Description

Adafruit MEMS Mic Breakout

PDM is the 'third' kind of microphone you can integrate with electronics, apart from analog or I2C. These microphones are very commonly used in products, but are rarely seen in maker projects.

The first thing to note is that this sensor does not provide an 'analog' output like other microphone assemblies. It's great for chips that do not have analog inputs. Secondly, the digital interface is a very simplistic pulse density modulation output. It's digital but its not PWM and it's not I2C. You will need to make sure your chip has a PDM interface - most 32-bit processors do.

PDM is a little like 1-bit PWM. You clock the mic with a 1 MHz - 3 MHz clock rate, and on the data line you'll get a square wave out that syncs with the clock. The data line will have a 0 or 1 logic output, with the square wave creating a density that when averaged will result in the analog value out.

There's a few ways to manage these mics:

Your chip comes with a hardware peripheral and library that does all the data managing at high speed, collects samples, applies a filter and gives you an analog value
Your chip comes with a hardware peripheral that gives you values, then it is up to you to perform the decimation/filtering
Your chip does not come with a hardware peripheral
You generate the high speed clock, then add an analog filter on the data line, and read the analog value
Either way you decide to go, make sure you have a handle on what support you get with your platform, as these chips are a little tricky

Product Video

Quick Spec

Voltage Range: 1.8-3.3V
Clock rate: 1 - 3.25 MHz
Current draw: 0.6mA
SNR: 61 dB
Sensitivity: ~-26 dBFS
Dimensions: 14.0mm x 12.8mm x 2.8mm

Pinout

3V - This is the power input pin, this powers the chip directly. Use a quiet power supply pin if available (The chip supports 1.8-3.3V but we have not tested it at 1.8V)
GND - Power and data ground reference
SEL - Left/Right select. If this pin is high, the output is on the falling edge of CLK considered the 'Right' channel. If this pin is low, the output is on the rising edge, a.k.a 'Left' channel
CLK - PDM clock in, 1 - 3 MHz square wave required
DAT - PDM data out