For our guitar tuner, our group elected to utilize an Elegoo Uno, an LCD screen, and a microphone amplifier with adjustable gain. The circuit diagram for our guitar tuner can be seen below.
The microphone we purchased has an Op Amp built in that we can manually adjust the gain to. The microphone will take in the sound played by a guitar, then output a voltage signal that the Elegoo reads and then associates with a fundamental frequency. After associating this signal with a fundamental frequency, the Elegoo associates the frequency with a string and outputs the name of the string on the LCD screen. Below is a picture of our circuit hooked up.