The deep metal detector DBP 2010

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There are several errors in the schematic of The deep metal detector DBP 2010, which may have been introduced intentionally or unintentionally.

DBP 2010 Main PCB Parts List

Resistors (1% Metal Film)

Reference	Value
R1	22 kΩ
R2	684 kΩ
R3	317 kΩ
R4	120 kΩ
R5, R20	5.6 kΩ
R6, R10, R17, R28	100 kΩ
R7, R9, R31, R33	10 kΩ
R8, R38	46.4 kΩ (see note below)
R11	22 kΩ
R12	40.7 kΩ
R13, R15, R21	56 kΩ
R14	8.2 kΩ
R16	12 kΩ
R18, R29	1.5 kΩ
R19	4.7 kΩ
R22, R30	330 Ω
R23	6.8 kΩ
R24	22 kΩ
R25	2.2 kΩ
R26, R27	825 Ω
R32	1 kΩ
R34	680 Ω
R35	47 Ω
R36, R38	1 Ω (see note below)
R37	39 Ω
R39, R40	100 Ω
R41	2.2 MΩ
R42	1.5 MΩ
RV	820 Ω

Potentiometers

Reference	Value
P1, P2, P3	25 kΩ Trimmer
P4, P5, P6	25 kΩ Potentiometer
P7, P8	250 kΩ Potentiometer

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Capacitors

Reference	Value	Type
C1	10 µF	Electrolytic
C2	2.2 nF	Ceramic
C3, C11	100 nF	MKT Polyester
C4	100 pF	Ceramic
C5	12 nF	Styroflex
C6	1 nF	Ceramic
C7	220 nF	MKT Polyester
C8	10 pF	Styroflex
C9, C13, C15	100 µF	Electrolytic
C10	12 nF	Ceramic
C12, C14	220 µF	Electrolytic
C16	4700 µF	Electrolytic

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Semiconductors

Diodes

Reference	Part
D1–D11, D13–D17	1N4481
D18	1N4001
D12	8.2 V Zener Diode, 0.5 W

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Transistors

Reference	Part
T1, T2	2N4124
T3, T4	2N4126
T5	MPSA14
T6	2N4403
T7	2N3773

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Integrated Circuits

Reference	Part
IC1	ICM7556IPD
IC2	CD4017BCN
IC3	LM741CN
IC4	LF357N
IC5	NE555CN (555CN)

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Other Components

Item	Specification
Search Coil	See coil specifications
Power Switch	1 × ON/OFF
Push Buttons	2 × Momentary
Meter	100 µA Analog Meter
Fuse Holder	For miniature fuse
Fuse	500 mA
Headphones	High-impedance
Speaker	8 Ω, 1 W
Battery	12 V, 2 Ah
Header Connector	3-pin
Header Connector	10-pin

Main PCB (without the module board)

Errors correction:

• Transistor T4 (2N4126) – the collector and emitter are reversed.
• Transistor T5 (MPSA14) – the collector and emitter are reversed.
• R38 = 1 Ω should be replaced with 10–32 Ω.

Module Board schematic

Module PCB (without the main board)

Errors correction:

• Transistor T3 – the collector and emitter are reversed.
• R34 = 680 Ω in the original design (its exact value should be determined experimentally depending on the gain of T7 = 2N3773), so that the pulse signal at the collector reaches 130 V peak-to-peak when the “Leistung” (Power) control is set to 10.

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Filters and Waveforms

Filter 1 should adjust the frequency from 290 Hz to 380 Hz:

• Position 0 = 290 Hz
• Position 10 = 380 Hz

Filter 2 should adjust the frequency from 380 Hz to 560 Hz:

• Position 0 = 380 Hz
• Position 10 = 560 Hz

Measured frequencies on the IC pins with the detector switched on and ready for operation:

IC1A

• Pins 2 and 6 = 60 Hz
• Pin 3 = 170 Hz
• Pin 1 = 2.2 kHz
• Pin 5 = 90 Hz

IC2

• Pins 8 and 12 = 280 Hz
• Pin 11 = 210 Hz
• Pin 9 = 650 Hz

T7 (2N3773)

• Collector frequency = 90 Hz
• Collector voltage = 130 V peak-to-peak

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Figure 3.43 shows the received signal measured at pin 6 of IC4 (LF357) when both filters are set to position 10.

• Signal width: 580 µs

The received signal at pin 6 of IC4 becomes approximately 170 µs when a metal object is close to the search coil.

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Circuit Operation Description

The transmitter signal is amplified at a switching frequency of 90 Hz by transistor 2N3773 (a replacement for 2SD551) to approximately 130 V peak-to-peak. It is then transmitted into the air through the search coil.

Proper damping of the search coil is achieved by R34 = 680 Ω, connected at the input of the coil, that is, at the collector of T7.

The switching frequency is generated by the first half of the dual timer IC1 (7556) and then doubled. It is used to set and reset IC2 (CD4017), which operates as a frequency divider and restores the operating frequency. Through transistor T5 (MPSA14) and 2N3773, it controls the transmission energy delivered to the search coil.

The second half of the dual timer IC1A (7556), together with operational amplifier IC3 (741) and the additional module board containing:

• IC6 = CA3140
• IC7 = IL709
• IC9 = CA3140
• CD4066

as well as five 2N4124 transistors, forms a timing control circuit with a built-in sample-and-hold function that measures and stores a reference value.

This section electronically compensates for the ground effect by measuring the ground’s capacitive characteristics and storing the reference value. The stored value is continuously compared with the received signal. This provides compensation for varying soil composition (minerals and ores) while allowing metallic objects to be detected independently of ground mineralization.

The detector operates by transmitting a pulse and then, after the timing sequence described above, switching to receive mode where it detects the signal reflected from metallic objects.

The received signal is applied to the input of IC4 (LF357). Thanks to the complex timing controller, the received signal is processed through a movable time window implemented by the LF357, allowing unwanted signals to be filtered out selectively.

The measurement window can be extended by using the frequency divider IC2 (CD4017).

The audio tone is generated by the LF357, together with IC5 (NE555) and transistor T3 (2N4126). The audio frequency is approximately 1.5 kHz.

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Search Coil Specifications

Table 1 – Empirical Detection Range Results

Standard Search Coils

Object	Material	Dimensions	DBP 2010 230 mm Coil	DBP 2010 430 mm Coil	VLF 770 230 mm Coil
Coin	Silver 800	40 × 3 mm	32 cm	39 cm	36 cm
Wedding ring	Gold 750	Ø 23 mm	18 cm	15 cm	29 cm
Steel plate	St 52	100 × 100 mm	68 cm	87 cm	60 cm
Bullet	Copper	Ø 20 mm	45 cm	61 cm	48 cm
Hand grenade	Cast steel	Ø 50 mm	61 cm	75 cm	51 cm
Jerry can	St 52	280 × 180 mm	118 cm	145 cm	93 cm
Stamped part	Copper	12 × 1.5 mm	21 cm	18 cm	24 cm
Coin	Alloy	1 Deutsche Mark	20 cm	16 cm	25 cm
Jerry can	St 52	300 × 500 mm	143 cm	185 cm	104 cm

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With Large Loop Coil and DBP 2010

Loop coil size: 1000 × 1000 mm

Object	Material	Dimensions	Detection Range
Hand grenade	Cast steel	Ø 50 mm	105 cm
Beverage can (Cola can)	Tin-plated steel	Ø 65 mm	110 cm
Steel plate	St 52	100 × 100 mm	115 cm
Steel plate	St 52	200 × 200 mm	172 cm
Jerry can	St 52	280 × 180 mm	225 cm
Steel plate	St 52	500 × 500 mm	265 cm

Search Coil Ø230 mm

• Diameter: 230 mm
• 43 turns
• Wire: 0.5 mm enamelled copper wire (CuL)
• Inductance: 858 µH

Search Coil Ø450 mm

• Diameter: 450 mm
• 23 turns
• Wire: 0.5 mm enamelled copper wire (CuL)

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I hope this explanation has simplified, at least to some extent, how the filters operate and what is important to adjust in order for the detector to function properly.

The remaining information and detailed instructions can be found in the published book.

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