TREASURE
FINDER
METAL DETECTOR KIT
Ramsey Electronics Model No. TF-1
Ahoy mates ! Go searching for buried treasure in your own
backyard, nearby park, or on the beach. This professional
quality unit can find metal at a depth of six inches!
Talk about your ideal project, this one will literally “pay for itself”
finding hidden treasures!
• Sensitive...you bet ! Uses a Faraday shielded search coil just like
the pro’s !
• Runs on 9-12 volts DC ; internal power regulation for “rock solid”
performance.
• E-Z grip handle for comfortable use.
• “Breaks down” small enough to fit in a suitcase or backpack ...
ideal for trips or hikes.
• Utilizes the Signetics® NE 602 mixer / oscillator integrated circuit
for worry free operation.
• Convenient earphone output for earphone / headset operation....
volume limited to protect your eardrums!
• Complete and informative instructions guide you to a kit that works
the first time, every time - enhances resale value, too !
TF1 • 1
RAMSEY TRANSMITTER KITS
• The “Cube” MicroStation Transmitter
• FM-25 synthesized FM Transmitter
• FM-100 Stereo FM Transmitter
• AM-1 AM Transmitter
RAMSEY RECEIVER KITS
• FR-1 FM Broadcast Receiver
• AR-1 Aircraft Band Receiver
• SR-1 Shortwave Receiver
• AA-7 Active Antenna
• SC-1 Shortwave Converter
RAMSEY HOBBY KITS
• SG-7 Personal Speed Radar
• SS-70 Speech Scrambler
• MX Series High Performance Mixer
• MD-3 Microwave Motion Detector
• PH-10 Peak hold Meter
• LC-1 Inductance-Capacitance Meter
RAMSEY AMATEUR RADIO KITS
• FX Series VHF and UHF Transceivers
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CW-70 CW Keyer
• PA Series VHF and UHF Power Amplifiers
• Packet Computer Interfaces
• QRP Power Amplifiers
RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN.
New kits are always under development. Write or call for our free Ramsey
catalog.
TF-1 TREASURE FINDER METAL DETECTOR KIT INSTRUCTION MANUAL
Ramsey Electronics publication No. MTF-1 Revision 1.0
COPYRIGHT
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.
1998 by Ramsey Electronics, Inc. 793 Canning Parkway, Victor, New York
First printing: May,1998
TF1 • 2
Ramsey Publication No. MTF-1
Price $5.00
INSTRUCTION MANUAL FOR
TREASURE FINDER
METAL DETECTOR
TABLE OF CONTENTS
Introduction to the TF-1 ................. 4
TF-1 Circuit Description ................ 4
TF-1 Assembly Steps ..................... 8
Schematic diagram ...................... 12
Component Layout ....................... 13
Initial Testing ................................ 21
Troubleshooting ........................... 22
Ramsey warranty ......................... 23
RAMSEY ELECTRONICS, INC.
793 Canning Parkway
Victor, New York 14564
Phone (716) 924-4560
Fax (716) 924-4555
TF1 • 3
INTRODUCTION
Searching for buried treasure has been a childhood dream for most of us. If
we could only “see” what's under a few inches of soil who knows what
fascinating delights await us! Could it be antique coins, missing jewelry, or
that coffee can that Gramps buried his fortune in?
But one look at the metal detectors on the market today and our dreams are
dashed! Even the “inexpensive” versions of a metal detector unit may cost
upwards of one hundred dollars; with the “professional” units selling for five
to ten times more.
Enter the Ramsey TF-1 treasure finder metal detector unit. Using today's
superior integrated circuit technology and a little physics know-how, we’ve
come up with a great circuit that performs admirably with a minimum of
tuning. With great sensitivity, selectivity, and ease of tuning we offer the
easiest and most reliable way to start seeking buried treasure of your own!
TF-1 CIRCUIT DESCRIPTION
The following paragraphs describe some of the circuit theory for our metal
detector kit. Have a look at the block diagram (pg. 5) and schematic diagram
(pg. 12) and follow along.
We’ll start by describing the entire circuit operation with a simple block
diagram. First of all let's get this search coil term figured out. What magic
properties happen when you wind a few turns of wire? Well, remember when
you hooked up that dry cell with the nail and the coil of wire? It did pick up a
few paper clips, now didn’t it. This is due to the fact that a current through the
wire creates a magnetic field around the core. By the same token, if we were
to “cut” through this magnetic field with a wire, we would induce a voltage on
the wire. This is the principle that the power company generators use to
produce electricity, as well.
When that same coil of
wire is used in an
S
N
alternating current circuit,
the nature of the search
coil begins to show itself.
As the electric current
races back and forth
through the wire (that's
why they call it
Figure 1 : Magnetism
from a coil of wire
+
“alternating”), that magnetic poles are also oscillating
back and forth.
TF1 • 4
So this oscillation is generating a “pulsating” magnetic wave. This magnetic
wave expands and contracts around the coil. When this magnetic “wave”
comes in contact with a metal object it induces a small voltage at either end
of the metallic “target”. With this induced voltage across the target object, a
small current begins to flow causing a “counter” magnetic field to be
generated by the target metal. This opposing field interacts with the search
coil, generating a counter reactance when metal is encountered. Since our
search coil is designed to work with only the magnetic field generated by the
coil, we can actually shield out the electric field interference by enclosing the
coil in a “Faraday” shielding arrangement. Seems a little crazy to enclose
most of our coil in a tube of copper, but it actually improves the performance
of the search coil!
So how do we transpose this change in reactance to a changing tone? We
use our coil in an oscillating circuit whose frequency is determined by the
inductance of the coil. This high frequency oscillation is much too high for our
senses to discern, however, so we need a way to make this changing
inductance usable. This is accomplished by “mixing” the signal with another
(local) oscillating signal. The mixer, simply put, combines the two input
Treasure Finder Metal Detector Block Diagram
Search Coil
Inductance
Tuned
Oscillator
Mixer
Tunable
Local
Oscilla tor
Amplifier
Speaker
frequencies and produces a sum (the inductance tuned oscillator + the
reference oscillator, and the difference (the inductance tuned oscillator - the
reference oscillator). This “mixed” (difference) frequency falls in the range of
our hearing, and the change in the pitch of the tone is proof that the coil is in
magnetic contact with some metal object.The frequency that we have
chosen for the oscillator provides for an optimal mixing frequency for the
mixer part of our circuit.
Now have a look at the schematic for the unit and follow along. The power
source for the treasure finder kit needs to be regulated to provide for drift
free operation of the two oscillator circuits that are contained in the kit. Diode
TF1 • 5
D3 is a zener type diode which accomplishes our regulation task. The power
indicator LED provides a visual display when the circuit is energized.
The local oscillator section of the circuit consists of U1 and its associated
components. This 8 pin chip contains a complete oscillator and mixer circuit.
This amazing little chip takes the place of several functional “blocks” critical
to our metal detector design. Since we will want to be able to slightly adjust
our local oscillator input, we have provided a “varactor” diode tuning circuit in
order to enable us to to change the frequency of our reference. We have
used this particular IC for a few years now for a variety of applications and
are still amazed at how it lends itself to more and more designs.
The oscillator comprised of transistor Q1 and it associated components
(including the search coil) generates our probing magnetic field. Notice that
the search coil is isolated from the rest of the circuit via a length of RG174
mini coaxial cable to provide for more stable measurements.
Components R6 and C10 make up our low pass filter that removes the
unwanted mixer output (the sum of the LO and search coil oscillators) The
difference between the two oscillators is amplified by U2, an audio amplifier
integrated circuit. This IC can provide plenty of power to drive the small
speaker, so we also limited the power for use with the optional earphone by
adding a resistor (R10) in series with the headphone output.
TF-1 COMPONENTS LIST
Sort and “check off” the components in the boxes provided. It’s also helpful
to sort the parts into separate containers (egg cartons do nicely) to avoid
confusion while assembling the kit.
RESISTORS AND POTENTIOMETERS
1 2 ohm (red-black-gold) [R9]
3 120 ohm (brown-red-brown) [R2,10,13]
2 270 ohm (red-violet-brown) [R4,8]
2 1K ohm (brown-black-red) [R1,6]
2 10K ohm (brown-black-orange) [R3,5]
1 100K ohm (brown-black-yellow) [R12]
2 PC mount 10K ohm trimmer potentiometer (10K) [R7,11]
CAPACITORS AND INDUCTORS
❒ 1 470 pF disc capacitor (labeled 470 or 471) [C19]
❒ 2 .0015 uF disc capacitors (labeled .0015 or 1500K) [C5,17]
TF1 • 6
❒ 4 .01uF disc capacitors (labeled .01 or 103 or 10nF) [C6,10,16,13]
❒ 2 .01 uF Mylar capacitor (in a rectangular case [looks like a Chicklet]
labeled 103) [C7,18]
❒ 6 .1uF disc capacitors (labeled .1 or 104) [C2,3,8,11,14,15]
❒ 2 10 uF electrolytic capacitor (labeled 10uF) [C1,4]
❒ 2 220 uF electrolytic capacitors (labeled 220uF) [C9,12]
❒ 1 100 uH inductor (coil on form with hex tuning slug) [L2]
SEMICONDUCTORS AND INTEGRATED CIRCUITS
❒ 1 6.2 volt zener diode (small gray glass case with banded end) [D3]
❒ 1 Varactor diode (MVAM 108) [D2]
❒ 1 Jumbo LED (light emitting diode) [D1]
❒ 1 NPN Transistor (three leads marked 2N3904) [Q1]
❒ 1 NE602 mixer oscillator IC (8 pin DIP IC marked NE602) [U1]
❒ 1 LM 386 audio amplifier IC (8 pin DIP IC marked 386) [U2]
MISCELLANEOUS COMPONENTS
❒ 1 PC mount push-button switch [S1]
❒ 1 PC mount mini jack [J1]
❒ 1 9 volt rectangular battery “snap” connector
❒ 1 9 volt battery clip
❒ 1 Miniature 8 ohm speaker [SP1]
❒ 2 17” pieces of 1/2 “ PVC tubing, one having slots cut in the end; one
having three holes pre drilled
❒ 1 8 ” piece 1/2 “ PVC tubing
❒ 1 45 degree 1/2 “ PVC elbow
❒ 1 1/2 ” PVC endcap
❒ 1 1/2 ‘ PVC coupling
❒ 1 Foam grip handle
❒ 4 ’ RG-174 mini coaxial cable
❒ 35 ’ 24 AWG enameled magnet wire
❒ 18 ” 3/8 “ Diameter copper tubing
❒ 1 “Clamshell” abs plastic case with pre-punched panel set
❒ 1 Panel sticker set
❒ 2 #4-40 X 1 “ cover mounting screws
❒ 4 #4 x 3/8” self tapping screws
❒ 2 #6 type B self tapping screws
RAMSEY LEARN-AS-YOU-BUILD KIT ASSEMBLY
There are numerous solder connections on the TF-1 printed circuit board.
Therefore, PLEASE take us seriously when we say that good soldering is
essential to the proper operation of your metal detector!
TF1 • 7
Loading...