Drum tuner

I was having problems when tuning my drums, so I made my self a drum tuner...

It's a small device that records sound sample immediately after hitting the drum and then it makes FFT analysis of that sound and searches frequency that has the highest magnitude. This device consists of a microphone, an amplifier, a micro-controller (STM32F1) and LCD display. Below is a schematic diagram of the system.

Tuner schematic

The signal from the microphone passes through the amplifier and low-pass filter (cutoff frequency  = 1 kHz) and then goes to the input of the a/c converter of micro-controller. Converter is set so that his sampling frequency is 2 kHz (double the measured frequency). Micro-controller starts the calculation after the amplitude of the sound reaches a certain level. After performing the calculations micro-controller displays the result on the LCD. Device also checks the battery status and displays its state immediately after starting. Writing software for this device I've used the CMSIS and DSP libraries for STM32 micro-controllers. 

Tuner board

Prototype board

Professional version of board 

Working board with mounted parts

Special grip to mount device on drum

Here's video of working device ;)