Barracuda Legend Kit Problems

[Old cart]

That is true.
That is why i said it is most desirable "small and cheap" diy PI project.
You get a lot from it for such small investment.
...
Just a thought, when having "coil motion problems": what kind of coil cable is used?
Anything else but good coaxial cable will simply not do.

Ivconic, agreed. So would it not be better if we can make changes so more of the detectors perform well rather than just some?
Have you found your Bara's to be unusually sensitive to coil movement?

This circuit has a lot of gain, as I recall about 27 million. If this is right 37nV gives 1 volt of output.

[Old cart]

Here u go.. Top trace is pin 2. Bottom is pin 4.
Sweep = 50uS/ div
Y axis is 2V/ div.

Pulse is essentually returning to ground from -5V. I have my scope ground reference on the minus lead of C1.

Don, those look very clean, there is no spurious signal riding on them as we have seen. The earth field pulse looks a little narrower than the main sample pulse. Maybe not enough to be an issue. It appears like the 40106 is working great.
Can you also repeat with the preamp out pin 6 and main sample use shown on the same trace? Trigger on the negative going edge of pin 6 above ground and maybe 10 uS per div. Looks like you have a good old hp analog scope there. is the 20 MHz bandwidth limit on?

[Old cart]

Thanks Koala,

Liquid flux is new to me. My existing solder wick probably goes back to ~1970. I seem to remember not being able to generate enough heat to use it back then. Metallic mesh that conducted heat away fast. Probably partly bad technique.

Fine wire cutters is another of my shopping items. Mine seem designed for mains cable and useless on these small PCBs. Another case of not going cheap to get a good edge, I suspect.

Ray

This brings back memories... If your are doing much electronics work there are several things that make a huge difference.
-A temperature CONTROLLED soldering iron. These have a much larger heating element that switches on and off to maintain temp. Because of this they can solder huge wire as well as the smallest component without burning anything up.
-Rosin based flux. Not sure you can still get this but is applied to the board before soldering.liquid is more convenient.
- A moist soldering sponge or wire mesh tip cleaner. You should clean the tip and tin if before each use or whenever it fails to solder satisfactorily.
- A good small pair of side cutters. This will be fairly expensive if good maybe $15 USD. Never cut anything except small electronic components with them.
- I much prefer lead based solder. Again not sure if you can still get this. I bought several pounds when they were phasing out lead in the US.
- Also handy-wooden tooth picks or a high heat resistant soldering aid to clean out holes.
- De-Soldering wick w/ flux imbedded or a solder sucker. I prefer the former. Some solder suckers are too violent and can damage the board.

[dfbowers]

Don, that is good info. I would not argue that point. My thinking has changed somewhat. While I still believe it is necessary to have a stable coil with no windings moving relative to one another, it is looking more and more like the 40106 is being pushed beyond it's limits. When this happens the part degrades and causes extra sample pulses, both the main and earth field pulse, to be generated at incorrect times. These extra pulses cause instability and noise . For an example see here:

http://www.geotech1.com/forums/attachment.php?attachmentid=35414&d=1457211532

if you look at the datasheet for the 5485 switches you can see that they will be in part on mode with these voltages applied. Worse the amount that they are turned on varies with temperature and supply voltage.

http://www.utdallas.edu/~jblee/EE3110/2N5485.pdf

So those extra sample pulses in the earth field could be causing the earth field to be flawed thereby causing this sensitivity.

At this point this is an educated guess. We have not proved it though Ray wil be doing some tests to confirm. George is also investigating. We have have successfully tried pulling the device inputs to ground rather than +5 and so far that appears to work, but does require changing 3 resistors. It also may prevent the 40106s from degrading.

It appears that many have Bara's that work then fail, and some have Bara's that work very well for a long time. Several others have expressed concern over the quality of the design. I suspect that the design is flawed and needs a little work.

Perhaps that is why the company went out of business.

Don could you measure and submit photos of the 40106 pin 2 and 4 waveforms measured relative to ground from Bara 2 above? That might help us figure out what is going wrong.

Here u go.. Top trace is pin 2. Bottom is pin 4.
Sweep = 50uS/ div
Y axis is 2V/ div.

Pulse is essentually returning to ground from -5V. I have my scope ground reference on the minus lead of C1.

[ivconic]

i used 0.5mm enamelled copper wire for all of the coils the first one was a simple bunched then i tried the self shielding type (spider) then for the last attempt i spent ages winding a flat spiral coil. The first coil wasnt bad the spider coil wasnt great and the spiral wound was the best.

Such coil and coaxial cable are just fine.
So it's not about coil and cable...

[raygdunn]

Quality of solder wick makes a big difference.

Loctite branded just works well

Bought some cheap of DX.COM useless unless you add some liquid flux first.

Thanks Koala,

Liquid flux is new to me. My existing solder wick probably goes back to ~1970. I seem to remember not being able to generate enough heat to use it back then. Metallic mesh that conducted heat away fast. Probably partly bad technique.

Fine wire cutters is another of my shopping items. Mine seem designed for mains cable and useless on these small PCBs. Another case of not going cheap to get a good edge, I suspect.

Ray

[Impulse]

Out of curiosity how was the original coil made. Solid wire or coated stranded wire. Suspect solid wire would be used as the original only went down to 22 uS

i used 0.5mm enamelled copper wire for all of the coils the first one was a simple bunched then i tried the self shielding type (spider) then for the last attempt i spent ages winding a flat spiral coil. The first coil wasnt bad the spider coil wasnt great and the spiral wound was the best.

[Koala]

Thanks for the advice guys. I have a solder sucker, but I suspect the nozzle is too large.. And not very heat resistant. Time for an upgrade I think☺

I've not been very successful with the solder wick in the distant past. Time I tried it again.

Good point about the drilling. I was enlarging the holes very slightly.

Ray

Quality of solder wick makes a big difference.

Loctite branded just works well

Bought some cheap of DX.COM useless unless you add some liquid flux first.

[Koala]

Out of curiosity how was the original coil made. Solid wire or coated stranded wire. Suspect solid wire would be used as the original only went down to 22 uS

[Impulse]

That is true.
That is why i said it is most desirable "small and cheap" diy PI project.
You get a lot from it for such small investment.
...
Just a thought, when having "coil motion problems": what kind of coil cable is used?
Anything else but good coaxial cable will simply not do.

I started off with a 2 core foil wrapped shielded cable and was told that it probably had to much capacitance so i changed it to coax, i will post my barracuda to qiaozhi today (if i get the chance, busy week!)

[ivconic]

Sure can. Give me a day or so and I can post. I could actually do it for 2 builds that have the problem. I did substitute a couple 40106s in last night.. different manufacturers with no change in symptoms. I also changed coils with another PI machine I have that is working just fine (not a Baracuda). No change..
I think this issue is worth fixing. When the Baracuda works it works very well. I dug a lot of deep stuff in the surf two summers ago.

That is true.
That is why i said it is most desirable "small and cheap" diy PI project.
You get a lot from it for such small investment.
...
Just a thought, when having "coil motion problems": what kind of coil cable is used?
Anything else but good coaxial cable will simply not do.

[Old cart]

Hi,

Thanks for your advice.

I replaced the 13K with a 3K fixed plus 10K variable. Also went the other was and used a 10K fixed component. However I couldn't find a quiet spot. I may have been pushing things by using an old medium wave aerial, which would be relatively powerful. Detection range was approaching an inch I would say. Only detectable swinging past one edge of the 10" coil.

At times I did have trouble with a beat frequency, which drifted through the zero point. That was when the threshold was set towards maximum noise. I don't understand the audio process. It feels a bit like it's using positive feedback like the old super-regen radios. .☺

I can probably find a ferrite ring if that would be better for testing.

Ray

Are you saying you used a ferrite rod for the field testing? If so it has to be magnet, it must attract iron.

[dfbowers]

Don, that is good info. I would not argue that point. My thinking has changed somewhat. While I still believe it is necessary to have a stable coil with no windings moving relative to one another, it is looking more and more like the 40106 is being pushed beyond it's limits. When this happens the part degrades and causes extra sample pulses, both the main and earth field pulse, to be generated at incorrect times. These extra pulses cause instability and noise . For an example see here:

http://www.geotech1.com/forums/attachment.php?attachmentid=35414&d=1457211532

if you look at the datasheet for the 5485 switches you can see that they will be in part on mode with these voltages applied. Worse the amount that they are turned on varies with temperature and supply voltage.

http://www.utdallas.edu/~jblee/EE3110/2N5485.pdf

So those extra sample pulses in the earth field could be causing the earth field to be flawed thereby causing this sensitivity.

At this point this is an educated guess. We have not proved it though Ray wil be doing some tests to confirm. George is also investigating. We have have successfully tried pulling the device inputs to ground rather than +5 and so far that appears to work, but does require changing 3 resistors. It also may prevent the 40106s from degrading.

It appears that many have Bara's that work then fail, and some have Bara's that work very well for a long time. Several others have expressed concern over the quality of the design. I suspect that the design is flawed and needs a little work.

Perhaps that is why the company went out of business.

Don could you measure and submit photos of the 40106 pin 2 and 4 waveforms measured relative to ground from Bara 2 above? That might help us figure out what is going wrong.

Sure can. Give me a day or so and I can post. I could actually do it for 2 builds that have the problem. I did substitute a couple 40106s in last night.. different manufacturers with no change in symptoms. I also changed coils with another PI machine I have that is working just fine (not a Baracuda). No change..

I think this issue is worth fixing. When the Baracuda works it works very well. I dug a lot of deep stuff in the surf two summers ago.

[raygdunn]

Your timing looks fine except the 2nd pulse is too wide. The pulse controls how much earth field cancellation you have which keeps the detector from sounding when you move the coil in the earths magnetic field. You could parallel that resistor then adjust your 100K pot for 44uS. Disconnect and measure the pot then solder that value of fixed resistor parallel to the one on the board. No need to remove the resistor on the board.

An even better method might be to adjust for 44us then wave a small magnet ceramic magnet near the coil, adjust the pot for minimum response to the moving magnet. I think it is better not to use an iron magnet.

Hi,

Thanks for your advice.

I replaced the 13K with a 3K fixed plus 10K variable. Also went the other was and used a 10K fixed component. However I couldn't find a quiet spot. I may have been pushing things by using an old medium wave aerial, which would be relatively powerful. Detection range was approaching an inch I would say. Only detectable swinging past one edge of the 10" coil.

At times I did have trouble with a beat frequency, which drifted through the zero point. That was when the threshold was set towards maximum noise. I don't understand the audio process. It feels a bit like it's using positive feedback like the old super-regen radios. .☺

I can probably find a ferrite ring if that would be better for testing.

Ray

[Old cart]

BAracuda needs some redesign?

Hey guys.
I have been following this thread for the last few days. This thing about the coil motion problem seems all so familiar! I have built three Silverdog kits so far. The first one worked like a champ for a couple of season. Then it died and for the life of me I could not resolve it. I built a second. It works well but suffers badly from coil motion problems. I used it at the beach last summer well away from electrical noise sources. The coil is shielded and potted. Same coil as Baracuda #1. I tried matching resistors and FETs without success. So.. I built a third paying careful attention to detail. Same problem : / I cannot offer a solution at this point. But can only suggest that it's not just one or two builds with the same issue. I have pretty much ruled out electrical noise and unpotted or unshielded coils as the sole source.
Don..

Don, that is good info. I would not argue that point. My thinking has changed somewhat. While I still believe it is necessary to have a stable coil with no windings moving relative to one another, it is looking more and more like the 40106 is being pushed beyond it's limits. When this happens the part degrades and causes extra sample pulses, both the main and earth field pulse, to be generated at incorrect times. These extra pulses cause instability and noise . For an example see here:

http://www.geotech1.com/forums/attachment.php?attachmentid=35414&d=1457211532

if you look at the datasheet for the 5485 switches you can see that they will be in part on mode with these voltages applied. Worse the amount that they are turned on varies with temperature and supply voltage.

http://www.utdallas.edu/~jblee/EE3110/2N5485.pdf

So those extra sample pulses in the earth field could be causing the earth field to be flawed thereby causing this sensitivity.

At this point this is an educated guess. We have not proved it though Ray wil be doing some tests to confirm. George is also investigating. We have have successfully tried pulling the device inputs to ground rather than +5 and so far that appears to work, but does require changing 3 resistors. It also may prevent the 40106s from degrading.

It appears that many have Bara's that work then fail, and some have Bara's that work very well for a long time. Several others have expressed concern over the quality of the design. I suspect that the design is flawed and needs a little work.

Perhaps that is why the company went out of business.

Don could you measure and submit photos of the 40106 pin 2 and 4 waveforms measured relative to ground from Bara 2 above? That might help us figure out what is going wrong.