Hammerhead Works but not detecting Deep. Help please.

[Lucas Kazuaki]

So i built the hammerhead Following the procedures on the PDF provided in Geotech1.
It works!!!!!
I can find coins, pulltabs and more. The only problem is that i can only find those objects at around 10cm and i have seen people finding objects at around 25 or even 35cm. I have tried to play with the pulse width and even changed the resistors to be able to have long pulses but i usually tested the circuit with pulses at around 50us to 100us, changing the frequency from around 615hz to 1500hz, playing with the delay time from 10us to around 60us, sample width at around 20us to 35us.
i even tried changing the resistor on the first amplifier. that is suggested to reduce the gain (2k resistor instead of 1k).
All of those settings did change the depth of detection, and even gave me better results but not as good as i seen on the forums.
Ok now lets go to the coils which i belive is one of the most important parts because if they fail, even the best circuit will not give anything. So i tried coils from 20cm to 35cm all of them worked but like i said the same depth was achived with any coil. i used enamel wire that i bought from a transformer factory and i have tried many different gauges of wire. from a thicker 24awg to even 30awg. I tested their inductances (from 300uH to 500uH). I have read another PDF about "fast coil" and even created a shield following the indication to Not complete the loop around the coil and short the shield. i am also using coax cable used from radio comms/ television its a white cable with a solid core of copper and a braid around it.
so i wanted to see if anyone still working on that project could help me. Ah i almost forgot, yes i did remore the components needed to calibrate the op amps (exacly like the procedure explained in the PDF).
sorry if my english isnt good enough, please ask me questions so i can try to explain a little better if needed.

Any help will be appreciated.

[Qiaozhi]

Have you correctly adjusted the damping resistor?

[Emiliano_070]

Hello, here comes the million dollar question. How to calculate the value of the adequate resistance for each coil. Is there a formula for the calculation or is it necessary an oscilloscope.Thank you

[Wahyu]

for best result use oscilloscope, adjust delay and R damping

[kt315]

Have you correctly adjusted the damping resistor?

have you correctly choiced the dumbs' first desk book to read before asking the questions?

http://www.geotech1.com/forums/forum...Published-2015

[Qiaozhi]

Hello, here comes the million dollar question. How to calculate the value of the adequate resistance for each coil. Is there a formula for the calculation or is it necessary an oscilloscope.Thank you

http://www.geotech1.com/forums/showt...520#post236520

Personally I wouldn't even attempt to build the Hammerhead project without an oscilloscope.

[Lucas Kazuaki]

Yes I did. I choose the best value that is around 470ohms by testing each value until the decay was the most critical possible.
what i just did and it increased the depth a bit was to change my coil cable instead of using a expansive and great coax cable i am using now the most cheap cable. Actually it looks like a guitar cable (wire inside with a braid around). but it is still pretty far from 20 or 30cm depth for coins, pulltabs etc.

[waltr]

The cable can really increase the total C for the coil.
Did you re-evaluate the Dumping R value after changing the cable?
Using a pot to adjust dumping R works well to find the optimum value.

Is coil Shielded? and how?

[Lucas Kazuaki]

The cable can really increase the total C for the coil.
Did you re-evaluate the Dumping R value after changing the cable?
Using a pot to adjust dumping R works well to find the optimum value.

Is coil Shielded? and how?

Hello,
I did change the resistors and used my scope to keep them as precise as i could.
The cables do change the total C but it isnt that much as i made it really short and i keep checking the decay to confirm any changes in capacitance.
How could i use a Pot to adjust dumping R? I tried using a resistor in paralel with another resistor but this second one in series with the pot but even using this configuration the pot got smelly and burned. Thats too much power to be dissipated on a small pot
The coil is sure shielded. I wrapped the coil with those spirals made of plastic (2 layers) used as spacers to cover with aluminium foil. I know its not the best but i didnt find any mesh or braid like materials to be used. After using the shield the circuit became more stable and from what i see on the decay wave it didnt change C a lot.

[6666]

did you leave a gap in the aluminium foil, most important
foil can reduce sensitivity , you can make another coil without foil to test the difference

[Lucas Kazuaki]

did you leave a gap in the aluminium foil, most important
foil can reduce sensitivity , you can make another coil without foil to test the difference

yes i did leave a gap.
i have 7 coils made with different diameters and wire gauges. with and without shielding. all have similar results. using cable or connected direcly to the circuit.

If anyone here need some pictures of the waves on my scope i can try posting it.

[6666]

what version HH did you make ? when you built it did you test the value of the resistors in the preamp part of the circuit before soldering them
did you try changeing the preamp IC, or any others

[Lucas Kazuaki]

what version HH did you make ? when you built it did you test the value of the resistors in the preamp part of the circuit before soldering them

It is the version that is on the projects part Probably the first one. i didnt test them but what i did like i said was to use a 2k resistor in place of the 1k resistor to reduce the gain a bit as some have suggested

[waltr]

Hello,
I did change the resistors and used my scope to keep them as precise as i could.
The cables do change the total C but it isnt that much as i made it really short and i keep checking the decay to confirm any changes in capacitance.
How could i use a Pot to adjust dumping R? I tried using a resistor in paralel with another resistor but this second one in series with the pot but even using this configuration the pot got smelly and burned. Thats too much power to be dissipated on a small pot=

Use a small pot in Parallel and series with other resistors. Example:
Put a 1 or 2k fixed 1/2W resistor across coil (primary dumping R) then a 5k pot in series with 100-330 Ohm resistor- this is then put across the 1/2W resistor and is adjusted for critical damping.Remove Pot/series and measure the resistance of the combination to find the optimal value that goes in parallel with primary R.

Circuit in this thread: http://www.geotech1.com/forums/showt...aming-resistor

Are you measuring the damping at the Coil out or the pre-amp out?

You may want to try an un-shielded coil to see if the shield is the problem as 6666 suggests.

Another area of the circuit that is critical in the integrator stage. Ensure the 100nF caps are good quality. Next is to ensure the first and second Samples are far enough apart, at least 35usec and up to 100usec (remember that the second sample subtracts from the first).

Is the Coil Current leveling before reaching a peak?
Measure the Pulse ON waveform across the 1 Ohm MOSFET series R without the 1000uF cap.
With short pulses this will ramp up (looking like a triangle) to a peak (Ohms law and R value give the coil current).
With longer pulses the Voltage should level out indicating the coil current is near maximum.
Some experiments I and others have done show that having the coil current level out even with a lower peak coil current improves sensitivity (distance).
This to an effect of the Coil Tau (L/R) and adding a little series R to the coil. This allows the Coil current to level out in a shorter pulse.

Last- The Soil can have a great effect of detection depth so hard to compare to other's results.

[waltr]

Is the Threshold low enough?
Should be adjusted so there is slight 'chatter' or tone.