Surfpi 1.2 with whites TDI coil

[Malospelos]

Good morning guys, I would like to know if anyone has tried a TDI Whites coil on the Surfpi 1.2.

Specifically, the coil is Dualfield 7.5". I have one for very little money.
Thank you very much for your answers.

[Pete61]

Its almost certainly not going to be plug-and-play.
According to the patent https://patents.google.com/patent/US7994789B1/en
Theres 2 damping resistors, one inside the coil housing for the smaller inner coil and one external in the head unit for overall damping.
Its a series connected array, so maybe theres only 2 wires going to the coil head, either way, Im pretty sure you're going to need an oscilloscope to size the external damp resistor correctly.

[Carl-NC]

I've never tried it, but probably it's close enough that it will work.

[Malospelos]

Thank you very much for your answers, I have an oscilloscope and the coil is not yet available to measure the inductance. I will keep you informed. I had read that they measure 300mh, the only thing is the DualField model and as you say there are two coils, it is not the Mono model.

[Carl-NC]

The DF coil should also be close to 300uH overall. The SMPI coils are typically around 250uH, so 300uH will probably work.

[bklein]

I have, no issue. Try adjusting the damping resistor value such that the waveform you get has an immediate “ bump” that rises up to nominal level. Normally you try to minimize this but letting it come up really improved the coil sensitivity. I did this on my dual field, pi pro, and surf pi. The detector runs differently, the gain can be raised.Hard to describe.

[Malospelos]

Thank you very much, having two coils more or less I think (I don't have the coil yet), I understand that you use both at the same time or they are connected to each other, do you remember what damping resistance you put in? in? ? ? It would be a great help because I have measuring devices but I have no experience, I am a newbie eager to learn. All answers are appreciated, I have managed to make a pointer with a ferrite rod and a Litz wire. It works well but is not very sensitive to many things. small, it measures 300mh, I don't know if the detector is not made for such small things or the probe is bad.

[Pete61]

Thank you very much, having two coils more or less I think (I don't have the coil yet), I understand that you use both at the same time or they are connected to each other, do you remember what damping resistance you put in? in? ? ? It would be a great help because I have measuring devices but I have no experience, I am a newbie eager to learn. All answers are appreciated, I have managed to make a pointer with a ferrite rod and a Litz wire. It works well but is not very sensitive to many things. small, it measures 300mh, I don't know if the detector is not made for such small things or the probe is bad.

Basically the inner and outer coils are connected in series with a damping resistor across the start and end of the small inner coil.
The coil pos on the Pi pcb goes to the start on the larger outer coil and the coil end goes to the start on the small inner coil, with its coil end going to the ground/neg of the coil connection on the pcb.

Surf Detector breaks it down in his vid. ( Dual Field Coil DIY project for PI Detector)

Ive just built one yesterday using 0.5mm stranded ethernet cable, 300mm dia with 14T and 178µH.
The small one was about 17T, 135mm dia at 98µH.
I used a 411Ω on the small coil and 910Ω on the large one.
I solder my resistors on the coils and not pcb, that way I can swop coils out in the field without having to carry a bunch of plug and play resistors on dupont connectors.
I had a 5µS pulse width on the small coil and once everything was joined, about 6µS overall.

If you can make it work on the Surf PI, Im sure you'll be quite happy with it.

[Malospelos]

Good morning friends, the coil that I bought second-hand has finally arrived.

Coincidentally, it almost matches the Surfpi standard and I only had to move the Offset a little to leave it at 0V.

Now I receive a 25 cm 10 euro cent coin.
A 60mm diameter lid at 40cm well marked (45 with low threshold)
It's a Tdi DualField coil, I think it's not bad for such a small coil.

I wanted to ask because I don't understand well, if the damping resistor is used to adjust the circuit with the coil to 0V, and we have to change R6 when it is outside that range and cannot be adjusted with compensation (OFFSET P1). I have seen that there is an invention to be able to configure the damping resistance, but I don't know what it should get me if I modify it. I don't know where I should measure with the oscilloscope or what exactly I should get. Can someone tell me where to place the clamp and what size I should take or what is ideal for it to come out well?

Now I know that I have to measure with a multimeter and get 0V ground to pin 6 of Ne5534.

Thank you very much for your time, I am learning through trial and error.

[Pete61]

Good morning friends, the coil that I bought second-hand has finally arrived.

Coincidentally, it almost matches the Surfpi standard and I only had to move the Offset a little to leave it at 0V.

Now I receive a 25 cm 10 euro cent coin.
A 60mm diameter lid at 40cm well marked (45 with low threshold)
It's a Tdi DualField coil, I think it's not bad for such a small coil.

I wanted to ask because I don't understand well, if the damping resistor is used to adjust the circuit with the coil to 0V, and we have to change R6 when it is outside that range and cannot be adjusted with compensation (OFFSET P1). I have seen that there is an invention to be able to configure the damping resistance, but I don't know what it should get me if I modify it. I don't know where I should measure with the oscilloscope or what exactly I should get. Can someone tell me where to place the clamp and what size I should take or what is ideal for it to come out well?

Now I know that I have to measure with a multimeter and get 0V ground to pin 6 of Ne5534.

Thank you very much for your time, I am learning through trial and error.

The P1 offset trimmer is only used to adjust 0v and it is left alone, changing R6 doesnt affect the 0v in my experience.
It stays 0v even when changing different coils, but I usually check just to make sure.

You can only get the ideal Rdamp with an oscilloscope and a variable resistor jig connected to R6 position next to the mosfet.
Surf Detector describes the jig in his video https://www.youtube.com/watch?v=CrJ5tFFmWyo

[Malospelos]

Thank you very much for the answers and giving me your time.

I connect the oscilloscope to TP1 and TP2, right? channel 1 and two.
I am new to the oscilloscope, I have seen and translated those videos and I am learning but there are things I don't know, sorry for my ignorance.

Is that how I say?

And will the two waves appear on the screen?

with resistance of
damping, do you move the position wave on the x-axis, so to speak?

[Malospelos]

This is what the waves should look like from what I understand in the videos.

[Pete61]

Thank you very much for the answers and giving me your time.

I connect the oscilloscope to TP1 and TP2, right? channel 1 and two.
I am new to the oscilloscope, I have seen and translated those videos and I am learning but there are things I don't know, sorry for my ignorance.

Is that how I say?

And will the two waves appear on the screen?

with resistance of damping, do you move the position wave on the x-axis, so to speak?

with resistance of damping, do you move the position wave on the x-axis, so to speak?

No, you change the width of the pulse at TP2, short width= faster which is what you want to detect faster decaying metals like gold.

The 2 pulses appear on screen yes.
You typically want the delay pulse to end just as the coil output pulse starts rising, because thats when your sample pulse starts listening.

Here is min delay pulse using the delay pot


Here is max delay pulse using the delay pot





here is the main sample "listen" pulse taken off pin 13 of U7 the CD4066.
As you can see it begins where the delay pulse ends.


Basically, once I have the delay pot set to where I like it, I mark the position on the dial face with the coil dia or µH value if I have more than 1 of the same dia.

[Hinkri]

The DF coil should also be close to 300uH overall. The SMPI coils are typically around 250uH, so 300uH will probably work.

250 uH is this data for a single coil or a double one? And what is the coil resistance and wire diameter of the original coil?

[Malospelos]

Good morning everyone, thank you for taking the time to respond.

The other day I was testing the oscilloscope and playing with it, I'm still learning how to use it.

Thanks for the photos of the waves and taking that trouble, the 7.5" TDI coil works very well. And it has good depth for its small diameter.

I need to know how to make the wave on the oscilloscope slow down.

Thank you all