After these steps, when someone presses either of the puppet’s hands or
presses its nose, it plays whatever you programmed in the sound synthesizer
for that particular switch.
Although the hand puppet we work with in this chapter might seem like a toy,
it’s not intended for small children. The wires and small electronic compo-
nents could be swallowed, and you don’t certainly want small kids playing
with batteries.
Scoping Out the Schematic .........................................................................
You have only one breadboard to put together for this project. You can see
the schematic for the board in Figure 7-2.
The following is a list of the schematic elements for our Murmuring Merlin.
IC1is a SpeakJet sound synthesizer model. You can connect this IC to
your computer and program it to generate electrical signals by using
software supplied by the manufacturer. These signals correspond to
words that form sentences, sounds that create music, or various cool
sound effects. The software allows you to program eight sounds; each
sound is controlled by one of the Pins 1–4 and 6–9 of the IC.
C1is a capacitor that filters noise from the +4.5V supply to IC2.
Switches S1, S2, and S3control the voltage on Pins 2, 4, and 7. The
switches are normally open,which means each pin is normally con-
nected to ground. When you push one of the switches, the voltage on
the corresponding pin raises to +4.5 volts. When you release the switch,
the voltage on the pin returns to ground. Because we programmed the
SpeakJet to trigger when the voltage on a pin changes from high (+4.5
volts) to low (ground), the sound which that pin controls is triggered
when you press and release the corresponding switch. We used three
switches to control three sounds because the puppet we used has three
handy spots where we could place switches. (If you’re lucky enough to
find an octopus puppet, you can have up to eight switches, controlling
up to eight sounds.)
IC2,a MAX232 driver/receiver chip, converts the signals from your com-
puter. These signals aren’t generated with the correct voltage for this
circuit, so signals have to be converted so that they can be used by the
SpeakJet chip. This chip also converts signals from the SpeakJet into sig-
nals that your computer can use.
Chapter 7: Murmuring Merlin .......................................................................................
