplify the low-voltage signal from the mic.

> LM3914: it shows variations in 10-bit mode. Which means it can visually show the voltage strength by lights.

I have divided the circuit into different portions and tried to explain them visually in this article. hope you will enjoy it!!

List of tools needed:

1 x 9V battery

1 x 10k resistor

2 x 100k resistor

2 x 0.1uF capacitor

3 x 1k resistor

1 x 47k variable resistor

1 x condenser mic

1 x LM358 op amp

1 x LM3914 10-bit comparator

10 x LED's

Proteus 8 pro software

Few connecting wires

This is basically a very simple visualizer.

If you like direct action like me then skip all the theory parts :))

As you can see from the diagram it contains mainly 5 blocks. The input block contains a mic that produces millivolt signals which are passed on to a high-pass filter. It filters the noise and sends filtered data to the amplifier to boost the signal. Finally, this signal is sent to a comparator that runs several LEDs on the output.

Details of the blocks are given below.

The mic is connected in series with the power source. It can generate a voltage on the output with sound. The voltage produced by the microphone is very low so it requires an amplifier circuit to amplify its level. A pull-up resistor in the range of kilo-ohm is used to supply power to the built-in FET impedance converter.

A high pass filter allows a high-frequency signal to pass but blocks a low-frequency signal. It is done by adding a resistor and capacitor. The cut of frequency can be calculated using the following formula: F = 1/ (2πRC). This means in our circuit the cut-off frequency is around 16Hz. So any signal at 16Hz or below will not pass. As you can see from the diagram, the higher frequency can easily pass but the lower frequency is highly attenuated.

This is necessary to remove the background noise. Since our audible range of humans is 20-20000Hz, this filter makes the circuit more accurate.

I have added the simulation file Here

The signal from the mic is very low to be detected by the comparator IC. Thus it needs to be amplified. Here a non-inverting amplifier with a gain of 100 is being used to amplify the signal.

As you can see in the example from the animation, if the resistor values are 10k and 1k then the amplification would be 1+(10/1) = 11 times.

I have added the simulation file Here

Above is a diagram of the LM3914's internal circuit. LM3914 is essentially a synthesis of ten different comparators. They are basically op amps with gain in reference voltage. The value of reference voltage can vary and thus we have to use a 47k variable resistor.

The variable resistor can be used to control the sensitivity of the circuit.

I have added the simulation file Here

I have used proteus to complete the simulation, I have replaced the mic with an AC voltage source since the software would shut down each time I try to run the simulation. This mic can receive a signal from your laptop/PC mic and show the output. So, if your computer can handle the load you can change it to a mic and run the simulation.

I have added the final simulation file Here

I have used the built-in functionality of Proteus to build the schematic. The 3D diagram looked really nice. I have added all the files in a google drive folder.

Download the full file from here: Download

I will utilize PCBWay's services, the sponsor of this Instructable, to produce the circuit board.

In order to order from PCBWay we need to convert the design we just created into Gerber format. This process is quite simple. I would highly suggest you watch the video from ElectroTechCC to learn how to create a Gerber file. LINK

After clicking on the option to add the order to the cart, a popup appeared prompting me to provide the Gerber files we had exported. Consequently, I created a zip file containing all the exported files and selected that zip file for upload.

I placed an order for 10 boards and the cost was only $5, so per board only costs 50 cents only. Now that's cheap.

And you are done with the project. The finishing of the boards is quite nice. After soldering the components and connecting the board with the power supply (4V - 6V) everything worked perfectly.

Thank you for reading and I hope you learned something. Cheers!!