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Minimalist Induction-Balance Metal Detector

A low-cost treasure hunter

Minimalist Induction-Balance Metal Detector
This design is arguably the simplest IB (induction balance) metal detector that could be built from off the shelf components. The IB method of metal detection has a good depth of penetration and discriminates well between ferrous and non-ferrous metals.Metal detectors are available commercially but their price tag is often prohibitive to youngsters and those just starting out with the treasure hunting hobby. This article proposes a metal detector that is fun to build at a very low investment. Carefully built and aligned, it will clearly pick up a tiny 15 mm dia. brass coin at 70 mm in air, or a 25 mm coin at 120 mm. It will not fail to pick these up vaguely at up to one quarter greater distance. The ability to locate coins buried in the soil are, of course, dependent on soil conditions, dry sand being the most favourable, and clay, the worst, ‘medium’ between the treasure and the search head.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info, Update
Unfortunately a few mistakes have been made in the numbering of three ICs on PCB 020290-1. This affects the component overlay of the board (Figure 2).Position IC1 on the printed circuit board should be IC4 (LM317).Position IC2 on the printed circuit board should be IC1 (7555).Position IC4 on the printed circuit board should be IC2 (7555).
Resistors:
R1 = 2k?7
R2 = 470?
R3,R5,R6 = 100k?
R4 = 4k?7
R7 = 1k?
R8,R9 = 100?
P1 = 50k? potentiometer, linear
P2 = 2k?5 potentiometer, linear
Capacitors:
C1 = 100µF 25V radial
C2 = 47µF 10V radial
C3 = 10nF
C4, C6 = 10µF 10V radial
C7-C11 = 100nF
Semiconductors:
D1 = 1N4001
IC1,IC2 = 555C, TLC555, 7555 (CMOS)
IC3 = TL071 CP, TL081 CP
IC4 = (LM)317T (in TO220 case )
Miscellaneous:
K1, K2 = 3-way PCB terminal block, lead pitch 5mm
BZ1 = passive (ac) piezo buzzer
PC1,PC2 = solder pins
12V battery or battery block (8 AA penlight cells)
36-30 SWG (0.2-0.3mm dia.) enamelled copper wire, 2 x 50m
Enclosure: Bimbox 5004-14 or Hammond 1590B (109x58x25mm)
5m symmetrical screened microphone cable (two wires with common screening)
PCB, order code 020290-1
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