Pulse Induction Metal Detector M158.2

Description

Specifications
➔ Depth of detection of a coin, cm 20 – 25 cm
➔ The depth of detection of the coin, 100 – 150 cm
➔ Power supply, 9-14 B
➔ Current consumption 60 – 70 mA
➔ Pulsed current consumption, 1 – 2 A
➔ Overall dimensions of the board, 45 X 43 mm

*The current consumption depends on the volume setting of the
speaker. At maximum volume, it can reach up to 240mA.

Assembly and configuration of the metal detector

The device consists of two main nodes: transmitting and receiving. The transmitting node consists of
a pulse generator on the chip U1 (NE555) and a powerful key on the transistor Q2. The receiving
node is assembled on the chip U2, diodes D1, D2, on R8 and transistor Q3. The excitation signal
from pin 3 of U1 is transmitted periodically to the coil of the sensor, through Q1, Q2 in the form of
pulses with a duration of 125-150 μs and a frequency of 125-150 Hz. In conducting objects, damped
eddy currents are induced, which excite a damped electromagnetic field. Depending on the
conductive properties and size of the object, the signal changes its shape and duration, standing out
on the detector D1, D2, R8. Further, the signal, amplified by U2A, goes to the scheme of the
selection of the useful signal collected on RV1, RV2, C6, R12, R13, C7, U2B. Adjusting the
resistances of RV1, RV2, and is achieved by setting the maximum sensitivity of the device, a state in
which the signal no longer passes through the threshold in the output speaker. And if you now bring
the metal to the coil, the signal, having slightly increased, overcomes the trigger threshold and enters
the speaker, signaling that “there is a find.”

Assembling and setting up a metal detector

Settings are carried out away from industrial interference and large metal
objects. If at this moment any metal object is near the sensor coil, the device, it
is wrong. The power voltage is supplied to the contacts +VCC, 12V from the
battery (in cases with the power supply, there may be interference that will lead
to difficulty setting up the device). The search coil is connected to the contact
L1, and the SP1 contact is 8 Ohms/0.5 watts. When feeding, the device is
initiated by the device accompanied by blinking and characteristic sound. The
SW3 SW6 buttons set the minimum barrier value. The tuning resistor R3 is
rotated until the device begins to make sounds on its own, and then we turn the
R3 a little so that the device is silent. At each position of the tuning resistor, we
press the SW4 reset button and check the sensitivity. A good result by air can
be considered 22-25 cm for five cents. The setting of the metal detector can be
considered finished. To look for a metal, we install a barrier in which the
“instinct” of the device will be maximum with satisfactory stability. A well-tuned
device does not give false works at 3-4 barrier LEDs.

Making a search coil

For the manufacture of the search coil, you need a rigid non-metallic mandrel Ø 200-250 mm,
copper winding enamelled sew wire (Ø0.4 – 0.6 mm) 20 meters long, copper insulated stranded wire
2×1.5 mm2, 120-150 cm long fee. On the mandrel tightly wind 25 turns of magnet wire. Attach the
ends of the wire and solder them using soldering insulated wire with the board to the L1 contacts.

Assembly the setting of the metal detector

Connect the speaker 8 ohm 0.5 W to the Speaker1 contacts. Connect the coil to contacts
L1. Connect power to the contacts of Power1 9-14 Volts, while respecting the polarity! (Preferably
from the battery 12 V, 1.2 Ah).
Check the connection and fastening of the board again !!! Before switching on, make sure that there
are no metal and electrical components and devices in the coil area: such as a mobile phone, a
system unit, reinforcement rods in concrete or walls or floors, and metal profiles in the walls, or the
presence of metal inside the desktop, and in the area where the device is configured, etc.
After turning on the device, bring the variable resistor RV1 (fine tuning) engine to the middle
position. Rotate the trimmer resistor RV2 (coarse tuning) to find the position at which the clicks in
the dynamics will begin or disappear. Leave in the position of still audible clicks. Slightly unscrew
the resistor RV1 so that the clicks in the speaker subside. So leave. Maximum sensitivity is achieved
at the threshold of sound in the speaker. Sensitivity can be increased by increasing the number of
turns of the coil. With a mandrel diameter of 250 mm and a wire diameter of 0.5 mm, the number of
turns is 25. This quantity is optimal in terms of power consumption (battery life) and detection
depth.

After setting the maximum sensitivity, bring the metal object to the coil and observe the appearance
of a stable signal in the dynamics and its extinction as you move away from the coil. The device is
ready for operation.
In the process, you can always adjust the sensitivity of the variable resistor RV1 (or even RV2
(roughly)).
Pleasant searches and finds

Quick User Guide