Bipolar PI MD with GB and DD Coil

[Detectorist#1]

Hi pito,
Yes, no problem to replace two simple IC (for under 1 USD) with ESP32 for generating of 5 different pulses. Just, maybe for some people with no big experience with using of microprocessors will be more easy to repeat my project. And, you are right, generating of sound as result of the target's signal will be more simple with using of the possibilities of the microprocessor. Generally, my idea was to propose the scheme of relatively good Bipolar PI MD for people without big experience, no more.

[Detectorist#1]

Hi pito,
It will be solution for book of records if you propose solution for bipolar PI MD without using of two MOSFETs.

[pito]

In my opinion, this isn't a PI metal detector, but an induction balance, at least it utilizes its operating principle. The main element of a PI detector is a resistor that attenuates and processes the signal. Your circuit uses bipolar pulses, but I don't see the benefit.


PI MD without using of two MOSFETs. = circuit below, replace the motor by coil

[Carl-NC]

PI MD without using of two MOSFETs. = circuit below, replace the motor by coil

What you show would be a square wave drive for a VLF detector, not PI. The circuit posted by Detectorist#1 is true PI, not VLF.

[GeoMax]

In my opinion, this isn't a PI metal detector, but an induction balance, at least it utilizes its operating principle. The main element of a PI detector is a resistor that attenuates and processes the signal. Your circuit uses bipolar pulses, but I don't see the benefit.


PI MD without using of two MOSFETs. = circuit below, replace the motor by coil

Hi Pito,

Your example also includes MOSFETs. See the TC4424 datasheet.

[pito]

true PI, not VLF.

he doesn't use it .....

[pito]

[pito]

What you show would be a square wave drive for a VLF = That what he did, short pulses in the induction balance detector, similar circuit IB above.

[Carl-NC]

What you show would be a square wave drive for a VLF = That what he did, short pulses in the induction balance detector, similar circuit IB above.

The circuit in post 97 is VLF, not PI. It uses a Colpitts oscillator to produce a sinusoidal TX signal, not pulse.

I think you are getting confused because the circuit Detectorist#1 has proposed uses an induction balance coil. PI can use IB coils, same as VLF, but they are still very different circuits. In fact, his circuit does not require the coil to be induction balanced, you can lay the RX coil directly on top of the TX coil, no balance necessary. Probably it will work with a mono coil as well. Neither of these will work for a VLF circuit.

[Detectorist#1]

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.

[pito]

The circuit in post 97 is VLF, not PI. It uses a Colpitts oscillator to produce a sinusoidal TX signal, not pulse.

That what I am saying, he replaced sine wave by short pulses, (there is no damping resistor = classic component of PI ) , rest of the circuit it is classical IB.

[pito]

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.

Can you post a video ?

[pito]

Carl-NC
It is not convenient to use a quote, I have highlighted a small fragment of the original message, but it displays the entire message, so it is difficult to determine which sentence the reply refers to.

[Carl-NC]

That what I am saying, he replaced sine wave by short pulses, (there is no damping resistor = classic component of PI ) , rest of the circuit it is classical IB.

R24+R25 is the damping resistor. The demods are sample-hold style as often used in VLF designs, and even though most PI designs use sampling integrator demods (I don't know why), either way works fine.

[pito]

My apology, I overlooked that.