Practical Arduino Cool Projects for Open Source Hardware- P17: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | C H A P T E R 9 Speech Synthesizer Synthesized speech was for a long time the Holy Grail of computing. 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 1980s and early 1990s was the famous General Instrument SPO256A-AL2 Allophone Speech Processor. It was used in toys external speech synthesizer peripherals for desktop computers 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. Nowadays of course it is almost always done entirely with software in the main CPU using only a tiny fraction of the available processing power. As a result the SPO256 became unnecessary dropped out of production and became a footnote in the history of technology. This leaves Arduino developers in a quandary because in terms of processing power the ATMega chips put us back into the realm of 1980s desktop performance 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. And 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 .
