I have always been a little afraid of playing with IC's. They easily frustrate me when what I think should be simply a logical on or off becomes frantic and random. Although I had Digital Electronics in high school, the part that was covered that discussed filtering capacitors and bounce free switching somehow got erased from my Pink Floyd addled cheap Mexican weed baked brain. Now that I am older, more bitter, and less intense I found that these things are more easily focused upon to where I would not make the same mistakes I made in the past. This time I choose to read through the extensive documentation of the Speakjet before it arrived in the mail.
|Demo Mode Diagram|
As it appears there is not too much rocket science in wiring this IC up into Demo Mode. It looks like all the event triggers (E0-E7) are grounded, and both Mode Selects M0/M1 are pulled high along with the reset line which is an active low. The only part that had me scratching my head was the output going to a 120 ohm speaker. I did not currently have such a speaker on hand and my power supply would be providing 5 volts instead of 3. So any speaker I hooked up to the output had to pull no more than the rated 25ma at 5 volts. A little calculating with Ohm's law (R = E/I) gave me a rating of 200 ohms for the resistance needed to max out the output current of the IC.
Now that I was able to verify that the Speakjet was working properly it was time to read more of the excellent documentation provided for this IC and attempt to hook it directly up to my laptop.