Barracuda Legend Kit Problems

[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.

[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

[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...

[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/attac...4&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.

[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.

[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]

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.

[Qiaozhi]

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

The preamp has a gain of 1000, and the 1st integrator stage has a gain of 270. So the total gain is 270,000.
However ... you must also include the sampling gates.
With a TX pulse rate of 640, and a sampling pulse width of 40us, the sampling process has an effective gain of 0.0267.
Hence we have: 127,000 * 0.0267 = 7209. In this case, a 1uV input will result in a 7.2mV output.

[raygdunn]

Rain stops play

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

I assumed a coil core would be magnetised, but checked with a compass and it seems it is not! Not being familiar with the term ceramic magnet, I googled and found ferrite and proceeded from there☺ (I've put a ceramic magnet on order)

I have since tried a small 10mm flat disc rare earth magnet. Good range, but no joy with the test, maybe the iron content was too significant.

Final plan was to put coil on a stick to distance it from me, then wave it around in garden, whilst adjusting the second sample pulse width. I lost two 40106 chips to that. At first I thought I'd shorted something, but now I suspect the increased 11.5V+ battery supply. (LiPo supply seemed to work fine on earlier days) I was very careful the second time, but still no audio output. When more spares arrive next week, I'll try ramping up the usual 9V bench supply to see what happens. I'll suspend tests, whilst I only have the one sound 40106!

What I have noticed is that one newly inserted 40106, created very small spikes at start and end of coil pulse on the sample control pulses. I'm pretty sure that wasn't the on recent tests. But I have seen it before. Oddly one chip did survive the garden test, then showed the three extraneous mini pulses. Note that that is with the mod in place, so all voltages should have been within the same 5V range.

Time to work on fitting out the electronics box, coil housing and rewind my dodgy spider coil I think.

Ray

[Old cart]

The preamp has a gain of 1000, and the 1st integrator stage has a gain of 270. So the total gain is 270,000.
However ... you must also include the sampling gates.
With a TX pulse rate of 640, and a sampling pulse width of 40us, the sampling process has an effective gain of 0.0267.
Hence we have: 127,000 * 0.0267 = 7209. In this case, a 1uV input will result in a 7.2mV output.

How about the final DC gain stage? Does that not count?

[ivconic]

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.

Of course it would be better to improve it further.
All the time here i must admit i am not exactly sure how mentioned problem is manifesting?
Coil movements, especially fast and agile; will most probably provoke certain mum response at detector, important to emphasize is that this is so typical not only for Barracuda but also to majority of other detectors too.
Especially in closed environment. In my room almost all detectors are sensible to coil movements, due presence of various "industrial" hums and interferences.
To clear up this better; it would be really helpful to record short video on that.
Can anybody record few seconds on that?

[kt315]

How about the final DC gain stage? Does that not count?

270000x100 it is 27 000 000
who there told Bara is low sens unit?

[Qiaozhi]

How about the final DC gain stage? Does that not count?

The final stage just supplies the threshold and drives the audio stage.

[Old cart]

The final stage just supplies the threshold and drives the audio stage.

Yes but won't the audio then see that gain? That is the user interface element from coil, the headphone tone, would experience that gain.
I did not know how to calculate the integrator. Gain. Thanks.

[Qiaozhi]

Yes but won't the audio then see that gain? That is the user interface element from coil, the headphone tone, would experience that gain.
I did not know how to calculate the integrator. Gain. Thanks.

The signal chain ends at the output of the first stage, and after that the signal must be above the threshold to generate an audio tone. So the second stage only serves to boost the audio amplitude. In other words, if you increase the gain in the first stage you will increase sensitivity, albeit with an increase in instability. If you increase gain in the second stage, you will boost the sensitivity of the audio to a signal that exceeds the threshold.