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  • Author Author: amgalbu
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MagicHat - 15 - Let's MagicHat speak

amgalbu

After finishing the data acquisition part of the project, let's see how to make the MagicHat a little more... magic

 

To make Arduino Yun speak, I first need an external USB audio card like this one here

 

image

 

Then, I need to install an mp3 player that will play a file stored on SD card. Installing the mp3 player is just a few packages away...

 

opkg update
 opkg install kmod-sound-core 
 opkg install kmod-usb-audio 
 opkg install madplay

 

Since the control logic runs on the Atmel side of Arduino Yun, we need to devise a way to launch the player. To send data from Atmel to Linino I disabled the bridge, so now Serial1 is read by NodeJS.

So, the firmware running on Atmel will send out (by calling Serial1.println) a string like

 

PLAY helloworld.mp3

 

and NodeJS will launch the mp3 player to play to "helloworld.mp3" file

 

This can easily achieved using the NodeJS's 'exec'  package

 

var exec = require('child_process').exec;
exec('/usr/bin/madplay ' + filename);

Parents Comment Children
  • in reply to amgalbu

    I was thinking that there would be something that told the player that sound should play though the USB. I'm not an expert on how drivers work on Linux systems but there must be something that does the internal "wiring" so that it can work with multiple  sound devices.

  • in reply to Workshopshed

    Hi clark

    Looking at the price of the usb sound card (2.21 euros on amazon, shipping included), I imagine that the usb card is really stupid. I think the mp3player and linux drivers do all the decoding works and sends out on usb a stream of pcm data (on in any way another uncompressed format)

    In case of multiple sound devices, a parameter should be added on the madplay command line to select the desired device.

     

    Cheers

    Ambrogio