Hammerhead project - need help

[Nick]

Hi All,

I am building this project and I run into a trouble. I am using RevC21 and through-hole PCB Layout. I was following the instructions from the document located here http://www.thunting.com/geotech/pages/metdet/projects/pi1/pi1_300c.pdf

The first issue is that using R18 I can't adjust the voltage in TP4 to be between -4V and +4V (see page 9). It goes between -0.6V and +2V. How can I fix this? Also adjusting the R23 does not seem to make any difference. I went ahead and build the rest of the project. When powered up the speaker produces a tone that can be adjusted by R2, but no mather what I do, I can't get to silence it. Note, I don't have a coil attached at this time.

In addition I am not sure where I have to connect the gate for Q3, to the collector of Q2, or between R8 and R9? Also what is the shortcut between the base of Q11 and pin 7 of IC9 used for? And one last question regarding R30 and R32. In the older version those are listed as 39K, when in the revision C1 from Jan 28, R30 is 150K and R32 is 100K (shouldn't they be the same value?)

Thanks for your help.

Nick

p.s. I am including photo of the assembled project

[Carl-NC]

Re: Hammerhead project - need help

Nick,

While the text of the document is (mostly) still valid, you should be building off the newer schematics posted on the Hammerhead page. There are 2 options, both of which have R7 & R8 shorted. Opt 2 bypasses the 555 VCO stage via the "shortcut", it is otherwise left open.

I believe I skewed R30 & R32 differently because most of the adjustment needed for the threshold is on the negative side.

--Carl

[Nick]

Re: Hammerhead project - need help

Hi Carl,

Thanks for the quick response. There are three schematics currently available. I build my project according to the "Full schematic & placement (PDF-509K) - Rev C1 -- 28 Jan 2004" document located here http://www.thunting.com/geotech/pages/metdet/projects/hammerhead/HHc1.pdf

In this option the R7 and R8 exist. I have R22 shortened and C16 ommitted, and that is the only difference from your diagram (I could not find any references for them and my understanding is they are optional). Are you suggesting I look at the option labeled "Opt1 schematic & placement (PDF-504K) - Rev C1 -- 28 Jan 2004" and remove (shorten) the elements that are extra? Could my problem be related to faulty IC6?

Thanks,
Nick

[Reg]

Re: Hammerhead project - need help

Hi Nick,

Yes, you should use the Opt1 schematic and placement Rev C1 28 Jan 2004 as a guide. There are slight differences between what you used and this arrangement.

As for your not being able to obtain a wider range of adjustment with R 18, that is normal. All that is needed with R 18 is to be able to adjust the output to "0v" at the output of IC 6. By this I mean that once the pulse has fully decayed, the voltage should be flatlined at 0V. This should be measured with a scope if possible.

Use the values shown on the Opt 1 schematic for R 30 and R 32. It should work fine.

Adjusting R 23 will not show any obvious difference when adjusted from end to end, so don't be alarmed that you don't notice anything. I just centered this pot and it was fine, but I used matchng resistors and caps at the differential amp. I suspect you will not have any problem by just centering the pot also.

I built opt 2 so I am not sure just how opt 1 is ultimately supposed to work audio wise. As such, I can't help with any problems in that area.

Do you have a scope?

Reg

[Nick]

Re: Hammerhead project - need help

Thanks for your reply, Reg. Using R18 I am able to adjust the output from IC6 to 0.03V - 0.07V. It fluctuates slughtly, I am not sure if this is normal.

So in the end I have to do the following: remove R49, Q10, R51 and shorten R7 and R8, and connect the gate of Q3 to R9?

No, I don't have a scope. I need to find another way to troubleshoot it, or buy one

Cheers,
Nick

[Reg]

Re: Hammerhead project - need help

Hi Nick,

To be honest, I would closely follow the parts layout of the particular option you desire to build and if this means you should remove some components then I would do it, especially if a scope isn't available.

This way, you can minimize any problems. So, in answer to your question about the parts you mentioned, if they do not show up on the parts layout of the option you are trying to build, then, you probably should remove them to be safe.

I would also build a basic coil and try the PI to see just what does happen, rather than try to troubleshoot the unit piece wise.

Reg

[Nick]

Re: Hammerhead project - need help

Hi Reg,

I followed your advice and build a test coul. Connecting it to the device did not make any difference. The audio frequency is sporadically jumping up and down. Adjusting the R31 changes the frequency, but I had to also change the R30 to less than 100K in order to get low tone or clicking noise. Waiving metal objects near the coul does not seem to affect some how the device. Damn ... I am too tired to continue today.

[Reg]

Re: Hammerhead project - need help

Hi Nick,

Ok, don't get discouraged. My guess is there is a poor solder connection or something similar causing the problem. By looking at your pic, it looks like you took a lot of time to build it right.

For what it is worth, when I finished my HH, it didn't work right either. I had a solder connection that looked fine but wasn't. I just touched up the connections in the area I suspected to be the problem area and solved the problem. Hopefully, you can do the same.

Just take time to look each solder connection over carefully to make sure there are no solder bridges. If a solder joint looks questionable, I would just reheat it briefly to be safe.

After checking all the connections, I would double check the power supplies again to make sure they are at the proper voltages. They should also remain very steady.

Once the above tests are done, I would listen ver carefully to see if there is any difference in the audio signal when the coil is connected or disconnected. Also, what does the battery current do when the coil is connected. It should go up. This battery current should also vary when the pulse width is varied. Does it? Also, does it change when the pulse frequency control is changed?

I am not sure the audio is supposed to vary in frequency when the pulse freq is altered when building Option 1 design. I wouldn' think it should. However, I would expect the noise level to vary.

Hopefully, the above suggestions will help resolve the problem.

If not and you wish, you can email me and we can try to troubleshoot it via email. I can be reached at [email protected]. I don't have a HH built up at my house for the moment but I do have to build another one. So, it will take a few days before I can give any specific voltages.

Reg

[Nick]

Re: Hammerhead project - need help

Hi Reg,

Thank you very much for your effort to help me. You are right, I spent a lot of time to build this thing. I carefully measured every element before putting it on the board and I was sure it will work at once

Now about my progress. I found I did not shorten one of the resistors that are not in option 1, it was only removed. Fixing this gave me some sensitivity to metal objects near the coil. By turning controls I was able at some point to get response on Canadian dollar at about 10 cm distance. Not much. The device is still instable, or at least I don't know how to play with so many controls. I measured the current, and yes, it changes when changing the frequency from about 56 mA to about 100 mA. Without the coild the current is about 36 mA. The voltages seem right.

I can certainly take this offline and I will write you an email. I also bought the parts for the Delta Pusle project. If I can't get the HH to work, I am going to try that one.

Cheers,
Nick

[Reg]

Re: Hammerhead project - need help

Hi Nick,

It sounds like you have the HH basically working. That is a good thing. Now, it is a matter of refining each setting for the best response with the least noise. Most of this is a matter of adjustments. However, there are a few mods that can be done to improve the sensitivity and reduce the noise. Few if any of these should be done until the HH is working as well as it can, though. There is no reason to complicate things at this time.

Actually, good shielding on the coil windings will help a lot with the noise also. I imagine that you just have a basic coil in use right now, so I would expect quite a bit of noise.

As for a good working PI, I find the HH to be one of the 3 best kit type projects I have built. In fact, with a few mods, it competes quite well with some of the best.

Now, for a few questions, what size coil and how many wraps do you have on it? Also, whas value of resistor did you use for the damping resistor, R 11?.

One basic place to start is with the controls about mid position. Next, reduce the sample width (reduce the resistance R 46). This should help reduce the noise. About 1/4 turn or so from min should be fine for starters.

Set the pulse freq and pulse width at mid position and leave them there for the time being.

The main delay control, R 42, is the one that should provide the greatest sensitivity change. Reduce this control resistance until the unit no longer works and then turn it back up until it just does work. Under ideal conditions, you should be able to reduce this control to minimum and still work. However, I am sure that is not the case since it does take a few tricks to get the HH to work at less than 10 usec. The HH should work with the control at about 1/4 to 1/3 turn up from minimum resistance with about any coil less than a foot in diameter.

R 35 should be at minimum resistance for maximum sensitivity, and the autotune pot at maximum resistance. The autotune pot can be changed to a 1 meg which will help also.

Again, as for noise, all PI's are noisy, especially when testing inside a house. Without good coil shielding, there will be a lot of sputter and instability. Even with a well shielded coil the PI will most likely be quite noisy inside. Now, you should have very little noise with the coil removed. If you do have a lot of noise with no coil, then something else is probably causing problems.

Like I said, I don't have a working HH at this time, but my guess is you should be able to detect the Loony dollar at least at about 10" or about 25 cm with a decent signal when done with a 11" coil.

A DD coil will reduce the noise greatly, but again, that is a simple mod that can be done later.

If you are interested in the mods, email me.

Reg

[Nick]

Re: Hammerhead project - need help

Reg, check your email.

[Carl-NC]

Re: Hammerhead project - need help

Reg, thanks for jumping in & helping. Nick, sorry I haven't been more help, I've had no time for much of anything lately. Please let me know if you continue to have problems, I'll do what I can.

--Carl