My take on the HH2

[waltr]

Hi Waltr, have you tried your 3 sample GB out in the field yet ?

Just a little sweeping in my yard since the ground is still frozen solid. I did check over the red brick walk but didn't need any GEB added so these bricks may not have enough Iron in them. Even after the weather warms I will need to find a place with mineralized ground. Not much of it around here but have heard that there is some probably around the areas where Iron ore mining took place in the 18th and early 19th centuries. I do know of a few of these locations but they are not local, require a few hours drive.

I have been experimenting with using GEB as a crude reverse discrimination. with GEB added high conductors go low tone/high tone and low conductors go high tone/low tone.

Hi Walr, also would you mind telling me please which fets (Q6/Q7 from sheet 2)
are you driving with S1,S-GEB, S-EFE, thanks.

These are BF256 n-ch JFETS as marked on the schematic.
https://www.onsemi.com/pub/Collateral/BF256A-D.PDF

Most small signal JFETs should work but an Analog switch, 4066, etc, should work better.
I have also tried 2N3819 (similar but different pin-out).
https://www.onsemi.com/pub/Collateral/2N3819-D.PDF

[waltr]

20cm (8") Concentric coil

This is another type of Induction Balance coil consisting of an outer TX coil and an inner RX coil. The IB is achieved by winding a few turns of the TX around the RX coil but in the opposite direction. This Balances or Nulls the TX magnetic field in the RX coil.
Don Bowers explains building these coils very well here:
https://sites.google.com/site/dbcoilshells/home/resources/building-concentric-coils

His coils are for VLF MDs but construction is the same. I just calculated the coils to get around 400-500uH inductance for a PI MD. This turns out to be 27 turns, #28 enamel for TX- 470uH, 4.3 Ohm, 33pF. The RX is 42 turns, #28, 406uH, 2.8Ohm, 58pF. The Buck coil worked out to 7 1/4 turns, 15uH, 0.63 Ohm. Since the Buck coil is wound in opposite direction it subtract from the TX coil inductance. Therefore the effective TX coil inductance is around 450uH. The RX coil inductance is a little low so I may add a few more turns. Some have tried making the RX coil inductance up to twice the TX which increases the RX Signal, sensitivity, but this also increases any Noise pick-up.

Don sandwiched layers of foam board as a coil form. But since I needed way less turn for a PI coil (much lower inductance) I used a single sheet of 1/4" foam board and filed away to foam with a small round file. This created a groove between the cardboard outer layer and a perfect form to wind the coils.
Balance is Tuned by observing the signal at the Pre-amp output on an O'scope and moving the Buck winding lead until it is just over balanced. This is seen as a high level at the beginning of the TX period but dropping to zero before half the TX period is over. See picture " Coils close but over (Large).JPG" in post #6 above). The reason to 'over balance is the phase' information that I plan to measure in an upcoming PIC code version.
The Foam core coils were then put into Don's 8 inch Clam shell.

Coil Photos:





PIC VCO board mounted inside case. Upper, left on side of box.


Main controls with calibration marks. GEB & delay are marked in usec. Threshold marked in SAT amp output Voltage.

[green]

20cm (8") Concentric coil

This is another type of Induction Balance coil consisting of an outer TX coil and an inner RX coil. The IB is achieved by winding a few turns of the TX around the RX coil but in the opposite direction. This Balances or Nulls the TX magnetic field in the RX coil.
Don Bowers explains building these coils very well here:
https://sites.google.com/site/dbcoilshells/home/resources/building-concentric-coils

His coils are for VLF MDs but construction is the same. I just calculated the coils to get around 400-500uH inductance for a PI MD. This turns out to be 27 turns, #28 enamel for TX- 470uH, 4.3 Ohm, 33pF. The RX is 42 turns, #28, 406uH, 2.8Ohm, 58pF. The Buck coil worked out to 7 1/4 turns, 15uH, 0.63 Ohm. Since the Buck coil is wound in opposite direction it subtract from the TX coil inductance. Therefore the effective TX coil inductance is around 450uH. The RX coil inductance is a little low so I may add a few more turns. Some have tried making the RX coil inductance up to twice the TX which increases the RX Signal, sensitivity, but this also increases any Noise pick-up.

Don sandwiched layers of foam board as a coil form. But since I needed way less turn for a PI coil (much lower inductance) I used a single sheet of 1/4" foam board and filed away to foam with a small round file. This created a groove between the cardboard outer layer and a perfect form to wind the coils.
Balance is Tuned by observing the signal at the Pre-amp output on an O'scope and moving the Buck winding lead until it is just over balanced. This is seen as a high level at the beginning of the TX period but dropping to zero before half the TX period is over. See picture " Coils close but over (Large).JPG" in post #6 above). The reason to 'over balance is the phase' information that I plan to measure in an upcoming PIC code version.
The Foam core coils were then put into Don's 8 inch Clam shell.

Coil Photos:
[ATTACH]42042[/ATTACH]
[ATTACH]42043[/ATTACH]
[ATTACH]42044[/ATTACH]
[ATTACH]42045[/ATTACH]

PIC VCO board mounted inside case. Upper, left on side of box.
[ATTACH]42046[/ATTACH]

Main controls with calibration marks. GEB & delay are marked in usec. Threshold marked in SAT amp output Voltage.
[ATTACH]42047[/ATTACH]

Hi waltr, tried one awhile back. http://www.geotech1.com/forums/showt...556#post205556 Interested in how yours compares with a similar size mono.

[waltr]

Hi waltr, tried one awhile back. http://www.geotech1.com/forums/showt...556#post205556 Interested in how yours compares with a similar size mono.

See my post above:
http://www.geotech1.com/forums/showt...561#post239561

This compares a 13" DD, a 10" mono and the 8" concentric with various targets.
I probably will not be making a 8" mono or a 10" concentric so won't be able to make direct comparisons.
Things that I have noticed: This 8" concentric seems to point-pin easier, is more immune to noise, ground,etc, and the Sampling can be much sooner as compared to a Mono coil.

Then from what I have read on various MD forums is this can be a good coil for trashy sites, whereas a Mono works fine at the beach and a DD for non-trashy sites to increase coverage of an area. Still have not yet done any 'real' detecting. Once the weather warms I hope to start testing with real conditions.

[6666]

Hi Walr, also would you mind telling me please which fets (Q6/Q7 from sheet 2)
are you driving with S1,S-GEB, S-EFE, thanks.

Hi Waltr, thanks for the reply but I can see my mistake in how I worded my question, so will try again
what I meant was which fet does each pulse go to, not the type
for example
pulse S1 goes to Q6
pulse S_GEB goes to Q7
pulse S_EFE goes to Q6
Is that clearer ?
thanks.

[waltr]

Hi Waltr, thanks for the reply but I can see my mistake in how I worded my question, so will try again
what I meant was which fet does each pulse go to, not the type
for example
pulse S1 goes to Q6
pulse S_GEB goes to Q7
pulse S_EFE goes to Q6
Is that clearer ?
thanks.

Ahhh...Got it now. Sorry.
That is Correct-
Q6 is turned on by S1 and S_EFE
Q7 is turned on by S_GEB.

A way to tell is Q6 goes to the Inverting input of the Integrator. This inverts the Pre-amp inversion to match the direction of Voltage change out of the Coil.
So this is the "main signal sample".

[Wahyu]

Hi Waltr, I hope you can make a test video, indoor its ok

[waltr]

Hi Waltr, I hope you can make a test video, indoor its ok

I can make a video and post on Vimeo.
What would you want to see in the video?

[green]

New PIC code
A few changes to the PIC code include:
[ATTACH]41806[/ATTACH]

Added a variable delay to the PPS time to avoid interference. Used ADC 2 and made the TX pulse length fixed at 100usec. I was having low frequency wobbles at the SAT output at times. Did notice that when I changes the PPS slightly it could be better or worse. Since the original HH and the TDI have PPS adjust I added this to the code. Then setup and went through the adjustment range (in my basement workshop so lots of AC mains @ 60Hz). As I adjusted the Wobbles were much worse but would nearly go away at some points in the adjustment. So this is a worthwhile code addition. If it is only the AC mains 60Hz interfering then I'll just leave this adjustment as a trim pot inside the enclosure.
The current PPS is 1503 Hz with a minimum 665usec period. The Adjust can add up to 12usec for a minimum PPS rate of 1490Hz.

Ground Balance
Added GEB adjustment, ADC4, then applied the techniques in these threads:
http://www.geotech1.com/forums/showt...-Balance/page3
http://www.geotech1.com/forums/showt...Ground-Balance
I use the Three Sample Method with variable Sample times instead of Variable GB Gain. This can be done on any PI detector with a single differential integrator and a processor for timing. The sequence is:

EFE sample : delay3 : TX pulse : delay1 : Target sample : delay2 : GEB sample

TX pulse fixed at 100usec. Coil Tau = 400uH/ (4 + 10 + 1) = 26usec. 4Tau = 108usec. Coil peak = 0.6Amp.
D1: Delay1 is Pot and variable from 6usec to 35usec.
S1: Target sample set at 15usec (Trim pot adjustable)
D2: Delay2 set at 20usec (Trim pot adjustable)
S-GEB: GEB sample time is adjustable from Target sample time (15us min) to 226usec. This sample time is Target + GEB.
S-EFE: EFE sample time is GEB sample time - Target sample time (0 to 204usec)
D3:delay3 is fixed at 12usec

When GEB control is Zero then the EFE sample time is zero and the GEB sample time = the target sample time. This is the same timing as the original HH sample sequence and allows to turn OFF GEB.
Did some experiments using a 25cm Mono coil and a 33cm DD coil on various targets listed below.
With the GEB time = Zero, all targets respond. As the GEB time is increased then some targets drop into the "GB Hole" and not respond and then respond with a low going signal instead of a high. This change to Low going has been described when GEB is used (White's TDI) so seems like this 3-sample variable time method will work. Big test is when I find some mineralized ground.

Experimented with Delay and sample times as per the second GeoTech link above. This has statements of the timing relationships: S1/D1 = S-GEB /(S1 + D1 + D2) Eq-1
One thing this says is that if D2 (delay between target sample and GEB sample) is longer, then the GEB sample time must be longer. I verify that this is true by adjusting the GEB sample time to find a target's pivot point. Longer D2 delays required longer GEB sample times. This can cause very long GEB & EFE samples which can force slower PPS rates. By keeping the D2 time short (some say that this delay can or should be zero) then the GEB & EFE sample times allow faster PPS rates. Faster PPS rates allow for fast sweeping of the coil across the ground with the same integrator TC.
This showed up in testing when finding the GEB sample time that caused a 'pivot point' on targets. I settled on a D1 time of 20usec which puts the S-GEB time at 67.5usec to satisfy Eq-1.
The pivot S-GEB times for various targets are:
25cm Mono 33cm DD
silver Dime: 23 20
silver 1/2 dollar: 29 18
copper penny: 25 24
Clad quarter: 26 21
sm piece of alum foil: 25 26
1954 Nickel: 170 100
Gold ring: >220 >220
Steel eye screw: 26 negative with no GEB added
Brass key: 45 40
lg alum foil: 122 >220
[ATTACH]41814[/ATTACH]

Therefore, all targets that are close to what the S-GEB is set to will NOT respond and targets that are less then what the S-GEB is set to will produce a Low going SAT output. If S-GEB is set to 67.5us then all of the above targets except Nickel, gold ring and lg alum foil will respond with a Low tone.
This does require an Audio circuit that can produce a Low or High tone like the TDI. I have prototyped a circuit with a full-wave rectified and 4046 VCO chip that does this (schematics posted in the forums here). Am working on replacing the three op-amps and VCO chip with an 8-pin PIC (I'll post details once have this working).

Interesting is that the Pivot points are different for the DD coil verse the Mono coil. The silver and clad coins are about the same but the Steel eye screw is very different.
Played with the different targets again and watched the Pre-amp output on the scope. With a Mono coil all targets increase the Decay time (inverted pre-amp output lowers). However, with the DD coil most targets decrease the delay at the output when at the non-over lapped coils and increase where the coils over lap. Also, during TX ON the different targets cause a very different shape. Tinker showed this in his threads and proposed sampling during TX on as a possible way to obtain discrimination info. Planning on trying this. The steel eye screw produced a response reversed from the other targets.
The a DD coil seems to add more information if there is a High/Low audio tone circuit than a mono coil. An IB concentric coil should have a similar response.

DD coil Pre-amp output scope pictures:
20usec/div.
Top trace is Pre-amp out & 2V/div, shows the full TX cycle and coil ring/decay.
Bottom trace is Integrator output. Note the Voltage level without and with targets.

No target - base line for comparing
Gold ring -
half Dollar -
Eye screw -
Screw driver - Note the Integrator out is nearly saturated and the 1st sample pulse shows.
Screw driver plus Gold ring with GEB added - The GEB lifted the integrator output Voltage off the bottom rail and allows detection of the gold ring.
[ATTACH]41822[/ATTACH]
[ATTACH]41823[/ATTACH]
[ATTACH]41818[/ATTACH]
[ATTACH]41819[/ATTACH]
[ATTACH]41820[/ATTACH]

Decay Voltage during S1 is higher than no target & the zero crossing time during TX on is sooner with the two Steel targets.

Coils
Measured the 25cm mono coil. It is 21 turns, #28 enamel wire, PE Spiral wrap with #28 twisted leads to circuit. 366uH, 3.4 Ohm, 56pF. Sampling can start at 8usec but finding 10-12usec is better.
I am still running Unshielded coils and cables and have not seen noise issues except the Wobbles described in the beginning of this post which is fixed with a PPS rate adjustment. I did try shielding to fix the Wobbles but the shield did nothing. None of the unshielded coil respond to my hand or moving closer to the ground.
This has made me wonder if I have something wrong or is it all the other PI detector circuits/builds have something wrong. Since I getting close to putting coils into shells with epoxy this is making me nervous.
Anyone have thoughts or experience with this?

Also received some coil shells from Don Bowers today.
https://sites.google.com/site/dbcoilshells/home
He lives only 113 miles (182 km) from me. Shells in picture are for: 25cm mono, 25cm DD, 21cm Concentric.

[ATTACH]41815[/ATTACH]

Yes, understand but have been trying the 'three sample' GEB method.
Details are in my thread:

http://www.geotech1.com/forums/showt...ake-on-the-HH2

I would like more detailed discussion of what I have been trying but this isn't the correct thread for that.From another thread

Does this reply describe your latest revision for GEB?

[waltr]

Yes, understand but have been trying the 'three sample' GEB method.
Details are in my thread:

http://www.geotech1.com/forums/showt...ake-on-the-HH2

I would like more detailed discussion of what I have been trying but this isn't the correct thread for that.From another thread

Does this reply describe your latest revision for GEB?

Yes, that is the current GEB scheme I have been using. Have tried some other timings but not as good.
Are you planning on trying this 'three sample' method? I did put a link to the thread that discusses the theory.

[green]

Yes, that is the current GEB scheme I have been using. Have tried some other timings but not as good.
Are you planning on trying this 'three sample' method? I did put a link to the thread that discusses the theory.

http://www.geotech1.com/forums/showt...974#post240974 Shows some target decays.

I think your method is similar to other methods I've seen with GB on adjusted to cancel ground response. With GB off, normally there is a lot more than 20usec between target and EF sample. You would be loosing a lot of the signal with long TC targets with GB off.

Including a picture of control sequence I use. Control sequence is correct, times might be a little different.

[waltr]

This method is from these threads Linked in my post.
http://www.geotech1.com/forums/showt...-Balance/page3
http://www.geotech1.com/forums/showt...Ground-Balance

Your control sequence/timing looks very close to what I am doing.
TX - Delay1(8-35us) - Target sample (15us) - Delay2(20us-yours is 5.4us) - GB sample(15-200us) - then the EFE sample just before the next TX pulse.

With GB off, normally there is a lot more than 20usec between target and EF sample.

I have thought this but haven't seen info on how the timing should change.
Typically timing sequence without GEB is: Delay1 -Target Sample - Delay2 (100-400usec) - EFE sample. This is what I used in the first Code posted which just emulates the hardware timing of the original Hammer Head.

At least with using a microprocessor any timing scheme is pretty easy to do.

[green]

This method is from these threads Linked in my post.
http://www.geotech1.com/forums/showt...-Balance/page3
http://www.geotech1.com/forums/showt...Ground-Balance

Your control sequence/timing looks very close to what I am doing.
TX - Delay1(8-35us) - Target sample (15us) - Delay2(20us-yours is 5.4us) - GB sample(15-200us) - then the EFE sample just before the next TX pulse.


I have thought this but haven't seen info on how the timing should change.
Typically timing sequence without GEB is: Delay1 -Target Sample - Delay2 (100-400usec) - EFE sample. This is what I used in the first Code posted which just emulates the hardware timing of the original Hammer Head.

At least with using a microprocessor any timing scheme is pretty easy to do.

I don't use a micro because I never learned how to program one. I use a minor loop(first delay, target sample, second delay, ground sample). Rate oscillator starts minor loop(EF samples), minor loop ending starts Tx, Tx ending starts minor loop second time(target samples), waits for rate oscillator to start sequence again. Target sample and ground sample control opposite integrator switches the second time through. A switch enables or disables taking a ground sample. Didn't make EF sample, ground- target sample time because I didn't see a easy way with logic chips. Starting the minor loop before Tx makes for maximum time between target samples and EF samples. Would think it would be easy to program sequence in a micro. I've tried making different parts of the minor loop adjustable. Now approximate, first delay(6 to 20usec) and target sample time(9 to 25usec)are pot adjustable, second delay about 4usec, ground sample 100usec, Tx 160usec, rate 1000pps.

[waltr]

We are doing the Same timing sequence- I do the EF sample just before the TX pulse and it is the beginning of the timing sequence.
A big difference is that I run an adjustable GB and EF sample time whereas you seem to have both fixed to 100us plus the target sample.
Whereas I have a Target sample and the No GB sample the same (15us) then as GB adjust is increased the GB sample and EF samples increase by the same amount.
So with GB = 0: EF sample = 0us, TX =100us, Delay1, Sample1 = 15us, delay 2 = 20us, GB sample = 15us.
With GB = 50us: EF = 50us, TX = 100us, delay 1, target sample = 15us, delay 2 = 20us, GB sample = 65us.
This meets the diagram is Post #72 of: http://www.geotech1.com/forums/showt...-Balance/page3

I do have most of the timing adjustable using either a trim pot or panel mounted pot int the processor's ADCs.
Either way, hardware timing or software timing we accomplish the same thing.

Have you been able to Test the GB on mineralized soil? I haven't as yet so do not know if this GB scheme actually works.
Have you tried slightly different timing, delays & samples, and tested on mineralized ground?

The one thing I have found is with the GB sampling there becomes a 'pivot point' where high conductors cause a negative output from the integrator and low conductors give a positive output.
Other variations of timing does not do this.

[Qiaozhi]

We are doing the Same timing sequence- I do the EF sample just before the TX pulse and it is the beginning of the timing sequence.
A big difference is that I run an adjustable GB and EF sample time whereas you seem to have both fixed to 100us plus the target sample.
Whereas I have a Target sample and the No GB sample the same (15us) then as GB adjust is increased the GB sample and EF samples increase by the same amount.
So with GB = 0: EF sample = 0us, TX =100us, Delay1, Sample1 = 15us, delay 2 = 20us, GB sample = 15us.
With GB = 50us: EF = 50us, TX = 100us, delay 1, target sample = 15us, delay 2 = 20us, GB sample = 65us.
This meets the diagram is Post #72 of: http://www.geotech1.com/forums/showt...-Balance/page3

I do have most of the timing adjustable using either a trim pot or panel mounted pot int the processor's ADCs.
Either way, hardware timing or software timing we accomplish the same thing.

Have you been able to Test the GB on mineralized soil? I haven't as yet so do not know if this GB scheme actually works.
Have you tried slightly different timing, delays & samples, and tested on mineralized ground?

The one thing I have found is with the GB sampling there becomes a 'pivot point' where high conductors cause a negative output from the integrator and low conductors give a positive output.
Other variations of timing does not do this.

I'm not sure I follow your timing scheme, but these posts might be of interest ->
http://www.geotech1.com/forums/showt...548#post229548
http://www.geotech1.com/forums/showt...769#post201769
http://www.geotech1.com/forums/showt...761#post182761
http://www.geotech1.com/forums/showt...718#post208718