User manual
UM1900
Hardware description
DocID027905 Rev 1
5/15
3 Hardware description
The board allows the user to test the function of the STMicroelectronics MEMS
microphones. For this purpose two MP34DT01-M digital MEMS microphone are mounted
on the board and 6 headers (4 mounted with 2 additional footprints) are available for
connecting additional microphones using digital microphone coupon boards (STEVAL-
MKI129Vx or STEVAL-MKI155Vx), for further information refer to www.st.com. The
connection between the X-NUCLEO-CCA02M1 and the STEVAL-MKI155V1 is shown in
Figure 3: "Connection with STEVAL-MKI155V1". The board interfaces with the STM32
Nucleo microcontrollers via the I²S and SPI peripherals for the synchronized acquisition of
up to 4 microphones. The board also provides USB streaming using the STM32 Nucleo
microcontroller USB peripheral; for this purpose, a USB connector is available as well as
the footprint to mount a dedicated oscillator that can be used to feed the host MCU through
the OSC_IN pin. Solder bridges are used in order to choose from different options,
depending on the number of microphones and the MCU peripherals involved.
Figure 3: Connection with STEVAL-MKI155V1
3.1 USB connector and power source
A USB connector available on the board supports audio streaming to the host PC. It can
also be used to power the whole system, Nucleo board included. To enable system power
sourcing from the X-NUCLEO-CCA02M1 expansion board USB connector:
close Jumper J1 on the X-NUCLEO-CCA02M1 expansion board
place JP5 in position E5 on the STM32 Nucleo board
3.2 Audio acquisition strategy
A digital MEMS microphone can be acquired by using different peripherals, such as SPI,
I²S or GPIO. It requires an input clock and it outputs a PDM stream at the same frequency
of the input clock. This PDM stream has to be filtered and decimated in order to be in the
standard PCM audio format. Two different digital MEMS microphones can be connected on
the same data line by configuring the first to generate valid data on the rising edge of the
clock and the other on the falling edge by setting the L/R pin of each microphone
differently. On the X-NUCLEO-CCA02M1 expansion board, two microphones share the
same data line and are routed to the Nucleo STM32 I²S peripheral (the first and the second
microphone) and SPI peripheral (the third and the fourth).