Mike's Speech Synthesizer (Part II)

       My wife wanted to get me something for my birthday that I REALLY wanted, and the thought of getting an electronic component would make most folks scream out "BORING!", but to me it was the perfect gift that would give me hours of enjoyment, and here it is nearly a year later and I am still having fun with a $25 component. I say money well spent. Thank you SparkFun!

     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.

Speakjet IC

      At first glance the IC does not seem very intimidating. Voltage supply and ground are clearly labeled. So are the Rx and Status pins. The only pins that arouse any sort of curiosity are the E0-E7 and the M0/M1 pins. As it turns out E0-E7 are event inputs to trigger different functions on the IC and M0/M1 are mode selectors  used to select between default and demo modes.

Demo Mode Diagram

     Ahh, "Demo Mode". This is what I can use to get a cheap, quick fix to make sure everything is operating properly while still getting the delightful feeling associated with making an obnoxious set of sounds. Because after all that is really the main drive behind these sorts of endeavors.

     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.

Demo Mode

     I was able to get around this limitation by using a 1:1 1000 ohm  audio isolation transformer I had laying around. This had the added benefit of protecting any amplifier I might hook this circuit up to. The picture to the right illustrates the Speakjet wired up in Demo Mode with the output going to the transformer. Pay no attention to the orange capacitors on the board, they are used further down the road. The only other component worth mentioning is the 10uF capacitor used to filter the power supply a bit where the power enters the main board. Below is a small video I put together that illustrates the Speakjet executing its demonstration mode.

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.

Stay tuned.

Mike’s Speech Synthesizer (Part I)

NURD!

 As a kid growing up in the early to mid-eighties, it would seem almost unnatural to NOT be thoroughly entrenched in the technological infancy that was the home computer industry at the time. Or at least that is what I told myself for lack of having friends and being socially awkward at the time, as well as today.

   My first home computer was the Texas Instruments TI 99/4a. It was a cumbersome machine as far as expandability and peripherals were concerned but none the less I had hours and hours of fun manning its keyboard. I was delighted to program it, since the TRS-80 Model III's they had at school had neither color nor sound. Texas Instruments was beginning to feel the squeeze in the home computer market and needed to pedal more of its wares out the door so I believe they offered the machine with a free speech synthesizer, which is how I got mine.

    This technology blew me away in 1983. An actual computer that could talk at my command. I think I played with that thing every day for a year. I even rigged up a device in my bedroom that would move a joystick when a door was opened and would trigger the computer to greet you upon entry.  It was like I was living the future and I was merely eleven years old.

    For all the short comings that the TI 99/4a computer had, I still held it dear within my heart. And this carried through when I picked up a used one for ten dollars at a flea market, spent another twelve on a speech synthesizer from eBay, and paid another ten dollars to get a Terminal Emulator II and Extended BASIC cartridge. The planets were aligning once again in 2012 for me to rekindle my interest in speech synthesizers. 

 

       Once all the pieces had arrived in the mail it was time to put them all together in my garage and make the past once again come alive with artificial voice. Above is a small program I cobbled together using TI Extended BASIC. It is not much but it did reignite my love of speech synthesizers, and further motivated me to press on in my tinkering of such things. I actually felt a bit giddy when I heard that robotic voice that I had not heard in nearly thirty years.

 

"E" is for ERROR!

      Suffice it to say I was not done playing with the TI 99/4a and it's speech capabilities. I set everything up in the living room and then wrote a small text to speech program using the Terminal Emulator II cartridge and it's many speech algorithms. This gave us all a few hours of enjoyment. I think the kids got the biggest kick out of it. Here is a photo of the little one teaching the other little one how to spell words that are spoken. This would have worked out rather well if it were not for the limitations of having to negotiate which words the program could phonically speak out when spelled correctly. None the less both kids were on the machine for no less then two hours straight. I found that rather amazing that in this day and age a few kids could be so engrossed with a piece of technology over thirty years old. In fact they used it for so long it actually burned out the VDC (Video Display Controller). I still need to fix that.

    So at this point I was left with no machine to fulfill my need for speech synthesis. The TI 99/4a was out of commission, and I hadn't picked up the Speak And Math in six months. I was not sure what I was going to do. 

    Luckily, it was around this time that a friend of mine had seen the TI Speaketh video and had asked me if I had ever played with a Speakjet speech synthesizer. I had no idea what this was and inquired further. It would appear that this Speakjet chip was a fully functional speech synthesizer that worked a lot like the old Votrax SC-01 speech synthesizer, in that they formed words out of allophones and diphthongs and such. You simply passed serial data to it and it would read the data out of it's buffer first in, first out. No more needed to be said. I had to have one of these.