My take on the HH2

[waltr]

I think Davor's equation predicts end of sample would be 100 which means ground sample is 50usec. Works if ground slope is -1 and EF sample is zero. With ground slope =-1.25 which I get with 100usec constant current Tx, ground sample needs to be around 100usec.

Duh.. you're right. d is END of GB sample not GB sample time.

[waltr]

More on GEB
To clarify the Timing I am using attached are scope captures. Top trace feeds the inverting Integrator, bottom trace feeds to non-inverting integrator input. The scope uses External trigger at the end of the TX pulse so traces start at end of TX pulse.
First scope capture of the sample timing with GEB = 0. This is D1 = 15us, S1 = 15us, D2 =15us, S2 = 15us. S3 is a very small, ~1us before the TX.
Second is with GEB set to 100us. D1, S1, D2 all still 15us but S2 = 115us and S3 = 100us.



Obtained a bag of mineralized soil from a kind forum member to test GEB. With the GEB set to 0, this 'hot soil' causes a response from the detector. Graph 'dirt' is the Voltage change out of Integrator when the hot soil is placed on coil verse GEB values. Note NO Response with GEB set to 100usec and response going negative when GEB is greater than 100usec.



Next test is to compare the response to targets without and with the 'hot soil' between coil and target.
Table and graph is Voltage change at Integrator output for a few common targets. Targets are 1.5 " (3.8cm) above coil. This shows a slight loss of depth with about 1" (2.5cm) of hot dirt between target and coil. A bit odd but with the mono coil the 'high' conductive targets response are a little greater with the hot soil on the coil but the opposite for the 'low' conductive targets- one explanation is I did not get the GEB control to the Exact same position for the two measurements with the mono coil. I would expect a slight decrease of depth detected is soil verse air.

GEB = 100		Concentric 8"		Mono 10"
		Air	Dirt	Air	Dirt
Ag coin	2	-1.15	-1.06	-0.77	-0.84
Ag Dime	3	-1.60	-1.62	-0.84	-0.92
Ag Quarter	4	-2.98	-2.89	-1.49	-1.58
Cu penny	5	-1.95	-1.92	-0.97	-1.04
slug	6	0.92	0.66	0.64	0.35
nickel	7	3.95	3.00	2.08	1.71

[green]

More on GEB
To clarify the Timing I am using attached are scope captures. Top trace feeds the inverting Integrator, bottom trace feeds to non-inverting integrator input. The scope uses External trigger at the end of the TX pulse so traces start at end of TX pulse.
First scope capture of the sample timing with GEB = 0. This is D1 = 15us, S1 = 15us, D2 =15us, S2 = 15us. S3 is a very small, ~1us before the TX.
Second is with GEB set to 100us. D1, S1, D2 all still 15us but S2 = 115us and S3 = 100us.
[ATTACH]42526[/ATTACH]
[ATTACH]42527[/ATTACH]

Obtained a bag of mineralized soil from a kind forum member to test GEB. With the GEB set to 0, this 'hot soil' causes a response from the detector. Graph 'dirt' is the Voltage change out of Integrator when the hot soil is placed on coil verse GEB values. Note NO Response with GEB set to 100usec and response going negative when GEB is greater than 100usec.

[ATTACH]42528[/ATTACH]

Next test is to compare the response to targets without and with the 'hot soil' between coil and target.
Table and graph is Voltage change at Integrator output for a few common targets. Targets are 1.5 " (3.8cm) above coil. This shows a slight loss of depth with about 1" (2.5cm) of hot dirt between target and coil. A bit odd but with the mono coil the 'high' conductive targets response are a little greater with the hot soil on the coil but the opposite for the 'low' conductive targets- one explanation is I did not get the GEB control to the Exact same position for the two measurements with the mono coil. I would expect a slight decrease of depth detected is soil verse air.

GEB = 100		Concentric 8"		Mono 10"
		Air	Dirt	Air	Dirt
Ag coin	2	-1.15	-1.06	-0.77	-0.84
Ag Dime	3	-1.60	-1.62	-0.84	-0.92
Ag Quarter	4	-2.98	-2.89	-1.49	-1.58
Cu penny	5	-1.95	-1.92	-0.97	-1.04
slug	6	0.92	0.66	0.64	0.35
nickel	7	3.95	3.00	2.08	1.71

[ATTACH]42529[/ATTACH]

Most of the time when I measure integrator out change with GEB on, I first adjust GB so there is no change in integrator out when I place the bag on the coil or take it off, then make the target measurement with the bag off since it is easier for me to get repeatability when charting target distance vs amplitude. I have done like you did at one distance by building a bridge over the coil where the bag would go under the bridge and testing with and with out the bag. I didn't see a difference. Not saying there shouldn't be. A lot of your targets didn't show much difference except for the slug. What is the slug and any guess why it would test that much different with and without the dirt?

[waltr]

Most of the time when I measure integrator out change with GEB on, I first adjust GB so there is no change in integrator out when I place the bag on the coil or take it off, then make the target measurement with the bag off since it is easier for me to get repeatability when charting target distance vs amplitude. I have done like you did at one distance by building a bridge over the coil where the bag would go under the bridge and testing with and with out the bag. I didn't see a difference. Not saying there shouldn't be. A lot of your targets didn't show much difference except for the slug. What is the slug and any guess why it would test that much different with and without the dirt?

I thought I had Adjusted GEB for zero change with the hot soil but may have not gotten it perfect between those two sets of measurements.
I did build a bridge across the coil and put the hot soil under the bridge. This keeps the target distance the same.
I wanted to measure IF the hot soil changed target response verse response with Air.

The 'Slug' is a zinc plated steel punch-out from an electrical junction box. I have been using it since it is 'coin' size and is steel (iron).
Actually the Nickel also has a decease with the hot soil also. Only thing common with these two targets are they Both give a Positive response, even when GEB is 0 or 100.
All the other targets give a positive response with GEB = 0 and a Negative response when GEB = 100. Need to check this with other targets that give Positive response when GEB = 100.

Another interesting response is a new steel nail verse the same size nail but very rusty. The new nail give a positive the Rusty nail negative. Been digging a lot of very rusty nails out of my yard. They were sounding with a low/high tones so sounds like Dime, quarter, penny and not like steel which is high/low tones.

Here is a graph of the target response at verse GEB setting. Target numbers same as above with the addition of the Hot soil as Target #1.

[waltr]

I built a pin pointer using Teemos' circuit.
http://www.geotech1.com/forums/showt...tector-project
Pin pointer details and pictures in this post:
http://www.geotech1.com/forums/showt...483#post241483

[waltr]

re-do of mods
The Mods in Post #70 were not the best. At first it seemed the sensitivity was still good but it was not.
I put the Gain stages after the JFET switches back in and then decreased the gain in the SAT stage (external pot). I found that in electrically noise areas the SAT gain needs to be lower but can be increased in electrically quite places.

The HH originally runs a fixed Gain in the SAT op-amp of 101. I added an external pot to adjust gain from 16 to 216 (R37 in my schematics, sheet 2 in post #1). When the gain is high then the SAT output runs more like a comparator output- zero with no target - or hitting the op-amp rails (full negative or positive Voltage) when a target is detected. This then created audio tones of either Full high or full low. With lower SAT gain the output is more proportional to the target signal strength and the audio tones have the full range of frequencies.

Discrimination
Another addition is a meter on the Integrator output. This helps to determine target signal strength and for pin-pointing since the integrator output is Non-motion. I used an old VU meter with 500uA full scale. It is connecting from -5V and through a 20k series resistor to the Integrator output, -5V to +5V. This sets the meter to mid-scale with no target (5V/250uA = 20k). Then it goes to the left for high conductive targets (dimes, quarters) and to the right for low conductive targets (nickels) when the GEB is adjusted for 50-150usec - see posts above on target response with GEB adjustments.

The combination of GEB giving Negative or Positive outputs and Tone plus the meter allows some discrimination of targets. I have been detecting a lot in my yard where there are lots of rusty nails but a few other objects. A ferrous target tends to not give much Voltage response (see previous posts) with GEB set near 100usec - this is the response 'hole'. Whereas coins, aluminum, etc give a larger Voltage response. I now can tell a rusty nail from other objects by the tones and the meter (of course the target size, shape and depth effects the response) most of the time. Nickel and Pull-tab gives a high tone with a larger Voltage (meter movement to the right). Dimes, Quarters & pennies (clad & silver) gives a Low tone and meter movement to the left. Iron can give a high or low tone quickly followed by the other tone but a very small meter movement. Even larger ferrous targets do not move the meter much and long objects like nails will give a double low/high when moving the coil along the nail's length. This is not to be confused when two smaller target are near each other as when I found two dimes a few inches apart. I was pretty sure is was not a nail since the low/high tones were crisper and meter moved more than nails tend to do but there was a double set of tones like a nail gives.
This is not the discrimination found on VLF detectors but much more than the basic PI detector.

The PIC1501 VCO work well. The HH Threshold is now not needed (SAT output offset should be fixed to near Zero Volts) since the PIC VCO code sets threshold 'center' on boot-up and the threshold 'range' (high or lower then center) is set with a Pot into an PIC 1501 ADC.

[Tim]

Great stuff waltr. I like the meter addition. Down at Dads last week I took the Baracuda out on the side block. Usually I have ran it with shortest delay (possible with coil), but for this site I experimented, raising delay until a rusty 2" nail was stuttery. Yes, basically a discrimination suitable for this particular situation.
I really like your enthusiasm and where you are going with this. You are very adept.

[waltr]

Great stuff waltr. I like the meter addition. Down at Dads last week I took the Baracuda out on the side block. Usually I have ran it with shortest delay (possible with coil), but for this site I experimented, raising delay until a rusty 2" nail was stuttery. Yes, basically a discrimination suitable for this particular situation.
I really like your enthusiasm and where you are going with this. You are very adept.

Thanks.
I like the idea of changing the Delay to help discriminate.
I need to play with doing that since I also run with nearly the shortest delay (possible with the coil I'm using).

[waltr]

Update
I have not posted for a while since I have been out using this detector finding things.
One upgrade was replacing the old corded headphones with aptX Low Latence BlueTooth head phones. It is now great not having a cord to get caught on brush etc. I bought the Trond Transmitter/Reciever and the Wireless headphones.
https://www.amazon.com/TROND-Bluetoo...CBNWEGDKAMN09B
https://www.amazon.com/TROND-Bluetoo...A0ZV3EJ9T2YX0E
I attached the BT Tx to the detector case with double sided foam tape and made a Mono to Stereo cable to plug into the Detector's audio out. Great sound and I just wear the headphones around my neck so I can still hear things around me. See photo.

I have been mostly detecting at old farm steads that existed in 1857 (on old maps) but gone by 1971 and a few parks and once at the beach.
The old farms have lots and lots of old rusty iron but a few interesting objects. Discriminating small iron objects is impossible - the signal, tone plus meter (see post #81 about meter), can easily be a coin at depth which has made coin finds a nice surprise (see next post on finds). Any small object pin-points with the 8" concentric coil with silver/copper giving a Negative meter (and Low tone) and nickel, brass, aluminum giving positive meter (high tone). Iron if small tend to be a positive meter.
Pos/Neg meter and High/Low tones only possible with GEB set greater than 50usec. Best is with GEB set to 100usec which is my default. Delay setting with Concentric coil is 12usec, this gives best sensitivity.
Nails and other long iron objects can give positive or negative readings. This depends on the object orientation- Horizontal nails can give a negative then positive then negative readings when sweeping the coil in-line with the length of the nail. Large nails/wire can also sound like two targets. Larger iron object also do this but with much greater meter movement. Very large iron can saturate the integrator stage (where meter connects) moving the meter to Full scale - negative/positive when sweeping coil. This is one way to determine object is large iron. The other way to determine large iron is sweeping a grid in two or more directions to "map" the shape. When the object is greater than a foot (30cm) then not worth digging. I have dug a small area on some just to confirm the object is huge.
Increasing the Sampling Delay is not totally reliable to determine if iron or not. Many medium /small iron objects go away with increased Delay. I still need to try this more.
An aluminum drink can gives a strong signal but always positive only. Same with pull-tabs.
My wife and I went to the Jersey Shore for a day just to see the ocean and spend time before the crowds. Spent a little time detecting on the beach using a 10.5" Mono coil while my wife looked for shells. The wet sand in itself wasn't a problem but if I bumped the coil onto the wet sand it Falsed. Did bury a penny and it was detected easily so detector seemed to work correctly. Didn't find much as the beach was very clean and also saw 'scoop' marks from other detectorist.
Since beach detecting is a secondary use and may do this twice a year I don't plan on working out why bumping the wet sand gave a false signal. Also being my detector is not water proof although coil is, and the water was very cold so I did not detect in the water.
In conclusion this is still a Dig Everything detector as iron objects can give any reading/tone.

[6666]

Increasing the Sampling Delay is not totally reliable to determine if iron or not

Its only an indicator, thanks for update on your machine.

[Tim]

Yes, thanks for the update waltr. Seems you have comperehensively tested it and achieved a practical result. Without searching for the Holy Grail, this is all we can expect to achieve.

[waltr]

Thanks 6666 & Tim.

I do like this detector as it is quite sensitive. I am writing up a Finds post so stay tuned.
In two weeks I will be with a dozen other detectorist at a 1700/1800 farm in south Jersey. It will be my first time around other detectors so will be interesting making some comparisons.

I still have the idea of measuring Phase during TX pulse on with IB coils for Fe detection. This will be next winter's project.

[waltr]

I have a find thread on the Friendly Metal Detecting forum. Rather than post all that here I think its better just to post a link. No registration is need to view pictures on this forum.
Enjoy.
https://metaldetectingforum.com/showthread.php?t=262517

There is a link in that thread to a coin thread but here is the link to my first 1800's coin find.
https://metaldetectingforum.com/showthread.php?t=262735

[Aldere42]

I have a find thread on the Friendly Metal Detecting forum. Rather than post all that here I think its better just to post a link. No registration is need to view pictures on this forum.
Enjoy.
https://metaldetectingforum.com/showthread.php?t=262517

There is a link in that thread to a coin thread but here is the link to my first 1800's coin find.
https://metaldetectingforum.com/showthread.php?t=262735

Timing and the PIC

I used a PIC16F88 since I have these and they have ADC input pins. Running a 20MHz ceramic resonator for a 200nsec instruction cycle.
TMR0 interrupts every 426usec and in the ISR the pulse/sampling sequence takes place. This is just like Carl's C code example. There is a TMR0 'tick flag' set.
In the MAIN() code section after all initialization is done there is a ' main _loop'. This watches the 'tick flag' and increments a counter. The counter is used for a crude 'state machine' to sequence reading the ADCs. This action obtain all ADCs 29 times a second which is plenty fast for manually turning a pot.
The five ADC inputs are connected to 5k Ohm 15 turn trim pots and allow adjustment of the following:
ADC0 - not used in this code but open for GEB or for direct sampling.
ADC1- first sample Delay time. This is a panel mounted pot
ADC2- TX pulse width
ADC3- Sample time
ADC4- second sample delay time
The ADC values are scaled and then added to the minimum time for TRM2.
TMR2 is setup with these 'values' for each of the times in the sequence.
This version of code is simply: TX pulse, delay1, sample1, delay2, sample2.
There is optional code here that I put in almost all PIC projects. These are an interrupt driven TX & RX UARTs with FIFO (ring buffers). This is handy for 'real time' debugging and was used to output ADC reading and the calculated times. There are a couple of "#define " (debug1 & serial) statements used to enable/disable building code.
There is the possibility of output info on the UART to an LCD display on future versions.
As Carl and others have stated- there are lots of possibilities for experimentation when using a processor. I setup trim pots to easily adjust all the timing so could try nd measure what works.
Currently with the 12" DD coil the timings are:
100us TX (with a 10 Ohm series R to coil), 8-15us delay1, 15us samples & 34us delay2.
I may just hard code the TX pulse, Sample time and delay2 time in the future to open up ADCs for other uses.



Schematic and the PIC assembler code (unzip and change extension from .txt to .asm)

[ATTACH]41477[/ATTACH]
[ATTACH]41478[/ATTACH]

hello my masters in this forum I'm new this is the shared part of the circuit you have 16F88 pcb drawing and you can send all documents from my gmail address.
Thank you

[Aldere42]

[email protected]