Simple test program to drive a SpeakJet chip with an Arduino
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Speech Synthesizer Simple

Copyright 2009 Jonathan Oxer
Copyright 2009 Hugh Blemings

| This project is featured in the book "Practical Arduino" by         |
| Jonathan Oxer and Hugh Blemings (Apress, 2009). More information    |
| about the book and this project is available at:                    |
|                                                                     |
|         |

Synthesized speech was for a long time the Holy Grail of computing,
and back in the 1980s when a 4MHz CPU made your computer the fastest
machine in the neighborhood it just wasn't practical for software to
create intelligible speech. In those days the only sensible way to
generate speech was to offload the task to dedicated hardware because
the CPU simply couldn't keep up. The most widely used speech chip
through the 80s and early 90s was the famous SPO256A-AL2, the allophone
speech processor. It was used in toys, in external speech synthesizer
peripherals for desktop computers, in industrial control systems, and
all sorts of other unexpected places. Then as CPU power continued to
increase rapidly speech synthesis was moved to being a software
function, and nowadays of course it is almost always done entirely in
software by the main CPU using only a tiny fraction of the available
processing power. As a result the SPO256 dropped out of production and
became a footnote in the history of technology.

Which leaves Arduino developers in a quandary, because in terms of
processing power the ATmega chips put us back into the realm of 80s
desktops again. An ATmega could possibly produce intelligible speech
directly but it would use every available CPU cycle to do it, and the
Arduino itself would be pretty much useless at doing anything else at
the same time. Not much good if you just want to add voice feedback to
an existing project. However, the demise of the SPO256 means you can't
just link one up to your Arduino and offload speech generation to it.

With old stock of the SPO256 drying up Magnevation decided to do
something about it, and designed their own speech chip that works on
the same principles as its predecessor but has a much smaller physical
package and offers a handy serial interface rather than a clunky
parallel interface. The result is the SpeakJet, an 18-pin DIP device
that can do everything the old SPO256 did plus more.

In this project we assemble a speech-synthesizer shield that combines a
SpeakJet chip with a simple audio amplifier to let you add speech output
to a new or existing Arduino project.

This version of the code is a minimal test program that lets you send
a sequence of allophones to the SpeakJet chip and have it speak out a