Sound into Light shows

Step 3 Filter circuit

I used the PDF titled "Op Amps for Everyone" by Texas Instruments to learn how to make a band pass filter. Specifically i used the Sallen Keys band pass filter located in section 16.5.1.1

The op amps i used were LM358N, which are dual amps. this was very nice when i was putting my circuit together since i only had to use 2.

I chose this specific circuit because of its simplicity. The formula’s to select a frequency, quality (bandwidth) and gain are pretty simple in comparison to others but you pay for it since gain and quality are interlinked. Since this was my first attempt at making a band pass filter, i chose simple over versatile. I selected 110hz, 440hz and 1760 hz as the target freq’s for my filters. I’ve also included a simple spread sheet i made so you can select the frequency you want to tune your filter for by adjusting the capacitance and resistance of the circuit.

The bare minimum of space needed on your bread board is 10 rows. if you chose to spread your circuit out (which i advise during initial building and testing) just adjust accordingly when i mention a specific row.

Since i already used one side of the first op amp for the amplification circuit, i used a different bread board layout for each one. First i'll cover the other side of the op amp i used for the amplification circuit.

I place my chip with pins 1 and 8 on row 6. Refer to the microphone step to find out how to find which pin is which. This will put the eventual input of the filters closer to the amplification circuit.

(include picture here)


Now for the other op amp layout.