Barracuda Legend Kit Problems

[Old cart]

Thanks Old cart,

I do hate getting things wrong... I was expecting C23 to be like the rest at 220uF. I see now that the capacitor I thought was C23 was actually correctly connected C20! So C22 and C23 missing.


I'll try tacking on those two capacitors. Then maybe look at the longish power track to the logic chip. It will be tomorrow before I can try it now.

Ray

Very good. I like to reference all bypass caps to ground. There are advantages in using caps to connect +to- but it intrudes common mode noise.

[Impulse]

Hey guys I have had a chance to look at the old board and I decided to swap it for the new board to see what result I got and I had no sensitivity to movement I had the delay pot at 10k and the delay trim at 10k, I have tried a depth test and I basically have to hit the coil with my gold ring for anything to happen so i adjusted pin6 to 0v and the sensitivity was 5 inches with the same ring but I have the same issue where I cannot move it ? Shame I had a glimpse of 'wait I think it might actually freeking work!' Bit no lol

[raygdunn]

Very good. I like to reference all bypass caps to ground. There are advantages in using caps to connect +to- but it intrudes common mode noise.

Hi Old cart,
Abbreviated post as managed to lose the original...

I installed a replacement 40106 and amazingly all the unwanted spikes disappeared, and the current went down from 110mA to 90mA!
Usual pins before:

(A garden coil movement test seemed to have improved, only noticable on change of direction of swing.)

Sadly when I reconnected to grab an after image the spikes started again.. but much lower for now.

Gut feeling is that it gradually degrades with use. I am noting a spark like sound from headset on start up. I think that hasn't been there for long. Used to be a tone. I'm wondering whether there could be a voltage spike at start up.

Back to plan A and add those capacitors I guess.

Good range on a small GB 1p coin. so worth persisting I guess. :-)

Ray

[Old cart]

Hey guys I have had a chance to look at the old board and I decided to swap it for the new board to see what result I got and I had no sensitivity to movement I had the delay pot at 10k and the delay trim at 10k, I have tried a depth test and I basically have to hit the coil with my gold ring for anything to happen so i adjusted pin6 to 0v and the sensitivity was 5 inches with the same ring but I have the same issue where I cannot move it ? Shame I had a glimpse of wait I think it might actually freeking work!' Bit no lol

Have you secured the windings yet? If you have not then it is likely it will beep with movement. The reason for this was described in one of my earlier posts but basically relative coil winding movement generates a similiar signal to a target. So don't move it! Once the coil is secured and shielded then we will deal with it if it beeps. The reason it does not beep, nor does it detect the ring well when the pots are set to a high resistance is that the delay is very long and it takes a lot of metal to make a signal change down the waveform.

To illustrate this simply hook the scope to pin 6 of the 5534 and adjust for a good trace. No metal should be anywhere near the coil at this point. Now bring a large metal object like a pair of pliers near the coil and observe the change. Repeat with the ring. Tell me what you see.
then add a second trace 40106 pin two and repeat. The detector main ( target) sample is where the detector samples the signal. The more the trace moves vertically where the sample gate ( pulse ) is the better it will be detected.

You may note the the pin6 negative going pulse gets wider when a piece of iron is brought near the coil. This can cause a large vertical movement in the signal and a strong detector response.

An optional exercise is to adjust the delay and see the sample pulse move relative to the transmit pulse ( always trigger on the falling edge of the transmit pulse near the top of the positive going pulse). Take a shot where it disappears and the just reappears.

This is experiment should better help you understand how a PI detector works.

[Old cart]

Hi Old cart,
Abbreviated post as managed to lose the original...

I installed a replacement 40106 and amazingly all the unwanted spikes disappeared, and the current went down from 110mA to 90mA!
Usual pins before: [ATTACH]35458[/ATTACH]

(A garden coil movement test seemed to have improved, only noticable on change of direction of swing.)

Sadly when I reconnected to grab an after image the spikes started again.. but much lower for now.
[ATTACH]35459[/ATTACH]
Gut feeling is that it gradually degrades with use. I am noting a spark like sound from headset on start up. I think that hasn't been there for long. Used to be a tone. I'm wondering whether there could be a voltage spike at start up.

Back to plan A and add those capacitors I guess.

Good range on a small GB 1p coin. so worth persisting I guess. :-)

Ray

Ray good progress. I don't think this problem is anything other than a instrumentation problem. Low cost scopes are great for hobbiest use but you can not expect them to be perfect. They can easily be very noisy, can have poor grounding, and even inject noise back into the circuit. Indeed if you are trying to make critical analog measurements like this I would not even consider a scope that cost less 5-10,000USD.

That having been said few hobbiests have such a scope nor would I recommend that they get one unless they are very serious about electronics.

So so we have to use the scopes we have as sort of a compass to help us debug and set up the detector.

Do you happen to have a US nickel? That would be a good target for testing purposes. Lacking that we can go with a 1cm square section cut from an ordinary Coke can.

One last point, I did notice your transmitter pulse changed width. This is probably due to the fact the 40106 is a digital IC just to square up and invert a signal. They were never intended to be used as precision timing devices.

[Old cart]

For a good discussion how PIs work see here:
http://www.geotech1.com/pages/metdet...ead/HHv1p5.pdf
it is also good to buy a copy in Inside the Metal Detector described at the top of the forum. It is a great book!

[Old cart]

For all tests where we are looking at or comparing timing to the sample pulses let's try triggering on the NEGATIVE falling edge of the positive transmit pulse.

[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.

[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

[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?

[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]

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

[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]

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)

[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...r-mark-ii.html
http://regton.com/garrett-8-coil-seahunter-mk2.html