Expanding The Audio Features of Raspberry Pi Using This Device


  • CML Microcircuits has introduced an evaluation board for its low-power voice codec based around a  Raspberry Pi
  • The codec, the CMX655D, has been built into the EV6550DHAT – a board compliant with Raspberry Pi’s HAT (hardware attached on top) extension board standard

HAT stands for “Hardware attached on top”. It is a new hardware specification for add-one modules for the new Raspberry Pi model B+. HATs have several advantages compared to older add-on modules for the Raspberry Pi. It features a robust and solderless design. It is designed in concern with plug n play devices. It also features an auto configurable state which helps in easy integration of the module with Raspberry.

Pi Hat module for audio interfaces

CML Microcircuits has introduced an evaluation board for its low-power voice codec based around a RaspberryPi. According to the company, the module integrates the entire signal chain from dual matched digital MEMS. The microphone interfaces to a 1W Class D speaker driver. It incorporates decimation, filtering, signal processing and digital gain of the device. It is supported by an I2S/PCM audio interface and SPI control interface. It represents a single-chip, low power solution to add advanced voice coding/decoding to any application.

Power consumption up to nine milliwatt


On the power consumption, the module works at a current consumption of less than 220 µA (stand-by, the main clock enabled). The total output power is measured to be 9mW(when line driving). When the module is not in use, the recording mode consumes a current of up to 500μA.

Interface using 40-pin GPIO connector

This evaluation HAT is compatible with any Raspberry Pi. It is connected using a 40-pin extended GPIO connector (almost all). The module is powered by the Raspberry Pi. External supply can be applied to the system if all the connected peripherals are able to limit the power consumed through the USB device.

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Determining the audio quality of the system

The evaluation board features access to pre-recorded sample files. It provides an ability to record and playback audio files in the .wav format. This helps in analysing pre-recorded samples at different rates and levels. It is helpful in determining the audio quality of the system. The board also includes configurable parameters to trim sample rate (8, 16, 32 or 48ksample/s), volume and level (dB) of the audio signal.

An official from CML talked about the product saying,

The Raspberry Pi single-board computer is widely recognised by makers, enthusiasts and professional developers as the platform of choice for rapid hardware and software development. The EV6550DHAT builds on this growing ecosystem by bringing CMX655D voice codec to the Raspberry Pi community.


The board features an interactive graphical user interface(GUI). It allows the audio input to gain from -12dB to +3dB. It also supports functions like smoothing and muting.

Raspberry pi supports dual-mode features. It fulfils the requirement of a microcontroller as well as a microprocessor. This new module Hat can help in the design and development of complex problem-solving devices related to audio interfaces.




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