untitled

Here’s a list of the schematic elements:

L1is a coil (also called an inductor) wired in parallel to capacitor C1; the

combination of this dynamic duo is a parallel LC(inductor/capacitor)

circuit. When a signal that oscillates at several kHz passes through this

circuit, the signal creates an electric field around the coil. When you

bring the coil near a metallic object, that electric field induces an oscil-

lating signal in the object. Turnabout is fair play, so when the oscillating

signal has been induced in the metallic object, the signal in the object

creates an electric field that induces current in the coil. This current

changes the oscillating signal running through the LC parallel circuit.

IC1is a TDA0161 proximity detector. This IC is designed to supply the

oscillating signal that’s sent through the LC parallel circuit. The IC also

responds to any changes in the signal: the IC has an output of 1 milliamp

(mA) or less if the coil is far from a metallic object and an output of 10

mA or higher if the coil is near a metallic object.

R1 is a resistor, and R2is a variable resistor. These resistors are used to

calibrate the circuit in IC1 to the LC circuit. You calibrate the circuit by

R1

1

5

6

4

7

(^32)
C 1
C 2
IC 1
L1

R2

Q1

R3

LED1

R4

R5

6V

S 1

Figure 12-2:
The
schematic
of the metal
detector.

Chapter 12: A Handy-Dandy Metal Detector 283