What could be wrong?

[diego]

Just soldered together my Baracuda Legend (silverdog) kit and plugged it in but can't get it to work...

When I turn it on it gives a beep and the coil starts to buzz faintly but the speaker then goes quiet and no matter how i turn the pots I cant get any sound out of it, and no response when I bring any metal over the coil

- The coil is made of laquered copper wire, 22 turns at 27cm diameter. Gives about 2 ohms
- As a power source I am using a 9V alkaline batteri. When turned on it drops to 8.3volts
- I tried to replace the small piezo with a proper speaker, but works the same way

Any ideas on what to do? Wrong voltage? Don't think any of the components are backwards and all the soldering is neat and tidy

[diego]

Got it working! The Baracuda Legend from silverdog apparently runs on 12 volts, not 9 volts (as the original). Anyone knows what the optimal voltage is? Will I get more sensitivity if I crank it up to 13-14 volts?

[sinclairuser]

twelve is fine, 13.8v is the very upper limit from my tests, but there is no real advantage running that high.

[diego]

I read on the site below (first post) about the basics of PI. Apparently the voltage makes little difference. What's more important is that your power source is able of high currents.

http://www.findmall.com/read.php?34,1777531

Have anyone tested if a switched power supply differs from a battery (8xAA or 12v sealed lead-acid)? Will it just give a lot of interference? I'm trying to find out why the depth is so low on my baracuda. Can't get the tuning right. Only 2-3" on a fork in an air test!

[Qiaozhi]

I read on the site below (first post) about the basics of PI. Apparently the voltage makes little difference. What's more important is that your power source is able of high currents.

http://www.findmall.com/read.php?34,1777531

Have anyone tested if a switched power supply differs from a battery (8xAA or 12v sealed lead-acid)? Will it just give a lot of interference? I'm trying to find out why the depth is so low on my baracuda. Can't get the tuning right. Only 2-3" on a fork in an air test!

You should really test the circuit using a suitable battery. Your power supply may not be able to provide sufficient current during the coil on-time.

[Carl-NC]

Instantaneous (pulsed) current is what matters. Usually a big tank cap is placed very close to the TX circuit to provide the pulse current so that the battery only has to provide a more time-averaged current. This would be critical if you try to use a switching power supply. Your depth problem is probably due to some other issue. Do you have an oscope?

[silverdog]

I read on the site below (first post) about the basics of PI. Apparently the voltage makes little difference. What's more important is that your power source is able of high currents.

http://www.findmall.com/read.php?34,1777531

Have anyone tested if a switched power supply differs from a battery (8xAA or 12v sealed lead-acid)? Will it just give a lot of interference? I'm trying to find out why the depth is so low on my baracuda. Can't get the tuning right. Only 2-3" on a fork in an air test!

If the fork is stainless steel, that will explain your poor detection, stainless steel is very hard to detect - test using other objects, coins, pliers etc..

[diego]

Have made some new work and put the whole thing in an aluminium casing





RGB58 shielded cable and now working on a shielded coil to go with it. It is lacquered copper wire 26 turns that I measured to about 1,5 Ohm and 430 uH.




Tried a more stable Lab PSU at the local ham schack on 11volts, but the final setup will work on either 8xAA nimh or 12v lead-acid


Connected the baracuda to an oscilloscope and measured pin 6 on the "can't-remember-the-number" and tried to get the output pulse as close to the receive signal as possible, but the closer I got the less sensitivity it gave... But this was before all the casing, shielding etc. Any ideas on other ways to calibrate it or is trial-and-error the only way?

[sinclairuser]

if you have a plug on the coil end of your coax ditch it, wire it direct to the coil(a plug on the control box end is fine), when tuned properly the barra will detect it! if you dont get falseing from it it could reduce depth.
otherwise nice clean build, i'm a big fan of the type of enclosure you used, for those on a budget the plastic(cheaper) version of that case is just as well made slightly lighter too, i really like this detector, it was the first detector project i built that actually made a proper usable detector, infact it has become my primary beach detector.

[diego]

Great input! I actually soldered on a small SMA plug on the coil yesterday but will ditch it as you said and cut open the coax

The enclosure seemed thermally better than a plastic one. Only cost 10-12 USD on ebay so not that much more compared to plastic...

I have seen all the videos on youtube where people get up to 40 cm detection in air and hopefully I will get close to that. If I do I will be one happy camper Building it was real easy but tuning it is a bit tricky...

[diego]

Now something seems wroooong. Hopefully someone can help before I smash it with a hammer....

The first picture shows the output. No problem there:


But then there is something wrong when I measure pin6 on the 40106. When I adjust the delay the spikes move in relation to each other but can't get them separated and they are not at all in sync with the output signal. Have I blown something?



The buzzer don't give any beeps, only a very very faint buzzing sound. I ditched the coax and wired the coil directly but made no difference.

[maikl]

Probably the problem is in aluminum case... attempt without...

[sinclairuser]

try it out of the case as maikl said, you could pull the chips and test your voltages(plenty of info on this in the barra threads), check traces too, a different 40106 may help too there have been some dodgy ones around lately.
in my view 40106's and 7660's are better bought as an extra in quantity, as they can have problems that are not seen until the circuit is powered those two ic's seem to be the fragile ones in the barra.

[diego]

Thanks for the tips. I never have the circuit in the casing when trying it on the scope, otherwise it would be tricky to reach the pots, pins etc

I'll dig through the huge unsorted stock at my ham radio club to see if I can't find a new 40106 to try with. Ordered some from eBay but that takes to much time...

What do you mean by "check traces"?

[sinclairuser]

what i meant by check traces is, recheck your soldering on the circuit traces, shining a good torch from underneath the board can reveal any bad contacts(not seen with the naked eye).
if you find a 40106 at your club if you have a chance get a ceramic version, its not super important but i have both and the ceramic version seems slightly better.