The board features an ARM Cortex-M4 microcontroller with audio file decompression software, a choice of high-end and low-cost DACs, a codec, and digital and analogue microphones. By using the board’s free PC-based graphical user interface, which connects to the board via USB, developers are able to start recording and playing back audio files in minutes. The board also provides a hardware environment in which to develop code and evaluate the performance of ARM Cortex-M4 application software.
At the heart of the new board is the MK60N512VMD100 microcontroller from Freescale, a member of the K60 Kinetis family of products. With the free MQX real-time operating system and a free USB stack pre-loaded on the microcontroller, the board provides a highly capable general platform for ARM Cortex-M4 development work. For system-level prototyping, it can be interfaced to Future Electronics’ LongBow Future-Blox motherboard. The board’s software uses the ARM DSP CMSIS library, which has been optimised for the DSP co-processor available on the ARM Cortex-M4 core – an attractive feature in applications such as motor control.
The specialist software and peripheral features on the Audio Streamer Micro-Blox make it suitable for the rapid development of digital audio equipment proofs-of-concept. Audio file decoding software embedded in the microcontroller can handle MP3, FLAC, WAV and Ogg Vorbis file types. FLAC, a ‘lossless’ file format, is becoming popular in hi-fi equipment in which excellent sound reproduction and very low distortion are of paramount importance.
Ogg Vorbis, by contrast, is an open-source, royalty-free file format that achieves tighter compression than MP3, and thus is used in embedded and industrial audio applications in which the emphasis is on reducing the requirement for memory. The powerful K60 microcontroller also has ample processing power to run other software for decoding files such as ALAC, WMA, AIFF and AAC. An Ethernet connection for file downloading is provided via the KSZ8031RNL, a small, low-power Ethernet transceiver from Micrel.
Audio playback of the decoded files is via one of two Wolfson Microelectronics DACs: the high-end WM8741 is intended for use with FLAC files for very high sound quality. The WM8741’s outputs are buffered by high-end quad audio op amps. The on-board power supply uses small and efficient buck and boost regulators from Micrel, but the board also provides a terminal block for the connection of an external audio-quality power supply.
The board’s other, lower-cost DAC, the WM8524, is suitable for use with Ogg Vorbis, WAV and MP3 files. It also includes three 3.5mm stereo sockets for connection to external speakers.
For highly integrated applications, Wolfson’s WM8904 ultra low-power codec is also available, offering an ADC, DAC, ReTune digital audio processing functions and headphone amplifiers. Two digital microphones and a single analogue microphone interface to the WM8904 for sound recording.
The board is intended as a proof-of-concept development platform, for use in early prototyping. For this reason, Future Electronics makes available all relevant design information including Gerber design files, schematics and bill of materials. This enables developers to readily modify and refine the design for different end products.