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Sensors, Actuators, and Robotics » sound recording module

March 31, 2011
by jasongillikin
jasongillikin's Avatar

I would like to record sound to play back, but all I can find are 20sec modules... anyone know of a 2 minute module (not partitioned, just flatout 2 minutes) for fairly cheap...

jason

April 04, 2011
by Hexorg
Hexorg's Avatar

I don't know about any sound recording module, but you can build one yourself with the nerdkit, Although a few more parts will be required.

First of all, you'd have to rewire ATmega's A/D converter to have Vref = to the maximum voltage in your audio signal. If you are recording from a microphone, you'd also have to use a little amplifier. (I think radio shack sells nice little op-amp based audio amplifiers).

I'm afraid uncompressed 2 minutes audio at 44.1KHz sampling frequency and 8-bit resolution will be 5.3 megabytes long, so I'd recommend getting either more RAM chips, or you can buy an SD memory-card (it can't be HCSD, just regular SD with capacity < 2.0Gb)

And then to play the audio back you'd need to get D/A converter. 8-bit is plenty for a great quality (that's what they use in computers to generate sound). If such a great quality is not required, you can get a lower-bit value D/A converter. Then D/A will be connected to the speaker (preferably with a little audio transformer in between)

From here's it'll be almost simple. Read the A/D at the frequency of 44.1kHz, since A/D in the nerdkit is 16-bit, convert that number to the amount of bits that the D/A has (just but right bit shifting), let's say D/A has n-bits. Save the resulting data to the memory card for recording. To play back, Read the SD card to a buffer, and output n-bits to D/A every (1 / 441000) seconds.

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