Bipolar PI MD with GB and DD Coil

[AhmatAhmatov1959]

Wish you success!

Hello. As you recommended, I reduced the R57 resistor to 59 ohms. More precisely, I set the constant resistor to 39 ohms and the variable resistor to 20 ohms. Before the changes, the TX was 200 µs; now it's adjustable between 50 and 100 µs. Resistors R1 and R44 are 5 ohms. The metal detector's current consumption with the coils connected is now 220 mA. The main thing is that the metal detector is working. Its metal sensitivity is good, but it needs some adjustment. I need to finish the DD coil. I'm posting a photo showing how I shorted a 925-ohm resistor with a utility knife, It is clear that when the resistance R24 R25 decreases to 94 ohms, the voltage decreases and the duration of the reverse pulse increases. My current resistor is R24 + R25 = 700 ohms. I have a few questions for you. 1. Is it possible to increase the pulse voltage by replacing the STTH1L06 diodes with higher-voltage ones? 2. Please recommend a low-frequency amplifier, as I don't have a 150-ohm speaker. 3. How to increase the reaction speed of a metal detector The most interesting thing is that the microcircuits are all Chinese, and I examined them with a TL062 and TL072 oscilloscope. They were defective, but the circuit works.Thank you so much for developing this scheme.

[Detectorist#1]

Hi Ahmat,
The duration of the TX pulse depends from the values of the capacitor C34 and resistor R57 (T=0.75RC ) in the input of U9B. The value of C34 is 1nanofarad. The value of the R57 is 130 kilo-oms. The pulse is =0.75 x 1nF x 130K = 97.5us. The values of 59 ohms and 20 ohms at this place are very strange! Maybe your capacitor C34 haves value of 1 microfarad, not 1 nanofarad. Check this again please. This mistake explains the lowering of the frequency of the generator with U9a.
Now for your questions:
1. The peek voltage depends from the peek current of the coil and from the value of R24+R25 resistors. The change of STTH1L06 with 800V or 1000V diodes will not change the peek voltage.
2. The noise on the power supply lines ( -8V and GND) as result of the sound, influences on the work of the rest parts of the detector. The change of the type of the audio amplifier will not solve the problem. Only solution is to use 150 ohms speaker. This allows the reducing of the current for audio amplifier and the parasitic influence.
3. I know, the reaction speed is very slow ( big recovery time after sensing of near big target). Now, I work on this problem very intensive. One possible solution is the idea in White's TDI MD, but I look for more simple solution.

[AhmatAhmatov1959]

Здравствуйте Detectorist#1. I re-soldered the TX board. The schematic is correct. All the Chinese CD40106s turned out to be defective. They all have different pulses and different frequencies. I selected one with a 100 µs pulse and a frequency of 1000 Hzand which does not have a GB Strobe pulse. The IXTP transistors are also defective; they show normal on the tester, but when connected to the circuit, the current consumption increases to 1 amp. I measured the current on the coil through a 0.1 ohm resistor. The pulse current is 1.5 amps. Please tell me what current the coil should be drawingand how many microseconds should there be between pulses . Thank you.

[Detectorist#1]

Здравствуйте Ahmat!
With 100us TX pulse and 300uH TX coil, the peek current pulses of N-ch MOS and P-ch MOS are 2.2A. The total current consumption depend from TX frequency. What is the real value of C34 - 1nF or 1uF? The missing of GB pulse is strange - check carefully the connections and the values of the parts.

[AhmatAhmatov1959]

Здравствуйте Ahmat!
With 100us TX pulse and 300uH TX coil, the peek current pulses of N-ch MOS and P-ch MOS are 2.2A. The total current consumption depend from TX frequency. What is the real value of C34 - 1nF or 1uF? The missing of GB pulse is strange - check carefully the connections and the values of the parts.

Capacitor C34 turned out to be 1nF, so I replaced it with a SD40106. Each one had different pulse lengths, from 50 µs to 400 µs. The frequency also varied from 700 Hz to 1600 Hz. Only one chip gave 100 µs with the component values according to your schematic. I buy components from AliExpress. Because of sanctions, the Chinese are selling nothing but defective parts.Russian companies sell the same thing, only at a much higher price, and you have to wait two months for your order to be fulfilled. I built three metal detectors— this , a Tesoro Lobo, and a Magpi—and threw away over 50 microchips. Instead of the IXTP10P50P, I installed an MTP2P50G for an experiment. It ran for over an hour without heating up. Resistors R24 and R25 are 250 ohms each. One pulse is 400 volts, and the other is 500 volts. Duration is 3 µs. Please advise how to make them equal. Preferably 500 volts each.

[Detectorist#1]

Hi Ahmat,
For equal positive and negative peek voltage, the sum of Rds of N-ch MOSFET + R34 have to be equal to the sum of Rds of P-ch MOSFET + R15.
What is this strange duration of 3us? What is the value of R57 when TX pulse =100us?

[AhmatAhmatov1959]

Hi Ahmat,
For equal positive and negative peek voltage, the sum of Rds of N-ch MOSFET + R34 have to be equal to the sum of Rds of P-ch MOSFET + R15.
What is this strange duration of 3us? What is the value of R57 when TX pulse =100us?

Hello, Detector #1. P57 = 130kΩ. All component values match your schematic, except for resistors R24 and R25. Mine are 250 ohms. I already asked why increasing these resistors increases the reverse voltage and thedecreases pulse duration.It should be the other way around. With R24=47 ohms and R25=47 ohms, as per the diagram, the pulse voltage is 190-200 volts, and the pulse is damped in 10 µs. The coil is a homemade ring; I'll be making a DD out of it.

[pechkata]

Hello, Detector #1. P57 = 130kΩ. All component values match your schematic, except for resistors R24 and R25. Mine are 250 ohms. I already asked why increasing these resistors increases the reverse voltage and thedecreases pulse duration.It should be the other way around. With R24=47 ohms and R25=47 ohms, as per the diagram, the pulse voltage is 190-200 volts, and the pulse is damped in 10 µs. The coil is a homemade ring; I'll be making a DD out of it.

Because the designer has never worked on Pulse pumping - it's all theory...

[AhmatAhmatov1959]

Потому что проектировщик никогда не работал над импульсной накачкой — это все теория...

Привет, pechkata . Я не понимаю теорию. Я умею собирать и паять, и рад за тех, кто умеет проектировать и рассчитывать. На опубликованных фотографиях всё показано, но часто бывает, что практика противоречит теории. А объяснить никто не хочет или не может.

[Orbit]

'Emile, are you Detectorist 1?

[Orbit]

https://youtu.be/b02WAKfHNaU?si=kqbg7OFBssF-lUOO https://youtu.be/faNnogvEM3E?si=SyQgvN_Yz-YXR9IJ https://youtu.be/R03u7VtPdHs?si=G-FeCABBK22csbd6

[Detectorist#1]

Hi pechkata,
If this is not so hard for you, try to be more constructive, not destructive.

[pechkata]

[AhmatAhmatov1959]

Привет, Ахмат!
Для равенства положительного и отрицательного пикового напряжения сумма сопротивлений Rds N-канального МОП-транзистора + R34 должна быть равна сумме сопротивлений Rds P-канального МОП-транзистора + R15.
Что это за странная длительность 3 мкс? Каково значение R57, когда импульс передачи = 100 мкс?

Привет , Детекторист#1 . Пожалуйста, ответь. Рядом с подстроечным резистором R12 стоит метка NULL. Что это значит?

[Qiaozhi]

Привет , Детекторист#1 . Пожалуйста, ответь. Рядом с подстроечным резистором R12 стоит метка NULL. Что это значит?

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