My second Pi hacking project: a noise monitor. The setup uses a 7-segment, 4-digit LED backpack from Adafruit, a red LED, USB mic and some clever/simple Python code.
Ambient noise is measured from the USB mic via a python ALSA interface. The measured level is displayed on the LED screen (up to 4 digits). Measurement is done in 0.01 second intervals, but the display only changes when a set threshold and time is exceeded. When the noise exceeds a set point, the red LED lights to indicate a noisy environment.
Setting up the 4-digit display was amazingly simple. Seriously. One only has to buy and soldier the backpack (leaving the heavy work to Adafruit), connect it to the Pi and call set_digit() from python to change the display state. Amazing.
It truly is. The Pi and ready-made components and tutorials enabled me to go from zero to this in just under a day of continuous learning.