adjusting the value of the variable resistor when the coil is not near any
metal objects.
R5 is a resistor connected between the output of IC1 and ground. When
the output of IC1 is on, current flows through this resistor and provides
a positive voltage to the base of Q1.Q1is a 2N3904 transistor that you connect to the output of IC1. When
the output of IC1 is high, Q1 turns on and allows current to flow through
LED1.
LED1is the indicator light used to indicate that the device has detected
metal in the vicinity.R3is a resistor that limits the amount of current flowing through LED1,
which prevents it from burning out.
S1is the on/off switch.Building Alert: Construction Issues ...........................................................
You use PVC cement (a glue) to connect the PVC fittings that form the micro-
phone handle. You can get this glue at any building supply store.This glue creates a very strong joint. However, be sure to wear some form
of work gloves when using this glue because it melts plastic — and you defi-
nitely don’t want it on your hands. Also read the label for safety tips, such as
using the glue in a well-ventilated area and what to do if some comes in con-
tact with your skin.Perusing the Parts List ................................................................................
Even though this project doesn’t require many parts, you still have to go out
and buy or assemble them. Several of the parts are shown in Figure 12-3.
Here’s what you need:Two 1 kohm resistors (R1, R4)10 kohm potentiometer (R2)
330 ohm resistor (R3)284 Part IV: Good Vibrations