Chemelec TR detector

[Jafar]

Hi Carl,
I’ve built the T/R Locator metal detector designed by Gary Lecomte (CHEMELEC) based on its schematic and circuit diagram. The transmitter is currently operating at a frequency of 2.048 kHz.

I’d like to start a conversation about it so I can ask a few questions:

The search coils are 15 mH — should they be built perpendicular to each other?
What is the best type of search coil for this device?
Also, when I connect the transmitter and receiver wires, the device goes into detection mode due to their proximity.


I’ll explain more with a photo.

[Carl-NC]

Please use a new thread for a new conversation.
I don't know anything about this design. Is there a schematic? An old discussion thread?

[Jafar]

Please use a new thread for a new conversation.
I don't know anything about this design. Is there a schematic? An old discussion thread?

"Yes, the name of the device is T/R Locator, designed by Gary Lecomte, and I wanted to implement it."

[GeoMax]

Hi Jafar,

FYI... the T/R locator was not designed by Gary Lecomte. The original design was made by Sevzirfo. Check-out the forum here 2 boxxxx - Geotech Forums. There are 49 Pages of information about the T/R Locator.

Here is the link to the original website from Sevzirfo. TRlocator. The website is in russian. There are also pictures of the T/R Locator.

[Jafar]

Hi Jafar,

FYI... the T/R locator was not designed by Gary Lecomte. The original design was made by Sevzirfo. Check-out the forum here 2 boxxxx - Geotech Forums. There are 49 Pages of information about the T/R Locator.

Here is the link to the original website from Sevzirfo. TRlocator. The website is in russian. There are also pictures of the T/R Locator.

Thank you for your guidance. I will study it today, and if my problem isn't resolved, I will ask you. I will also be grateful to anyone who helps me.

[Jafar]

Hi Jafar,

FYI... the T/R locator was not designed by Gary Lecomte. The original design was made by Sevzirfo. Check-out the forum here 2 boxxxx - Geotech Forums. There are 49 Pages of information about the T/R Locator.

Here is the link to the original website from Sevzirfo. TRlocator. The website is in russian. There are also pictures of the T/R Locator.

Hello friends,

I have a 2.048 kHz frequency at the output of the divider IC4A, pin 14 (Q3), and I also see the same 2.048 kHz frequency at the TX output. However, I’m not sure what the expected peak-to-peak voltage should be.

My transmitter coil has an inductance of approximately 15 mH, and I’m using a 200 nF capacitor. I believe that with this capacitor value, the circuit is not in resonance at the 2.048KHz frequency, which means it may not be transferring maximum current through the coil to generate a stronger field. Why do you think the designer didn’t optimize this?

My second issue is with the receiver.
No matter how I adjust the null (i.e., when the transmitter and receiver are positioned perpendicular to each other to minimize interference), the receiver still detects a peak-to-peak voltage of 2.78V. When I move it out of the null position, the voltage increases slightly to 3V.

Your help and guidance are truly valuable to me—please don’t hesitate to share your insights.

Also, my voltage divider is giving me:
+6V
-5.98V
Do you think this is acceptable, or could it be causing issues?

[GeoMax]

Hi Jafar,

is the coil inductance of 15mH correct? This is the value that Gary used in his tests. Have you calculated the original coil specs by Sevzirfo?


This is from Sevzirfo's website:

Simple Depth Drill - T/R Locator ver1.0
This metal detector is designed to search for LARGE objects made of non-ferrous and ferrous metals. The scheme does not provide for compensation for the influence of the earth, so you can search only on poorly mineralized soils. Sensitivity to small objects such as cartridge cases, nails and small fragments is sharply reduced. It is possible to search for voids and inhomogeneities in the soil by the difference in soil conductivity.

Maximum detection depth obtained in practice:
Sheet of roofing iron 50x150cm - 3m (by air)
Passenger car............................... - 4m (air)

The detector operates in dynamic mode and does not require a manual zero setting. The operating frequency is 2 kHz. The voltage amplitude across the transmission coil is 120 volts. Coils with a diameter of 38 cm, 150 turns of copper wire in enamel insulation with a cross-section of 0.4 mm. Both coils are shielded with foil, leaving a small area free from the foil 0.5-1 cm (to prevent the formation of a short-circuited coil).

[Jafar]

Please use a new thread for a new conversation.
I don't know anything about this design. Is there a schematic? An old discussion thread?

Hi Carl, can you join our conversation and help?

[Jafar]

Hi Jafar,

FYI... the T/R locator was not designed by Gary Lecomte. The original design was made by Sevzirfo. Check-out the forum here 2 boxxxx - Geotech Forums. There are 49 Pages of information about the T/R Locator.

Here is the link to the original website from Sevzirfo. TRlocator. The website is in russian. There are also pictures of the T/R Locator.

"Today I read through the entire 2 boxxxx conversation, and none of their comments were useful. Nobody had done any troubleshooting either. Nevertheless, I’d appreciate it if someone could help fix this problem."

[nejdet]

What is the resistance of the two coils, give the size, show pictures of the coils. These small inductors are not good if you use them! The coils are much larger! The voltage divider is good!

[Carl-NC]

I have a 2.048 kHz frequency at the output of the divider IC4A, pin 14 (Q3), and I also see the same 2.048 kHz frequency at the TX output. However, I’m not sure what the expected peak-to-peak voltage should be.

I don't know, but I would not expect 120v. Maybe 20-40 vpp.

My transmitter coil has an inductance of approximately 15 mH, and I’m using a 200 nF capacitor. I believe that with this capacitor value, the circuit is not in resonance at the 2.048KHz frequency, which means it may not be transferring maximum current through the coil to generate a stronger field. Why do you think the designer didn’t optimize this?

The TX is not intended to operate in resonance, it is intentionally operated off-resonance to create an AM waveform. If the drive frequency is 2.048kHz and the resonance frequency is 2.905kHz then the AM envelope will be 857 Hz and this will be demodulated by the diode envelope detector (D3/D4) and becomes the audio frequency.

My second issue is with the receiver.
No matter how I adjust the null (i.e., when the transmitter and receiver are positioned perpendicular to each other to minimize interference), the receiver still detects a peak-to-peak voltage of 2.78V. When I move it out of the null position, the voltage increases slightly to 3V.

Do you have any metal around? Nulling has to be done in a very metal-free area. If you move the TX coil farther away does the RX amplitude drop towards zero?

Also, my voltage divider is giving me:
+6V
-5.98V

They are fine.

[pito]

Add a 10 nf capacitor, in tx circuit

[Jafar]

The resistance of one of the coils is 28.5 ohms and the other is 29.3 ohms.
I did not use an inductor; they are two parallel capacitors, which in the new revision I connected to the ends of the coils.

[Jafar]

I don't know, but I would not expect 120v. Maybe 20-40 vpp.

.

“The two images with higher voltage are related to TX, and the single image with lower voltage is related to RX. I used 28AWG wire for the winding.”

[Jafar]

“Carl, I changed resistors R16 and R17 from 1.2 kΩ to 100 Ω in order to increase the TX voltage, but it didn’t make any difference.”