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Re: Sound with Etrax
I've used a Winbond WTS701 Text to speech chip. They are dirt cheap.
It comes with a low power built in amplifier so it would probably be ideal
for speaking through the phone. I've not interfaced it to a Axis board
we interfaced this to an Atmel ATMega128 and it works very well.
The nice thing about going this route is that you only need to store text
menu strings and not whole voice samples so it can be customised easily.
The only thing you'll have to figure out (and I don't think it'll be hard)
is how to get the Axis module interfaced to the WTS701. It needs to
use SPI. You might be able to do it through the sync serial port or
bit bash off the parellel port. Beware that it's 3.3v logic although the
TTS chip claims to be 5V tolerant. I'd still put a level shifter in there.
>Subject: Sound with Etrax
>Date: Wed, 15 Oct 2003 13:38:18 +0200
>To be able to control devices connected to the devboard_82 by a telephone,
>will attach a GSM-modem and a DTMF-decoder so that the user may call the
>Axis-Board and give commands via pressing the phone-buttons.
>For this purpose, I want the Axis-board to provide a spoken "menu".
>My idea for this:
>- upload of sound-samples in PCM-Format to Devboard (8kHz sampling-rate,
>8bit/sample, in total not more than 60sec)
>- connecting a DAC to a sync serial port
>- generating the appropriate data-stream output on the sync serial port
>- feeding the mic-port of the modem with the analogue signal from the DAC
>Now there are several questions:
>1) Is there a better way? I think it should be possible to generate
>PWM-signals on the serial port and low-pass filter them to achieve an
>analogue audio signal. The sound should not be high-quality, just
>Another idea would be to use a text-to-speech module. Any experiences?
>2) The DAC needs at least 18bit/sample, and works in stereo mode (two
>channels). As the sync serial port only supports 16 or 24 bit/frame, it
>seems that I have to use 24 bit-mode.
>In this case, the clock had to be 8kHz*24*2=384kHz, which is not derivable
>from the 4.096 MHz clock nor from the 3.125 MHz clock. I think I do have to
>change the sample-rate or use an external clock with 3.072 MHz?
>3) For the I2S-bus Audio-Data-Stream the Frame-signal is half the time high
>and half the time low, for selecting right or left channel. The data-stream
>should be valid in each cycle. Is this possible? It seems that in normal
>operation mode the data-stream is only valid in one of the Frame-signal
>states (either high OR low). In this case, I would never be able to use
>4) Is there an audio-decompression-tool available, running on the Etrax, to
>use less memory for audio-samples? 60s PCM-data use about 500kB.
>5) I would like to have also 2 additional RS232-Ports. Is this possible, or
>do I have to forget about one RS232 if I connect the DAC?
>Well, many questions, but I would appreciate any hint!
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