HOME
CARRIER OSCILLATOR VCC
C4
7 14
CD4069UB
U1A
0.1μF 1 2
34
R13
5.11kΩ
CD4069UB
U1B
AM MODULATOR
R11
10kΩ
VCC
R1
5kΩ
C8
0.1μF
C1
100pF
U2A
1
7 14
R10
10kΩ
CD4070
3
2
MODULATION OSCILLATOR
11
R12
5.11kΩ
CD4069UB
U1E U1F
10
13
CD4069UB
RED
WIRE
J3
9V BATTERY
CONNECTOR
R2
5kΩ
C2
0.1μF
BLACK
WIRE
OUTPUT AMPLIFIER
R6
100Ω
VCC
VCC
C3
0.O1μF
R5
6.19kΩ
Q1
2N3904
R3
1kΩ
R4
2kΩ
C5
0.1μF
J2
BLACK
J1
RED 1
1
C6
0.1μF
R7
51.1Ω
R8
100Ω
POWER SUPPLY
SW1
SPDT
VCC
D1
1N914
C7
10μF
D2
RED
R9
1kΩ
MATERIALS
All parts are available from Mouser Electronics
( mouser.com). For a complete list of part numbers,
see makezine.com/20/diyhome_wirefinder.
1N914 junction diode part reference D1
3mm LED, red D2
9V battery connector J3
2N3904 NPN transistor Q1
5kΩ potentiometers, single turn ( 2)
Mouser #652-3386H-1-502LF, R1–R2
SPDT push-button switch SW1
CD4069 hex inverter, CMOS Mouser #511-4069U, U1
CD4070 XOR quad exclusive-OR gate, CMOS
Mouser #511-4070, U2
Capacitors:
0.1μF, 10%, 100V ( 5) C2, C4–C6, C8
100pF, 50V, 5% C1
0.01μF, 50V, 10% C3
10μF electrolytic, 20V, 10% C7
Sockets, 14-pin DIP ( 2)
Banana jacks, panel mount ( 2) red J1 and black J2
Resistors, ¼W, 1%:
1kΩ ( 2) R3, R9
10kΩ ( 2) R10, R11
2kΩ R4
6.19kΩ R5
100Ω ( 2) R6, R8
51.1Ω R7
5.11kΩ ( 2) R12, R13
Project enclosure and protoboard to fit
142 Make: Volume 20
reach the isolated segment. So when you move past
the break, the signal level drops off rapidly. Using
the WireFinder, we were able to locate the break in
our wire quite accurately: the place we started
digging was only 2 feet from the break.
This technique works for finding both simple
wires — like our invisible fence — and buried coaxial
cables as well.
To keep things simple and cheap, we chose a
regular AM radio as the receiver. Then we designed
our transmitter to generate a signal of the right
frequency and modulation type so that an AM radio
can pick it up. Fortunately, the AM radio band is
very low-frequency, which makes construction and
wiring very simple. The total cost of the transmitter
(Figure A) is about $35.
Construction
Build the transmitter circuit as shown in the
schematic diagram (above). Standard wiring and
construction techniques can be used. Because
AM radio operates at a relatively low frequency,
high-frequency construction techniques, such as
controlled-impedance lines or coaxial cables, are
not required. Figure B shows how we arranged the
components on the protoboard.
