Metal detector Tracker FM-1D3
The main objective in developing the circuit is to minimize the influence of the soil on the search process and increase the comfort of working with the device. This was achieved by the following design solutions:
1) Using a relaxation generator with a minimum oscillation amplitude , which showed sufficient efficiency on real soil.
2) Introduction of an intermediate signal amplifier .
3) Using a dynamic operating mode .
4) Refusal of LED indication in favor of a loud and clear sound .
The applied generator and dynamic operating mode allowed to minimize the influence of the soil on the search coil (by reducing the residual magnetization of the earth), cut off harmful interference.
The modified power supply circuit (the generator, amplifier and microcontroller are powered by 3V) allows to increase the service life from one Krona battery without deteriorating the performance of the device.
The modernization can be considered as the best option for a frequency metal detector for use as the main one during search (naturally, taking into account its real characteristics).
Sensitivity:
Coin D=25mm —– 15cm.
Small infantry shovel —– 40cm.
Technical solutions used in this upgrade:
Generator:
Assembled according to the resonant generator circuit, which operates at the natural frequency of the oscillatory circuit L1C1. The advantage of this solution is, first of all, frequency stability over a wide range of supply voltages and the possibility of moving the circuit capacitor directly to the search coil. Thus, it was possible to eliminate the influence of the sensor-circuit wire on the circuit frequency.
Signal amplifier:
This cascade allows you to simultaneously solve two problems – amplify a weak generator signal and bring it to a form optimal for subsequent processing by the microcontroller. Thus, weak sinusoidal oscillations are transformed into a semblance of “digital” ones, with a steep front and decline.
Microcontroller:
As in the original version of the circuit, the microcontroller takes on all the work of signal processing. Specific functional features may vary depending on the firmware:
1D3boost – a modified version of the original firmware. Dynamic mode is left. All adjustments are removed. Buttons are not used. Sound bug is fixed.
1D3boost+ – firmware with increased sensitivity. Recommended for “quiet” interference environment and “light” soil.
Voltage stabilizer:
Implemented on the integrated stabilizer LM317. The output voltage is about 3V. Filter capacitors increase the stability and quality of the power supply of the entire circuit.
Search sensor:
It is an inductor coil and a film capacitor connected in parallel. A two-wire shielded wire is soldered to them, the other end of which is soldered to the board. The coil is enclosed in a foil screen using a known technology. This screen is soldered to the wire screen, and that, in turn, directly to the negative terminal of the power source. If you are planning a collapsible design or you want to make yourself several sensors of different diameters / frequencies, you can connect the sensor through a connector. It must provide high-quality contact and durability.
Recommended sensor parameters:
Coil 100 turns of 0.5 (or so) wire on a mandrel with a diameter of 19 cm.
A capacitor with a capacity of 47 nF (type K73-17 or the most thermally stable) is soldered directly to the coil terminals.
Indication:
It is advisable to use only sound indication, since in real search conditions it is not possible to constantly look at the LED scale. In this regard, a sound amplifier has been added to the circuit, allowing to significantly increase the sound volume. The maximum possible volume depends on the type of speaker used and the battery supply voltage.
Setting up the device:
After the board is assembled and all the wires are in place, you can turn on the power of the device. In case of normal operation, a short beep will be heard from the speaker and the device will enter the operating mode. If a continuous sound is heard from the speaker, it means that the analog part of the circuit (generator, amplifier) is assembled incorrectly.
The most likely causes of malfunctions (in the absence of installation errors):
– Resistor R3 has too high a resistance for the coil you used.
The circuit is designed to work with a search circuit with a frequency of 10 kHz. If the frequency is below a certain threshold, the generator will “stall”. Try adding another capacitor of 10 nF to capacitor C1. If the device starts working, you can leave everything as is, or remove the additional capacitor and reduce the rating of R3. It should be remembered that R3 should be as LARGE as possible, at which the device still works.
– The speaker or piezo emitter used is faulty (or of the wrong type). In this case, a serviceable device will behave like a “dead” one. The speaker or piezoelectric emitter should be replaced if there is no sound but there is a sound signal on the 2nd leg of the microcontroller.
List of parts and replacements for the Tracker FM-1D3 metal detector
Resistors:
1k – 1 piece
1k5 – 1 piece
4k7 – 3 pieces
100k – 3 pieces
10k* – 1 piece
Capacitors:
22p – 2 pieces
10n – 1 piece
47n – 1 piece
100n – 3 pieces
Electrolytes:
470μF x 16V – 1pc
1000μF x 6.3V – 1pc
Transistors:
KT3102 (BC547) – 4 pcs
KT3107 (BC557) – 1 pc
Other:
ATtiny2313 – 1pc
LM317L – 1pc
Quartz 10MHz – 1pc
Small speaker – 1pc
Switches (toggle switches) – 3pcs (in the current firmware version, only the power switch is used)
Possible replacements:
100k resistors can be replaced with a similar value.
1k5 resistor can be either 1k4 or 1k6.
4k7 resistors in the generator can be replaced with a similar value (up to 10k. Both are the same).
100n capacitors can be installed with a higher value.
22p capacitors can be replaced with a similar value (no more than 30p).
Electrolytic capacitors can be replaced with similar values.
Transistors can be replaced with similar ones specified, observing the pinout. The printed circuit board is designed for the K-B-E pinout.
Download firmware, PCB files, fuses for MK
Original design and firmware: Andrey Shchedrin and Yuri Kolokolov. http://www.metdet.ru/FM.htm
Discussion of the Tracker FM-1D3 metal detector circuit on the forum . There you will also find new firmware and can ask questions to the author of the circuit.
ARCHIVE: Download from server
