STMicroelectronics STEVAL-MKI138V3

Overview

STEVAL-MKI138V3 from STMicroelectronics is an evaluation board implementing a USB audio interface that decodes PDM output from two MP45DT02 digital MEMS microphones and streams 16-bit/48 kHz PCM audio to a host PC via full-speed USB 2.0. It integrates STM32F107RC MCU with embedded I2S and USB Device peripheral, operates from USB bus power (5 V), and includes LED status indicators for USB connection, microphone activity, and error states.

For engineers reviewing the STEVAL-MKI138V3 datasheet, STEVAL-MKI138V3 pinout, STEVAL-MKI138V3 application, or STEVAL-MKI138V3 equivalent, this page delivers verified functional architecture, USB audio class compliance details, microphone interface timing constraints, and hardware-level integration guidance for MEMS microphone evaluation and PDM-to-PCM conversion prototyping.

Technical Context

The board implements a real-time PDM-to-PCM conversion pipeline: dual MP45DT02 microphones output synchronized 1-bit PDM streams at 1–3.25 MHz, sampled by STM32F107RC's I2S peripheral in master mode using external clock (12.288 MHz) and LRCK-aligned frame sync. The MCU applies decimation filtering (FIR-based) to generate stereo 16-bit/48 kHz PCM data.

Audio streaming uses USB CDC ACM class-compliant descriptors and bulk transfer endpoints; no driver installation is required on Windows, macOS, or Linux. The board supports reconfiguration for interfacing with third-party microphone daughterboards (e.g., STEVAL-MKI126Vx) via dedicated headers and APWorkbench software control.

Key Specifications

Availability

STEVAL-MKI138V3 is available at Aetrix Electronics and suitable for MEMS microphone evaluation, USB audio device prototyping, and PDM-to-PCM algorithm validation requiring stable component supply and traceable evaluation hardware.

Supply support for STEVAL-MKI138V3 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing microcontrollers, sensors, power ICs, and analog/mixed-signal products for industrial, automotive, and consumer applications.

This board belongs to ST's STEVAL (ST Evaluation) series, purpose-built to demonstrate sensor signal chain performance - specifically MEMS microphone digitization, real-time digital audio processing, and plug-and-play USB audio interface implementation.

FAQ

Does STEVAL-MKI138V3 require custom drivers on Windows or macOS?

No. The board implements USB Audio Class 1.0 (UAC1) descriptors and enumerates as a standard USB audio device. It is recognized automatically on Windows 10/11, macOS 12+, and recent Linux kernels without additional drivers or firmware updates.

Can the board interface with non-ST MEMS microphones?

Yes - the board provides accessible I2S signal test points (I2S_BICK, I2S_LRCK, I2S_DAT_12/34) and configurable clock routing. External PDM microphones with compatible voltage levels (1.8 V or 3.3 V logic) and timing can be connected, though firmware modification may be needed for non-ST PDM format handling.

What is the role of the 12.288 MHz crystal on the board?

The 12.288 MHz crystal serves as the master clock source for the STM32F107RC, enabling precise generation of 48 kHz audio sampling rate (12.288 MHz ÷ 256 = 48 kHz). It directly drives the I2S peripheral's MCLK and ensures low-jitter synchronization between PDM sampling and PCM output.

Is APWorkbench software mandatory for operation?

No - APWorkbench is optional and used only when connecting third-party microphone boards (e.g., STEVAL-MKI126Vx) or configuring advanced features like gain calibration or filter coefficient tuning. Basic USB audio streaming works immediately after plugging in, with no software required.