Focusing Sound With a Parabolic Microphone
Perusing the Parts List
Here comes our favorite part — shopping for parts! The upcoming Figures 6-3 and 6-4 show many of the parts used in this project. Here’s what you’ll need:
Electret microphone cartridge Trust us. We tried a lot of microphones to get this working just right (and save you the trouble). We finally decided on the Panasonic part #WM61A because of its very high sensitivity that allows it to pick up faint sounds. We found the WM61 at Digikey (www.digikey.com). 10 kohm potentiometer (R2) 10 ohm resistor (R3) 5.6 kohm resistor (R1) 0.1 microfarad ceramic capacitor (C1) 0.047 microfarad ceramic capacitor (C5) 10 microfarad electrolytic capacitors (C2, C3) 100 microfarad electrolytic capacitor (C4) LM386N-1 amplifier IC1 Of the many versions of the LM386 amplifier, we chose the LM386N-1 because it is designed to work with the supply voltage of 6 volts required by this circuit. Battery pack for 4 AA batteries Edmund Scientific’s (www.edsci.com) 24"-diameter parabolic reflector, part #3053876 SPST toggle switch, used as the on/off switch 830-pin breadboard Five 2-pin terminal blocks Knobs for the potentiometer Two phono jacks Two right-angle phone plugs We use right-angle plugs to avoid having a loop of wire coming out of the box. (You can also use something called a banana plug and jack.) Headphones We used a set of Philips HP170, but you can use any headphone you have available. Obviously, the better quality headphone you use, the better the sound quality. Headphone jack We used a 1⁄4" jack. If your headphone plug is a different size, use the appropriate size jack or get an adaptor.Enclosure to protect the circuit
We used a plastic box, RadioShack part #2701807.
An assortment of different lengths of prestripped, short 22 AWG wire PVC adaptor with 3⁄4" female slip fitting on one end and a 1" thread fitting on the other end PVC 90° joint with a 1" slip fitting on both ends (one male and one female) PVC adaptor 1" female slip fitting to a 1" female thread PVC 1" end cap with a 1" female slip fitting 5⁄16"-diameter wooden dowel Washer with a 1⁄4" inner diameter (ID) and 11⁄2" outer diameter (OD) 3⁄16" ID rubber 0-ring 1⁄4" thick rubber gasket material 1" diameter schedule 40 PVC pipe, 16" long 1" clamp Four 1⁄2" 8-32 panhead screws Four 8-32 nutsYou should be able to find the last 12 parts on this list at your local building supply or hardware store. Take this List with you: The photos should help you pick out the right parts, and everybody who sees you with it will realize just how smart you are.
