S1is a normally open (NO) pushbutton switch that when depressed,
connects Pin 27 of IC1 to ground. This is how you record sounds to
IC1 through the microphone. Recording stops when you release the
S1 pushbutton.
R3is a resistor that connects the microphone to +V, supplying the 4.5
volts that the microphone needs to function.C3is a capacitor that removes the DC voltage from the AC signal that’s
flowing from the microphone to Pin 17 of IC1.
S2 is the on/off switch between the negative terminal of the battery pack
and the ground bus of the circuit board.R1and C1filter out that pesky electrical noise.
R2and C2connect the automatic gain control circuit inside IC1 to
ground. The values of R2 and C2 determine how fast the automatic gain
control responds to changes in volume when you’re recording a message.Building alert: Construction issues..................................................
Plastic pumpkins present unique building challenges, as everybody (who
bothers to think about it) knows. The curved shape of the pumpkin makes it
difficult to stick your hands inside to attach wires to terminal blocks. There-
fore, we attached the wires from most components — like switches and
speakers — to terminal blocks on the breadboard before placing them in
the pumpkin or attaching the components to the side of the pumpkin.
Wrap each lead of the IR detector and microphone in electrical tape after
they have cooled from soldering to make sure that the bare soldered leads
don’t touch each other. Leads co-mingling in this fashion can cause minor
electrical disasters.
We used a utility knife and small wire cutters to cut the holes in the plastic
pumpkins. Make sure that the plastic is not too brittle, and be sure to wear
safety goggles to protect your eyes against flying pumpkin pieces and leather
work gloves to protect your hands.
We placed some foam in the bottom of the pumpkins on which to rest the
breadboards. The type of foam used for flower arrangements is easy to cut,
but it’s so fine that particles go everywhere. The foam that you find in pack-
ing boxes will also shred, but the pieces are bigger and a little easier to clean
up. In either case, plan to spend some time cleaning up your cutting surface
afterward and don’t cut on your electronics bench — you don’t want those
foam pieces to get into the electronics bits and pieces.
Chapter 9: Scary Pumpkins 193