Adafruit PDM MEMS Microphone Breakout

Adafruit PDM MEMS Microphone Breakout is an exotic new microphone and the "third" kind of microphone that can integrate with electronics, apart from analog or I2S. The Pulse Density Modulation (PDM) microphone is commonly used in products, but rarely seen in maker projects. The sensor doesn't provide an "analog" output like many electret microphone assemblies making it great for chips without analog inputs.

The PDM has a very simple digital interface but it's not PWM or I2S, so the chip has to have a PDM interface. Most 32-bit processors available do. PDM is a little like 1-bit PWM. Clock the mic with a 1-3MHz clock rate, and on the data line to get a square wave out that syncs with the clock. The data line with be 0 or 1 logic output, with the square wave creating a density that when averaged will result in the analog value out.

DESIGN SUPPORT

• There's a few ways to manage these mics:

• (Ideal) Chip comes with a hardware peripheral and library that does all the data managing at high speed, collects samples, applies a filter and gives an analog value.

• Chip comes with a hardware peripheral that gives values, then it's up to you to perform the decimation/filtering. 
  (Adafruit offers example code for this on the ATSAMD21 chipset)

• Chip does not come with a hardware peripheral but you're able to come up with a way to make it work.

• (A hack, but works!) You generate the high speed clock, then add an analog filter on the data line, and read the analog value