Current Projects:
Pinball Project
CNC Router
PIC Computer
LED Sign 2003

Talking PIC

One night during the perpetual boredom that is U of I Summer Session II, Joel Jordan and Jason Gallicchio had a vision...a vision that would change the ACM lab in the Digital Computer Lab forever (or at least until someone gets annoyed and breaks it). The project--to develop a circuit that welcomes visitors to the lab with a simulated voice--will go down in history as being one of the few projects Joel and Jason ever completed.

This page has been created to explain the inner workings of this ground-breaking project. The circuit used employs a PIC16F84 microcontroller to control a (now obsolete) SP0256 speech synthesizer IC originally purchased from Radio Shack several years ago. Data for this IC can be found with an Internet search, since it has been used in many projects. The circuit is activated when the door is opened through a simple normally closed momentary switch in series with the power supply.

The speech synthesizer works by combining standard phoenetic syllables to form full words. The syllables are stored on the IC in internal ROM, and an external microcontroller specifies which syllables to play. To produce the output sound, the SP0256 generates a pulse-width modulated digital signal which can be low-pass filtered to obtain the desired speech.

Our circuit is a modification of the example circuit specified on the SP0256's data sheet, shown below.

I don't yet have a good copy of our final schematic, but it is nearly identical save the elimination of the power-on reset circuitry using the spare output pins of the PIC. I'll put it hear as soon as I can, as well as a simple explanation of the circuit.

After building the circuit on a solderless breadboard, we decided to fabricate our own printed circuit board for the final design. The final layout is shown below. The finished board is 4 by 3 inches, single-sided. We etched it using toner transfer sheets obtained from DynaArt.