Barracuda Legend Kit Problems

[jladre]

kt315 is right! There's nothing wrong in the original schematic and pcb.. I have build 5 barracuda on that schematic and all working fine. So the mistake her is in you only.

[kt315]

guys, i again must notice for you - original Bara works fine.
all problems you tell about are ONLY YOUR problems. NOT of the original schematic and of the original PCB.
you do something wrong and people are thinking that Bara has problems. NOT!
i especially copied original PCB and did see no one problem.

[FatBob]

But Bara's 40106 works off 5V. This is out of its supply voltage range?

And how would you change the schematic to cure this?



Oops on some schematics it shows a 10V supply which makes more sense as
the RC's are tied to +5V but still 10V is OK for 40106.

I drew my schematic from this original traced one found online;



It shows a 5V supply for the 40106 but some of the timing resistors tie to 5V above
the positive pin!

My Silverdog / ApBerg board is built like this and I have a picture of the original it is the same.
With a gnd to -5V supply how can you use +5V for the timing?

[ODM]

If I recall correctly the Barracuda timing circuit relies on timing capacitor discharge after rising edge from the driving stage. Unfortunately there's no path to discharge that timing capacitor after a falling edge except for the IC's static charge protection diode from VSS to input pin. This is something of a serious flaw in my book, though some manufacturers' 4000B and later series will withstand abuse like that better than others, with more extensive protection networks (multiple diodes/resistors/etc). The drive current is limited in a 4000 series logic IC which may at least hit the protection diodes less hard even if it's a repeated condition. There are many Barracudas that work just fine so some parts must be good for such "cheapskate" applications.

Driving any CMOS part out of its supply voltage range is just begging for latchup. Adding small signal schottky diodes, series resistors, etc for protection shouldn't be much to ask - then again that would rob the design of its attractiveness in simplicity

[Old cart]

Hi,

I've finally cleared this problem of unwanted voltage spikes. This is what it was like [ATTACH]35502[/ATTACH] and finally I have [ATTACH]35503[/ATTACH]. Swap the chip and the problem goes away, except the first time I tried, it gradually came back! It could be caused by setting the delay trim resistance too close to zero, or it could just be me bridging pins with a probe! May be even residual power because I didn't wait long enough after switching off. A small fixed resistor in series with the Delay pot. does seem a good idea.

Sadly this doesn't seem to improve the coil movement problem any. I'll try adding those extra capacitors when they arrive and work on a more rigid standard 10" coil.

I've added to my list of identified room interference sources . An old 32" analogue TV at 2 metres. Rotating the coil to vertical avoided most of this.

Ray

Ray now that is a proper sample pulse. Check the second pulse ( the earth filed pulse ), about 100 uS later too. It is good to hear it was just a bad 40106. I wonder if a lot of these are counterfeit or just very sensitive to (static) damage. This is common with CMOS parts. I would suggest buying parts only from reputable manufacturers and touching a grounded metal plate or other point with your hand before handling these parts and soldering them in. Static straps are also a good inexpensive solution.

https://en.m.wikipedia.org/wiki/Electrostatic-sensitive_device

Impulse you might try changing this part with a brand name part. Ray has set his sample pulse just about perfectly.

Hopefully stabilizing the coil will eliminate the falsing. If it does not it may be interference, inaccurate earth field cancellation, or other system noise like a noisy 5534.

Keep us informed.

[raygdunn]

Unwanted voltage spikes in 40106

Hi,

I've finally cleared this problem of unwanted voltage spikes. This is what it was like and finally I have . Swap the chip and the problem goes away, except the first time I tried, it gradually came back! It could be caused by setting the delay trim resistance too close to zero, or it could just be me bridging pins with a probe! May be even residual power because I didn't wait long enough after switching off. A small fixed resistor in series with the Delay pot. does seem a good idea.

Sadly this doesn't seem to improve the coil movement problem any. I'll try adding those extra capacitors when they arrive and work on a more rigid standard 10" coil.

I've added to my list of identified room interference sources . An old 32" analogue TV at 2 metres. Rotating the coil to vertical avoided most of this.

Ray

[Impulse]

PI coils tend to be in the range 300uH to 500uH, whereas VLF detector normally go from 1mH upwards. Also, PI coils tend to use thicker wire than VLFs.
You would be better off buying a PI mono coil such as a Garrett Seahunter MK2, which are relatively inexpensive.

http://regton.com/10-x-14-elliptical-coil-for-sea-hunter-mark-ii.html

http://regton.com/garrett-8-coil-seahunter-mk2.html

yep i am seeing my mistake thank you Qiaozhi i do apologise for the lack of knowledge or forward thinking, i saw the coil on offer and thought i would ask/before i do, the guys in the know as i am new to the arena.

[Qiaozhi]

hey guys i still have no PC i have a new hard-drive on the way i will not give up!

if i buy a fisher f2 concentric coil would that work well with this board? (if i use the outer coil) as these are cheapish and should be well made?

PI coils tend to be in the range 300uH to 500uH, whereas VLF detector normally go from 1mH upwards. Also, PI coils tend to use thicker wire than VLFs.
You would be better off buying a PI mono coil such as a Garrett Seahunter MK2, which are relatively inexpensive.

http://regton.com/10-x-14-elliptical-coil-for-sea-hunter-mark-ii.html

http://regton.com/garrett-8-coil-seahunter-mk2.html

[Impulse]

kt315 is right. While it is theoretically possible to use a coil like this you have to really know what you are doing and probably have to cut the coil pen to modify. Not recommended.
Sorry about the PC, I have been thru this myself and it is no fun at all.

Yes he is, when i read 'VLF coil' i thought why didnt i look in to it further DUH? but that is why i like this forum so much as i can ask a question (without being ridiculed too much because i am a rookie)

[Old cart]

hey guys i still have no PC i have a new hard-drive on the way i will not give up!

if i buy a fisher f2 concentric coil would that work well with this board? (if i use the outer coil) as these are cheapish and should be well made?

kt315 is right. While it is theoretically possible to use a coil like this you have to really know what you are doing and probably have to cut the coil pen to modify. Not recommended.
Sorry about the PC, I have been thru this myself and it is no fun at all.

[Impulse]

you will first who will adaptive the VLF coil to PI detector.

and this is why i ask the guys in the know first ! thanks kt315, my lack of knowledge has shown me up again, at the very least im learning as i go

[kt315]

hey guys i still have no PC i have a new hard-drive on the way i will not give up!

if i buy a fisher f2 concentric coil would that work well with this board? (if i use the outer coil) as these are cheapish and should be well made?

you will first who will adaptive the VLF coil to PI detector.

[Impulse]

hey guys i still have no PC i have a new hard-drive on the way i will not give up!

if i buy a fisher f2 concentric coil would that work well with this board? (if i use the outer coil) as these are cheapish and should be well made?

[Old cart]

I found something interesting in my test with the ic and transistor for barracuda.. I found out that parts that from fairchild has a low performance. I place a fairchild cd40106 and i just got 10" on thin silver ring whisper sound at 10.5" but when i replace it with one come from texas inst. detection dept increase 2". Also in voltage regulator in one of my md L7812 from fairchid got extremely hot with a 21volts supply butvwhen it change with from IR regulator just warm. In power mosfet also fairchild doesnt perform well compare to branded one. I understand thier product because it come on a cheap price but if want to have a maximum performance just choose a branded product.

Parts certainly can have different performance. In the case of the 40106, which was never intended to be used as a timer, they vary quite a bit in what pulse width, and delay, they generate with the same R and C's. So while there may be other characteristics that are affecting the performance, it is likely that the sample position and transmit pulse width have
changed and that can easily change the depth of detection by 20-30%. If you have a scope it would be interesting to see the follow:
transmit pulse width- 5534 pin 6
main sample pulse delay width and timing relative to the transmit pulse above. -40106 pin 2
earth field sample 40106 pin 4- same parameters as above

[jladre]

I found something interesting in my test with the ic and transistor for barracuda.. I found out that parts that from fairchild has a low performance. I place a fairchild cd40106 and i just got 10" on thin silver ring whisper sound at 10.5" but when i replace it with one come from texas inst. detection dept increase 2". Also in voltage regulator in one of my md L7812 from fairchid got extremely hot with a 21volts supply butvwhen it change with from IR regulator just warm. In power mosfet also fairchild doesnt perform well compare to branded one. I understand thier product because it come on a cheap price but if want to have a maximum performance just choose a branded product.