Bipolar PI MD with GB and DD Coil

[pechkata]

Can you post a video ?

I don't think we'll see a video like this.

[AhmatAhmatov1959]

Yes, I tested this scheme with 8" 300uH 2 oHms mono coil with 25 turns 0.14/1mm Teflon wire, 2 layers PVC spiral wrap and Scotch 24 screen. The minimal delay was 10us and sensitivity for small targets was more bad. With 15" x12" DD coil, minimal first delay is 5us.

Hello. I want to make a homemade DD coil. The coil is a TX-300mkG. What is the minimum inductance for the RX coil, given the R3, R4, and R5 resistors? I've soldered the circuit and am waiting for the MOSFETs to arrive.

[AhmatAhmatov1959]

Hello. I assembled this circuit on two printed circuit boards.The RX board is assembled separately. Although the circuit diagram was correct, the pulse frequency was 737 Hz for some reason. I reduced resistor R60 to 18 kOhm, resulting in a frequency of 1400 Hz. The current consumption of the transmitter board was 400 mA. To reduce the current to 200 mA, I added a 6 ohm resistor to the coil.Without the coil, the current consumption was 50 mA. The TX coil is a homemade 280 mcg, 1.2 ohm, 21 cm in diameter ring. I wanted to ask what is better: leaving the resistor in series with the coil or increasing the resistance of resistors R1 and R44. I also increased the resistance of R24 and R25 to 500 ohms. This increased the reverse voltage of the pulse from 120 V to 400 V, and for some reason the duration decreased to 5мкс.If anyone has built this circuit, I'd like to know the TX current consumption and how it can be reduced in another way. Thanks for the reply.

[Detectorist#1]

Hi Ahmat,
This project is for DD type of coil and the values of R24,R25 and R3 are optimized for min delay before target pulses. The values of R1 and R44 have to rest 1oHm. Current consumption is reduced by shorter TX pulse. The duration of the TX pulse depends on the value of R57. When you want to use MONO coil, the values of R24 and R25 have to be optimized for achieving of min delay before TGT pulses. In this case, R3 have to be omitted. In my experiments with 300uH MONO coil, the min delay is 10us instead of 5us with DD coil. Have in mind this will reduces the sensitivity for small targets.

[pechkata]

Hello. I assembled this circuit on two printed circuit boards.The RX board is assembled separately. Although the circuit diagram was correct, the pulse frequency was 737 Hz for some reason. I reduced resistor R60 to 18 kOhm, resulting in a frequency of 1400 Hz. The current consumption of the transmitter board was 400 mA. To reduce the current to 200 mA, I added a 6 ohm resistor to the coil.Without the coil, the current consumption was 50 mA. The TX coil is a homemade 280 mcg, 1.2 ohm, 21 cm in diameter ring. I wanted to ask what is better: leaving the resistor in series with the coil or increasing the resistance of resistors R1 and R44. I also increased the resistance of R24 and R25 to 500 ohms. This increased the reverse voltage of the pulse from 120 V to 400 V, and for some reason the duration decreased to 5мкс.If anyone has built this circuit, I'd like to know the TX current consumption and how it can be reduced in another way. Thanks for the reply.

No one has ever built this scheme - you are the first.
It's all in theory.

[AhmatAhmatov1959]

No one has ever built this scheme - you are the first.
It's all in theory.

Hello. I'd be glad if you started too. I find the circuit interesting. What I can't figure out is why, when increasing the resistance of R24 and R25 to 500 ohms and increasing the surge voltage to 400 volts, the coil's decay time decreases to 5 µs. Could you explain this to me?

[Detectorist#1]

Hi Ahmat,
It is interesting where you measured these 5us - on the coil or before sampling integrators (pin 7 of U1B)?

[AhmatAhmatov1959]

Hi Ahmat,
It is interesting where you measured these 5us - on the coil or before sampling integrators (pin 7 of U1B)?

Hello. I measured the coil. I have the RX circuit assembled, but I haven't connected it yet because I wanted to make sure the power supply and TX circuit were working properly. Resistors R1 and R44 are marked as 1 ohm in the circuit, but I'm currently changing them to 10 ohms. I wanted to reduce the return pulse time, so I shorted resistor R25. The voltage dropped from 120 volts to 60 volts, and the pulse lengthened.Then I gradually increased the resistance of resistors R24 and R25 to 500 ohms. The pulse voltage became 400 volts, and the time decreased to 5 µs. I think this may be related to the transistors. I bought 20 IXTP10P50P transistors, and one of them had a capacitance of 1.7 nF. The N-channel transistor had a capacitance of 1.67 nF. The resistance of both is also almost the same: 1-1.2 ohms. I wound the TX and RX coils. Measuring the TX coil without a cable on a Chinese tester showed a frequency of 1.8-2.7 MHz. This gives a capacitance of 40 pF. I bought an antenna cable with internal insulation made of porous polyethylene or polypropylene and replaced the inner core with 13 wires with a diameter of 0.2 mm, winding 24 turns. I'll be using a DD coil, but I'll move U1 to the coil. Thank you so much for the circuit design.

[Detectorist#1]

Hi Ahmat,
My serious advice to you: First repeat the entire scheme without changes and then, if you have any problems, write to me.

[AhmatAhmatov1959]

Hi Ahmat,
My serious advice to you: First repeat the entire scheme without changes and then, if you have any problems, write to me.

I'll do that. I just removed the 5-ohm series resistor from the coil and installed R1-5 and R44-5ohm. The current consumption is back to 400mA, which I don't understand. I'll increase R1 and R44. It's a very interesting circuit.

[Detectorist#1]

Not increase the values of R1 and R44 !!!!!!! This will have as result not property controlling of TC4428CPA and un-controlled current via two power MOS transistors !!!!!. For lowering of the supply current reduce the value of R57.

[AhmatAhmatov1959]

Not increase the values of R1 and R44 !!!!!!! This will have as result not property controlling of TC4428CPA and un-controlled current via two power MOS transistors !!!!!. For lowering of the supply current reduce the value of R57.

It's been running for an hour now with a resistance of 40 ohms each, nothing's burning or heating up. Current consumption is 220 mA. Voltage on the coil is 600 volts. 5 µs. R24 + R25 --- 800 ohms. When my daughter gets home, I'll post a photo. I don't know how to do this myself. Sorry, but I get genuine pleasure from the process, without even understanding why this happens.

[Detectorist#1]

Wish you success!

[pechkata]

Hello. I'd be glad if you started too. I find the circuit interesting. What I can't figure out is why, when increasing the resistance of R24 and R25 to 500 ohms and increasing the surge voltage to 400 volts, the coil's decay time decreases to 5 µs. Could you explain this to me?

I don't plan on making the schematics for this airframe.
Everything is a fabrication.
He's looking for someone to get his mind around - someone like you.

[AhmatAhmatov1959]

I don't plan on making the schematics for this airframe.
Everything is a fabrication.
He's looking for someone to get his mind around - someone like you.

I'm very happy for him. He found me!!! It's a shame you don't want to build it. With your experience and knowledge, it's much easier than mine. The circuit is interesting. I think you'll change your mind in a week. The power supply and TX unit are already working. Now I'm connecting the circuit with the RX; I have it assembled.