R3is a resistor that connects the microphone to the +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.The speakeris connected to Pins 14 and 15 of IC1. The speaker is used
to play messages that you recorded on IC1 when the sensor connects
Pin 24 to ground.
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 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 ...........................................................
Because the Couch Pet-ato is likely to sit in your living room and we know
that you like a neat-looking home, we placed all the works in a wooden box to
make it look tidy.We went strolling down the aisle of a local craft store to find our wooden box,
but you might also find one in an office supply store — designed to hold index
cards, for example. Just make sure that it’s big enough to hold the breadboard.Because the walls of this box are thicker than the plastic boxes often used
for electronic gadgets, the threads on switches might not be long enough to
secure them to the side of the box. If this happens to you, just drill the hole
so that it’s large enough to slip only the shaft of the switch through; then use
glue to secure the switch.The size of drill bit that you use to drill holes for the switches, speaker, and
microphone depends upon the diameter of the components you’re using. We
used a^1 ⁄ 2 " drill bit to drill the hole for the switches and a^3 ⁄ 8 " bit to drill a hole
for the microphone. For the speaker, we used a^5 ⁄ 32 " bit to drill the holes to
which we attached screws for the speaker flange, and then we used a coping
saw to cut the center hole for the speaker.Perusing the Parts List ................................................................................
Here’s your shopping list for building your Couch Pet-ato. This project
involves the following parts, several of which are shown in Figure 14-3:346 Part IV: Good Vibrations