My take on the HH2

[Chiv]

just finished making a sniper coil running @239.1uh 3.6ohms with out cable and nulled with 60ohm which slightly under nulled for best response to gold ring, no hand movement gave a signal at all.
Added cable type wb1510 mic type of 1.5m long change a few things 315uh 149.8pf 6.5ohm nulled with 55ohm for good null I still get no type of sig from hand movement, this coil has given me the best response to rings and small bean type sinkers to date hitting 15cm in air test for rings and 25mm squares ally heat sink when adjusted right 26cm good sig and 29cm very faint sig
the one closest to the logo on mat is the best one I built so far, just trying all sorts of winding patterns to see what works the best, the heaver coil really good for iron and ally type of things but struggle on rings and bean sinker.
Have been playing around with your resister in line (helpful hint you gave me) with different coils too and found depending on coils make up 2ohm good for emi filter - 8 to 10 ohm gives a real good clean scope pattern but inductance changes a fair bit. So might have to make a coil with high ohm reading to counter balance the resister inline.

[Tim]

Chiv this basket weave style may be worth a try for your experimenting. It is documented here somewhere. Very easy to make on a plastic-coated cardboard(or similar) form. Simply cut an odd number of slots at even intervals. Use thinner wire to increase resistance if necessary, depending on the R requirements of your detector. Not sure of the capacitive effect this will have, or damping requirements, though.
Very skillful coil winding there Chiv.

[waltr]

Great stuff waltr. Very comprehensive, and all too technical for me (yet). Small natural gold and heavy mineralisation will be my main concerns for fiddling with the HH. Yes, that damned mains electricity is a problem. My last residence had only minimal interference in close proximity to the fuse box, but where I am now (single story unit block) all the wires run through my roof, and there is a distributor across the road.
Awaiting my Crazy-tech coil molds for the IDXpro and IGSL Musky, but still pre-occupied with a simple BFO and an IB....
Keep up the good work.

I still do not understand every thing posted in threads here but do read and then experiment.
This is what I am trying to do in this thread- relate the results of the experiments.

just finished making a sniper coil running @239.1uh 3.6ohms with out cable and nulled with 60ohm which slightly under nulled for best response to gold ring, no hand movement gave a signal at all.
Added cable type wb1510 mic type of 1.5m long change a few things 315uh 149.8pf 6.5ohm nulled with 55ohm for good null I still get no type of sig from hand movement, this coil has given me the best response to rings and small bean type sinkers to date hitting 15cm in air test for rings and 25mm squares ally heat sink when adjusted right 26cm good sig and 29cm very faint sig
[ATTACH]41831[/ATTACH] the one closest to the logo on mat is the best one I built so far, just trying all sorts of winding patterns to see what works the best, the heaver coil really good for iron and ally type of things but struggle on rings and bean sinker.
Have been playing around with your resister in line (helpful hint you gave me) with different coils too and found depending on coils make up 2ohm good for emi filter - 8 to 10 ohm gives a real good clean scope pattern but inductance changes a fair bit. So might have to make a coil with high ohm reading to counter balance the resister inline.

Some of what you are saying does not make sense (maybe it is a translation thing).

The total series resistance with the coil will not change the coil inductance. What is does is allow the coil's magnetic field to reach maximum as seen in the current through the coil/series R. This is the coils charging Tau which equals inductance divided by resistance (Tau = L/R). It does not matter where the resistance is, in the coil wire or as a resistor added in series with the coil, it is the TOTAL series resistance that determines the charging Tau.

nulled with 60ohm

Do you mean to critically Damping the coil? As in the resistor across the coil?
If so 60 Ohm is a very low value. Typical PI coils damp with a resistor in the range of 300 to 1000 Ohm.
The value is mainly dependent on the Capacitance of the coil including coil and leads to the shield.
Are you sure of this value R?
You also really need to use an O'scope to see the coil ringing and adjust the Damping R value. And a value TOO low will cause the received signal to extend.

[waltr]

I asked the Coil shield or not shield in the Coils forum here:
http://www.geotech1.com/forums/showt...-or-Unshielded

Posting this link to complete the referencing of threads.

[Chiv]

sorry Waltr yes Damping was the word I should of used and yes that coil was 60ohms, most of my other coils witch are a lot bigger where in the range of 380 to 650ohms to Critical damping.
Been thinking inductance went up in coil is because I put the resister in coil head not on the board, I did not think about that until reading your post or it could be the tool I'm using to measure the inductance

[waltr]

sorry Waltr yes Damping was the word I should of used and yes that coil was 60ohms, most of my other coils witch are a lot bigger where in the range of 380 to 650ohms to Critical damping.
Been thinking inductance went up in coil is because I put the resister in coil head not on the board, I did not think about that until reading your post or it could be the tool I'm using to measure the inductance

Ok, makes a more sense.
Measuring inductance can be hard if not using the right tools and have the right setup. Also, other factors can influence the measurement.

Are you saying that the Coil Resistance is 60 Ohm? or you added a 60 Ohm resistor to dampen the coil?
The former seems too large and the latter too small.

Look at the pre-amp output with a scope and then adjust the damping R. I start with a 1k Ohm R and then use the POT/R combination in parallel to find the critical damping. This is NO ringing and the shortest decay (Too low of a damping R will cause a much longer recovery on the pre-amp output).
Remove the Pot/R and measure. Then insert that value into the circuit and recheck pre-amp out with scope.

Never tried putting the damping R in the coil head. One reason this may not be a good idea is that the R will be in the coil's magnetic field and respond like a target.
You can put stuff at the coil on a VLF detector but not a PI detector. The recommend place for the damping R is on the PCB or in the Coils cable connector at the pcb/box.

[Chiv]

Hi Waltr yes do use a scope and the coil is 3.5ohm it self and I used trim pot tool(had to make a smaller R tool for these smaller coils) for finding best damping resistance which come out to 60ohm, my take(after reading on the forum) on putting any thing in the search head was ok in a pi as long as it is fixed and dose not move with in the windings. think I,m leading you away from what you thread is all about with this sorry about that. I post more on my barra thread as I'm just about finished putting 3d printer together to make some templates up for other different coil wind ups

[6666]

Am working on replacing the three op-amps and VCO chip with an 8-pin PIC (I'll post details once have this working).

Thats interesting thanks

[waltr]

Coils, GEB and Target ID
Experimenting with output response and different coils, settings.
I placed each target 1.5 inch (3.8cm) above the coil center and measured to Integrator output with a DVM. I subtracted the No Target Voltage from the Target Voltage to get the Difference. Delay Set to 15usec. Coils are: 10" Mono, 13" DD (Pictures in above posts) and an 8" concentric (Details on this coil coming).
Target list (number correspond to numbers on Chart.

1	No Target
2	Ag dime
3	Ag half
4	Cu penny
5	Clad dime
6	Clad quarter
7	sm Alum
8	Nickle
9	Gold ring
10	eye screw
11	Brass key
12	lg Alum
13	Nail
14	ferrite (chart 1) or Alum coin (chart 2)

First chart with GEB = 0usec. Note that Only the Steel eye screw and the Nail gave a Negative response and only on the DD coil.


In the second chart the GEB is set to 50usec then to 25usec (only on Concentric coil). The big difference is more targets give a Negative response. This would be helpful to ID target types with a High/Low, Low/High (Dual) tone audio (still working on this 6666). Also, adjustment of GEB could be used for Target ID.

[waltr]

PIC Dual tone VCO
As promised here is code for a PIC12F1501 to do a Dual Tone VCO with an adjustable +/- Threshold.
VCO-12F1501.zip

This 8 pin PIC has an NCO (numerically controlled oscillator) module which makes producing Audio tones very easy. The NCO has a 24 bit 'count' to produce frequencies from 15Hz to over 500kHz using the Internal 16MHz oscillator. For audio I only use the lowest 8 bits of the NCO for tones from 15Hz to 1945Hz.

This does the same thing as this the circuit posted by mickstv (I did prototype this circuit and it works very well):
http://www.geotech1.com/forums/showt...502#post218502
This sends the SAT output to a VCO chip (CD4046) and also full wave rectifies the SAT signal with an adjustable Threshold.

The PIC code I wrote first delays (2 seconds) then samples the level of the SAT output. This becomes the SAT Center value (value expected with No target) around which the Threshold is set. This is needed since changing Coils, Delay, Gain, threshold (HH circuit) and/or GEB settings changes the No Target SAT output Voltage.
There is an input that when grounded causes the SAT Zero calibration to be performed. So if the SAT Voltage level changes one can either Power cycle the detector or push a NO button to perform a auto-cal of the SAT level. The unused inputs have internal weak pull-ups enabled so no external pull-ups required.
When the SAT signal goes higher than the Center + threshold, the Tone (audio output) is turned on and the Tone frequency increases with high SAT signal level. The opposite happens when the SAT signal goes lower than Center - threshold. The tone is turned on and the tone frequency decreases with lower SAT signal level. When the SAT Voltage level is within the threshold the audio is quiet.
This in conjunction with an IB coils and/or GEB pulses will give a High/Low tones for Gold, copper and Low/high tones for Silver. See my post above about Integrator output levels with different targets and GEB settings.

I had tried to do the Level to tone with a 12F675 PIC but ran into Interrupt over runs which blocked reading the ADC to get the SAT Voltage level. This was using a Timer interrupt to time the half-cycles of the audio tone. This PIC only has a 4MHz internal oscillator so the math needed took too long at higher audio tones. I did start over using this PIC so maybe I can write better code this time around. If I can get this to work then I'll post the code.

Last is to connect the PIC VCO to the HH circuits. First issue to how to power the PIC. After careful study and experiments (I did miss-connect once and killed the PIC, a 78L05 and a MCP604 op-amp). The simplest way to Power is connect the PIC between the 'ground' (which is Battery Plus) and the -5VD regulator (79L05). This puts the PICs VDD at the Zero Voltage level of the op-amps (examine my schematics posted in above posts). Since the SAT output goes +5 to -5 a simple 2:1 resistor Voltage divider works to put the SAT output at 0-5V referenced to the PIC's Vss (-5 to 0V referenced to the op-amp ground). The PIC ADC wants a maximum of 2.5k Ohm input source so 5k or 4.7k resistors are perfect to drive the ADC input.
The Audio out of the PIC can be connected to the RC filter that the 555 drives. My schematic has a selection jumper to allow feeding the audio output stage with a different audio source.

The PIC SAT input is simply a jumper from the SAT out op-amp. Direct connection is fine but a few hundred Ohms to a 1k Ohm series resistor would allow the PIC's protection diodes to work (prevent killing the PIC's ADC input if the SAT output Voltage exceeds to PIC's Vdd or Vss).
So, 1-PIC12F1501, a 100nF cap, a 5k pot, a NO push button switch, 2- 4.7k and a 1k adds a Dual tone VCO to a HH detector.
See the source code for PIC pin out functions.

[waltr]

Additional info on PIC Dual tone VCO
There is an output that turns an LED on when Signal is higher than SAT zero and off when lower. I did this as a debugging aide. this could be connected to additional circuit to turn on say a Green LED when signal high and a yellow LED when signal low.
Also an unused input that could be used as a 'mode' selection or reverse the Tones or something else.
Maybe an Fe input from Phase info (future project option in the main PIC) that could modulate the Tone..
Also should have a 5-pin header for connection to a PICKit3 to Flash code.
This PIC also has a PWM module that could be PWM'ed, increase duty cycle on higher signal, to drive a meter on other indicator.
This PIC with the NCO still has lots of instruction cycle time and space for added features. Suggestions of features to add are welcome.

[Tim]

This is great progress waltr. I, for one, really appreciate you posting this. Although I have the Pickit3 ( I bought to do the Pickini project) I haven't got there yet, nor to the HHrevD, so I cannot yet suggest added features As previously indicated my direction is small gold, so the high/low is very good. Can the SAT be adjustable?. Does this option lend itself to a centred meter? For another option I have some LM3914 LED drivers with the intent of a meter alternative.
Thank you waltr.

[waltr]

The SAT circuit is the same as the original HH, cap coupled op-amp with an adjustment pot to set the TC of the SAT circuit. I currently have this on a trim pot and not on an external pot.
Check the schematics I posted. The HH Sat circuit does the same thing as the first op-amp in mickstv's VCO circuit.

[6666]

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

[6666]

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

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.