Servo - November 2012

FIGURE 5.

FIGURE 6.

Switched power connections and amplifier input on the PCB are easily traced with a multimeter. I removed the bottom three-conductor audio input cable entirely, and added two mounting screws while I was in there. RoboVoice audio output from pin 26 goes through a 10 µf cap into TWO connections on the amplifier PCB since it originally had stereo input. Just connect both together. You'll get reduced audio output if you only use one. BoeBot's breadboard area is just 17 rows long and nearly filled up by the 14-pin-long RoboVoice chip. That leaves just three rows of holes remaining after the chip is inserted. How do you add an LM386 audio amplifier then? CHEAT!

First, I gently folded the unused pins underneath the chip so they didn't even plug into the breadboard (Figure 5). Second, lower pins 14 and 15 are not used and hang over the edge of the breadboard in the breeze. (Not pretty, but it works!)

Those two cheats let you fit both chips into the breadboard and free up enough rows to make all the required connections (Figure 6).

A 3.3V regulator is required to power the 512. I found that the minimum-parts LM386 circuit — a 20X amplifier — drove a 16 ohm speaker with sufficiently loud volume. This was coupled to the RoboVoice directly through a 10 µF cap — no pot was used. Just for fun, I mounted the speaker on a servo to move it; the coffee cup horn definitely makes the sound louder and directional. An alternative to using the LM386 would be to use a hamburger amplifier speaker with only the RoboVoice chip plugged into the breadboard.

BASIC Stamp 2: Three simple connections use jumper wires or 10K resistors from the breadboard area to the adjacent pin headers. Pin 7 will use SEROUT 7,84,["hello world",CR] for speech; CR is a carriage return.

Arduino Uno: No shield is required since the female headers make it easy to connect. Digital pins 12 and 13 are adjacent to a ground connection; the male end of a servo extention cable plugs directly into these three connections. You will open a software serial port and use Speak.println("hello world"); for speech. Note that println includes an automatic carriage return at the end.

PICAXE 20M2: To achieve 9600 baud, the 20M2 must be run at 8 or 16 MHz (default is 4 MHz); 16 MHz is recommended for robotics apps since the servo commands are calibrated only for 4 and 16 MHz. Nearly any I/O pins can be used, but note that C. 6 is input only.

Per the manual, set the serial output pin high briefly before sending true data. Pin 4 uses SEROUT 4,T9600_ 16,("hello world", 13) to invoke speech. That 13 is a carriage return.

A PICAXE makes an inexpensive terminal to experiment "live" with the 512 chip. A $4 PICAXE 20M2 can read a computer keyboard directly (no host computer) and sends the data to one of the 512 speaker/amp modules. There’s a video at www.youtube .com/watch?v=UhhDEhzF3PM if you’re interested.

With the addition of an LCD screen, you have the makings of a Speak & Spell type application. A video of the Arduino and BoeBot singing is at www.youtube.com/ watch?v=J5GMOAIQbJ4.