Best homemade PI detector

[zzy]

Hi,
I had made Gary's Pulse-2,i use 8 inch coil. It can detect a small gold ring at 22cm.A coke at about 55cm.
Now my question is: Which PI detector is th best depth for detect gold ring? Delta Pulse or XR-71 or Hammerhead? or the other?
Let's tell the best depth use middle coil(8 inch).

sorry my bad english.

[kt315]

you put all eggs in one basket. Delta Pulse and XR-71 are slow-motion detectors for deep big targets. those are used only with huge coils.

kinda regards

[zzy]

you put all eggs in one basket. Delta Pulse and XR-71 are slow-motion detectors for deep big targets. those are used only with huge coils.

kinda regards

Hi kt315
Do you konw which PI detector is for coin hunting.And it's suit for homemade.I mean the detector is not noly my mentioned before.

[Max]

Hi,
you can use all you reported for coins too... but have to change timing and tune components.

For example I used XR71 for beach hunting with 8'' coil too and works cool if you match requirements. Sure, its natural role is in deep , slow search like KT315 told you, so if you don't accomodate timing you'll end-up with useless device.

The best homemade PI ??? Probably the GS4 is the best if you can do it, no single-side/troughhole PCB is available to the public, but can find SMT kind and it's complex and tricky design...tricky tuning, hard stuff (probably the most difficault PI project ever approached on this forum and others too). But detection is great, if not enormous , once tuned properly... if you can tolerate or haven't e.g. bricks and similar stuff... that make it sound like if there's metal!

For example, a cigarette box sized red brick fragment you can detect from 40cm ...so forget about searching in places with many of them.

Real performance on 8'' ??? Depends on you! Your ability to make fast , good monocoils is a key factor to success. But sure, I can say, is more than most of currently sold PIs. Detector is extremely sensitive to gold, even small things like smaller rings... but also to aluminium stuff, so you need "clean" soil or to search on the beach, otherwise is wasted time.

Kind regards,
Max

[ivconic]

Yes Delta Pulse can be made to work at 450-500Hz frequency and with small diammeter coil (20cm,24wind,0.4mm wire). And it is suitable for locating very small items at shallow depths (up to 40cm in soil). IRF740 need good heatsink. Coil MUST have Al cage (Faraday cage). Cage must be connected to batt. + pole (through cable - cable shield, litz)....and voila!
In the past i checked this configuration and works splendid!
But...since you have here few excellent VLF projects to build, i dont think PI is best solution for coin hunting. Anyway you want...
Cheers!

[kt315]

a note

Delta Pulse can be made to work at 450-500Hz frequency

in a category of PI detection, it mean not a frequency. but PULSES-PER-SECOND. we say PPS, for example 450 PPS, it is due what you describe.
trully yours.

[ivconic]

When i touch TR2 test point on DP pcb with my frequency meter probe, it reads 450 Hz.....so logically i am saying the facts i saw on that funny small LCD display....
PPS...pulse per second. I agree. KT315, please define me the term "frequency"!

[ivconic]

Yup, look what i found;

Frequency refers to "the number of cycles or completed alternations per unit of time." In general, frequency means some count per unit of time. In behavior analysis the most common measure of frequency has been responses per minute. In behavior analysis, frequency often gets renamed as "rate" or as "rate of response."
Cooool!

[zzy]

Yes Delta Pulse can be made to work at 450-500Hz frequency and with small diammeter coil (20cm,24wind,0.4mm wire). And it is suitable for locating very small items at shallow depths (up to 40cm in soil). IRF740 need good heatsink. Coil MUST have Al cage (Faraday cage). Cage must be connected to batt. + pole (through cable - cable shield, litz)....and voila!
In the past i checked this configuration and works splendid!
But...since you have here few excellent VLF projects to build, i dont think PI is best solution for coin hunting. Anyway you want...
Cheers!

Hi ivconic
I often search on the beach.Wet sands.VLF is not suitable.
I use small diammeter coil because it's pinpoint is good.
You mean the small diammeter coil need a AL shield?
very thanks.

[Max]

Hi ivconic
I often search on the beach.Wet sands.VLF is not suitable.
I use small diammeter coil because it's pinpoint is good.
You mean the small diammeter coil need a AL shield?
very thanks.

Hi,
can I answer ? yes, you need it otherwise you'll be submerged by capacitive effects at coil... and will get lot of false signals.

I've used unshielded coils for e.g. dry sand but it's a stupid solution to me , totally... if I can get full stability just adding a faraday shield there.

In some older PI project I saw often that you don't require shield on coil... etc... and that's true for many deep seekers like delta pulse with 1mx1m coil: you suspend coil high, far from soil... so there are no capacitive effects (well, they are minimal about impact on working of device, not relevant) you can see and so no false signals (ideally, but not always so).

On smaller coils you can avoid shields if first delay is high... something 35-50uS...this way e.g. wet sand will not make sound detector (these ranges are still used in underwater PIs) but on ALL real coin devices PIs for beach hunting you have smaller 1st delay, in some you have the 10-15uS range... and so the response to e.g. a large conductive layer (wet sand and salt water...) will be enhanced to a point you'll get instability due to capacitive effects: this doesn't happen on dry sand... so there you can use the unshielded coils like I wrote above.

Now, you need extremely low 1st delay to get good sens to small gold and other small stuff so you are actually forced using 10-15us there or miss too much good stuff, then you need ALWAYS the shield on the coil, if you plan to use detector on wet sand also like it's normal for beach hunting.

If you read the BBsailor's article on fast monocoils you'll get the picture of what you need and why, with all calculations.

Kind regards,
Max

[zzy]

Hi,
can I answer ? yes, you need it otherwise you'll be submerged by capacitive effects at coil... and will get lot of false signals.

I've used unshielded coils for e.g. dry sand but it's a stupid solution to me , totally... if I can get full stability just adding a faraday shield there.

In some older PI project I saw often that you don't require shield on coil... etc... and that's true for many deep seekers like delta pulse with 1mx1m coil: you suspend coil high, far from soil... so there are no capacitive effects (well, they are minimal about impact on working of device, not relevant) you can see and so no false signals (ideally, but not always so).

On smaller coils you can avoid shields if first delay is high... something 35-50uS...this way e.g. wet sand will not make sound detector (these ranges are still used in underwater PIs) but on ALL real coin devices PIs for beach hunting you have smaller 1st delay, in some you have the 10-15uS range... and so the response to e.g. a large conductive layer (wet sand and salt water...) will be enhanced to a point you'll get instability due to capacitive effects: this doesn't happen on dry sand... so there you can use the unshielded coils like I wrote above.

Now, you need extremely low 1st delay to get good sens to small gold and other small stuff so you are actually forced using 10-15us there or miss too much good stuff, then you need ALWAYS the shield on the coil, if you plan to use detector on wet sand also like it's normal for beach hunting.

If you read the BBsailor's article on fast monocoils you'll get the picture of what you need and why, with all calculations.

Kind regards,
Max

HI Max,

Excellent answer! Now i know i need a shield.My delay time is 16us. In
wet sand and salt water area,it's a little instability.
You mentioned GS4,do you made one? Can you give me a link?
Thanks you reply.

[Max]

HI Max,

Excellent answer! Now i know i need a shield.My delay time is 16us. In
wet sand and salt water area,it's a little instability.
You mentioned GS4,do you made one? Can you give me a link?
Thanks you reply.

Hi,
yes, I made it on protoboards stuff... etc... the schematics is somewhere here but I forget where exactly, you could try with a simple search.

I have made using original schematic by Alexis, but have this pdf file with the PCB design too.

Kind regards,
Max

[Max]

here some links

https://www.geotech1.com/thuntings/s...light=goldscan

https://www.geotech1.com/thuntings/s...light=goldscan

here original schematic I think:

https://www.geotech1.com/thuntings/s...light=goldscan

please nothe the original schematic had little errors then corrected later...like pot with central lead disconnected and the like; timing section is ok, simulation was wrong due to an error occurred in LTspice (if I remember well porkluvr made sim of oscillator)

Kind regards,
Max

[zzy]

here some links

https://www.geotech1.com/thuntings/s...light=goldscan

https://www.geotech1.com/thuntings/s...light=goldscan

here original schematic I think:

https://www.geotech1.com/thuntings/s...light=goldscan

please nothe the original schematic had little errors then corrected later...like pot with central lead disconnected and the like; timing section is ok, simulation was wrong due to an error occurred in LTspice (if I remember well porkluvr made sim of oscillator)

Kind regards,
Max

Hi Max

If you have please send me the pcb of goldscan4.
If no,I'll design one.

my email:[email protected]


Kind regards

[kt315]

PPS...pulse per second. I agree. KT315, please define me the term "frequency"!

no dilemma to define. but please what Guru has said you are able to penetrate?

Re: Pulse Frequencies- your choice?
Eric Foster
Date: July 06, 2002 03:15AM

Hi Gaz,
Fundamentally, the signal from an object is the same whether a PI detector operates at 1 pulse per second, or 10,000 pulses per second. The very first PI detectors used pulse rates of less than 100, while today’s units generally pulse in the 1000’s. The Goldquest that I produce has a maximum pulse rate of just under 10,000. So why are different pulse rates used? It is more to do with response speed and electromagnetic interference reduction. Detectors with low pulse rates tend to be more prone to power line interference and have a slow build up and decay of the audio or visual signal. Ones with high pulse rates are not greatly affected by power lines but can be subject to interference from low frequency radio transmitters. However, the provision of a frequency shift control can overcome this.
A detector designed for locating tiny objects must have a fast response, otherwise the coil can pass over the object before the output circuits respond. This is because some averaging of the sampled receiver signal is necessary to smooth out any residual noise and provide a dc level to operate the output circuits. The more samples per second that are available, the faster this can happen.
What is important from the objects point of view, is the duration of the transmitter pulse and it’s rate of switch off. This, as I understand it, is what the SD’s use. Two different transmitter pulse widths, with the narrower pulse being repeated three or four times. Because the narrow pulses are much lower amplitude (if you look at the coil current), perhaps the three, or four, receiver signals are summed to give a similar amplitude to the receiver signal in the wide pulse channel, so that it can be subtracted for ground cancelling. This is just a guess, so I am open to correction on this.
Switch off rate is important, particularly if you are looking for tiny, or poorly conductive objects. Ideally the switch off should be at least a fifth of the object time constant. A fast, clean, switch off also means that receiver sampling can take place earlier, to capture the fast decays from small targets.
Another point regarding pulse rate, is that the higher this is, the greater the drain on the power source. For a given pulse width and transmitter current, the pulse rate has to be balance against acceptable battery operating time.
Eric.

PI Terminology
Eric Foster
Date: March 26, 2000 03:32PM

PULSE WIDTH. The width of each individual transmitter pulse. Depending on the detector and its intended application, the pulse width can vary between 50 microseconds (uS) and 1000uS. 50 to 150uS is usually the width for ring and coin size objects while wider pulses suit detectors designed for locating larger objects. A boat towed PI designed to look for cannons would likely use 1000uS. Examples are:- Whites Surfmaster 50uS, Deepstar 100uS, Aquapulse 300uS, Superscan and Aquapulse towed 1000uS.
PULSE FREQUENCY or PULSE REPETITION RATE. The number of times the transmitter pulse is repeated every second. The frequency affects the response speed, power consumption and interference rejection, although all of these are influenced by many other factors in the circuit design. Examples are:- Surfmaster 800 pulses per second (p.p.s.) Deepstar 3000 p.p.s. Aquapulse 170 p.p.s. Superscan 66 p.p.s.
PULSE DELAY. The time that is allowed to elapse between the transmitter switching off at the end of each pulse and the start of the receiver function or receiver sample pulse. The shorter this time is, the higher the sensitivity to smaller and/or poorer conductors. On some PI detectors (Deepstar) this is called a REJECT control. The shortest pulse delay is with the control on MIN and if it is turned clockwise the pulse delay time is lengthened which enables bits of foil and pulltabs to be rejected. However, thin and lower carat rings may also be lost. For beach work on salt wet sand a minimum pulse delay of 15uS is about right so as not to get too much signal from the conductive salt water. Detectors for diving have to use longer delays as the water signal is much greater. Detectors for large objects, as well as a long TX pulse, use longer delays to minimise signals from small bits of metal.
DECAY TIME or OBJECT DECAY. The time that the small electric current induced in a metal object flows. The energy is dissipated in the electrical resistance of the object so that poorer conductors (higher resistance) have a shorter decay time. A thin ring may have a decay time of 50uS while a silver cob could be 500uS. A detector set with a pulse delay of 100uS would pick up the cob but not the ring.
SAMPLE PULSE or SAMPLE WINDOW. The period of time from the start of receiver sampling to the end of the sampling period. Usually between 15 and 50uS. In the Deepstar it is set at 20uS irrespective of the pulse delay. In the CS7 the sample pulse tracks the pulse delay i.e. it is always the same value as the delay.
DUAL SAMPLING. This is a system used by most PI’s where there is a second sample pulse that occurs much later (a few hundred microseconds) but before the next transmitter pulse. The signal from the second sample is subtracted from the first to give interference cancellation (powerline noise) and also to eliminate the signal from moving the search coil in the earth’s magnetic field. Most of the object signal has gone by then so that object signals are not cancelled.
INTEGRATION TIME. As the received signals are in the form of pulses and these are then sampled in short windows, an averaging system is needed to smooth these out and end up with a d.c. voltage that can operate a meter and/or and audio generator. The integration or averaging time relates to the number of pulses over which the average is taken. With the Deepstar, around 1500 samples are averaged to give the d.c. output. Hence the response time is about ½ second (3000 p.p.s.)