I have started building my Baracuda

[Polymer]

Thought I'd share. I am excited about this and have not been active in electronics for 20 years. I realise I am enjoying this

I will be making three quick and rough coils tonite for testing and take it from there ...





I will post my results or failings (nooooo ... ) soon.

[Polymer]

Here are my three quick and rough test coils for the Baracuda:

These are my results from an air test. The ring fragment non-detection has me wondering. Any ideas?

Problems I ran into with my build:

- I was powering the Baracuda between 9.6 and 12 volts at 1.2v increments. At lower voltages the Baracuda would work fine
for a few minutes and would then beep every 10-20 seconds. I measured that the 7660 chip was only putting out a few -volts.
I tried the five different 7660's I received from Silverdog and had the same results. I thought I had a batch of bad chips at
first, but didn't want to give up and had a close look at the 7660 spec sheets as all the soldering and input voltage was fine.

What I did not understand is, what function pin 7 (osc.) has in the Baracuda circuit. It looks like it is an input pin but not an output pin?
Having a 2M2 resistor connected to it baffles me too, not much of a signal is going to get through. Any ideas on this?
I would like to see what is going on with pin 7, but I don't have an oscilloscope.

So I just disconnected pin 7 osc. and tested the Baracuda again. My negative rail -5V was working stable all the way down to 7.5V battery voltage now.

Here is what I also found when reading the spec. sheets:

When using polarized capacitors in the inverting mode,
the + terminal of C 1 must be connected to pin 2 of the
TC7660S and the + terminal of C 2 must be connected
to GND.

It looks like C2 in the Baracuda PCB I received is not correctly routed according to the data sheet of the 7660!

But the whole thing detects quite well so far and I have done no damping resistor trials yet for lack of a scope.

I am puzzled, irritated and yet happy that it is working

Any input on this????????

Thank You!

[porkluvr]

IF you don't mind telling, where did you get the stranded tin plated Teflon wire? I have recently spouted off about how the stuff is impossible to find but I would not mind being proven wrong on that count.

[Silver Dollar]

This place has some 26 gauge tinned. I believe any available is (very) old stock...
http://www.surplussales.com/Wire-Cable/Wire4.html

[Polymer]

Hello Porkluvr,

I live on an island in the Med. Sea. Can't get much stuff here and ordering stuff through the internet often incurs huge shipping costs. So I build up a shopping list which goes to my parents or friends. When I visit or they visit anything I've ordered comes along.

I traveled to Germany in July and had my latest shopping list with me for building the Baracuda not knowing where to get the stuff.

Here goes my story of how I got my coil wires:


I was on my way through some small back country towns in Bavaria in the car with relatives taking me out to some beer garden. In one of these towns I saw a wall of little plastic drawers you keep components in through a shop window. I asked my uncle to stop and let me out. I went in this shop and felt like I had time traveled. There was a friendly old man inside.


I was thrilled. I showed him my list and remarked that I didn't think places like this existed anymore. He said his shop wouldn't be around for much longer as hardly anyone builds things themselves these days and he would be quitting in September sometime. We didn't talk much after that. He hearing was not well, he was fetching parts and my relatives were getting impatient.


They had no idea what a treasure trove this was, I could have spent a lot more time there. Whilst he was fetching parts from the list I had a look at the wire rolls on the side wall. I saw what looked and felt like teflon wire and bought 30meters of each. I asked for the specs and he told me that is a surplus from a company that had it custom made many years ago and he had no information on it. There were no labels on the rolls.


Fast forward. I built the 3 different coils and tried them and was happy with that.
I wanted more of that wire and in the meantime found out that finding teflon wire
on the internet is not an easy a task as I thought it would be. I called my uncle and asked him
him to go find that shop again and get me 100meters of the blue and yellow teflon wire and to
send it to a friend who would be flying in soon.


My uncle told me the old man in the shop has no internet site and doesn't use a phone.
As far as I understood him, he opens shop when he feels like it.


I wasn't aware that teflon wire is relatively hard to get.
If it's worth getting the teflon wire I will beg my uncle to go get the rest he has.
The sooner I know the better. September is coming.


So please give me input on this.


I have measured the specs of this wire myself and tried to find it on an AWG list,
but it didn't correlate. So I have marked the parts that match.


Perhaps this is of interest to you. Can you explain it to me?


If you want some of this wire I will get it sent to you. It may take a while though.


Here's the data pic:

[porkluvr]

This place has some 26 gauge tinned. I believe any available is (very) old stock...
http://www.surplussales.com/Wire-Cable/Wire4.html

That might be old stock wire but it is not obsolete and a full datasheet is available for download.

The insulation is not exactly Teflon, but it is close enough. I think it should work very well. I have some on hand and will probably get more.

[porkluvr]

Here are my three quick and rough test coils for the Baracuda: [ATTACH]31042[/ATTACH]

These are my results from an air test. The ring fragment non-detection has me wondering. Any ideas? [ATTACH]31043[/ATTACH]

Problems I ran into with my build:
<snip>

(gees, only a short laundry list)
I believe you were mistaken when you suggested that an ICL7660 datasheet shows the capacitor (-) going to ground in the inverting mode. Please look again, it should be between pins 2 and 4.

But I do believe the PCB circuit is inadequately bypassed (not enough large capacitors in the right places). Please look in the last few pages of the Barracuda thread (or Baracuda, whatever the spelling), I believe the problem was addressed.

In the sync circuit, I would change the 2M2 resistor to around 220k, then it should work (or at least LTspice says it should).

I believe your blue wire is around 24.5AWG. If you want to be sure of what you have you could measure the bare wire diameter with a caliper then compare it to a wire gauge chart. It is a little tricky to measure stranded wire accurately, but it can be done. Don't squeeze too hard.

GOOGLE search engine will find you lots of wire charts.
You'll need more than one because not any of them will have everything you might want to know.
I hope you have a PC or other machine with a large screen because a wire chart can be challenging to digest.

-time out for me-

[Polymer]

[QUOTE=porkluvr;196013](gees, only a short laundry list)
I believe you were mistaken when you suggested that an ICL7660 datasheet shows the capacitor (-) going to ground in the inverting mode. Please look again, it should be between pins 2 and 4.
SNIP

I'm in laundry mood right now, so no problem - Thanks for your reply!

Hmmm, I did re-check 4 different data sheets and looked at the Silverdog & original Anchor pcb pictures.They appear to have the same "problem".
I do agree with you as to C1 polarity between pin 2 & 4 of the 7660. What's bugging me is C2. Here's a screenshot from one of the data sheets.
I hope it helps clarify this. The red drawing and text is from me.

[Polymer]

[QUOTE=porkluvr;196013](gees, only a short laundry list)
<snip>
But I do believe the PCB circuit is inadequately bypassed (not enough large capacitors in the right places). Please look in the last few pages of the Barracuda thread (or Baracuda, whatever the spelling), I believe the problem was addressed.

I have rudimentarily bypassed and am still learning about that and will see if I can find the posts.

In the sync circuit, I would change the 2M2 resistor to around 220k, then it should work (or at least LTspice says it should).

I will definitely try that and will post the results here.

I believe your blue wire is around 24.5AWG. If you want to be sure of what you have you could measure the bare wire diameter with a caliper then compare it to a wire gauge chart. It is a little tricky to measure stranded wire accurately, but it can be done. Don't squeeze too hard.

A single strand has around 0.25mm diameter and the whole bunch of 7 strands around 0.6mm diameter. Measured resistance at 100 meters is 9.4 Ω.

GOOGLE search engine will find you lots of wire charts.
You'll need more than one because not any of them will have everything you might want to know.
I hope you have a PC or other machine with a large screen because a wire chart can be challenging to digest.

That's why I had the feeling of going nuts with researching this AWG stuff. Thanks for this information too. I appreciate and have a big screen ...

[porkluvr]

[QUOTE=Polymer;196180]

(gees, only a short laundry list)
I believe you were mistaken when you suggested that an ICL7660 datasheet shows the capacitor (-) going to ground in the inverting mode. Please look again, it should be between pins 2 and 4.
SNIP

I'm in laundry mood right now, so no problem - Thanks for your reply!

Hmmm, I did re-check 4 different data sheets and looked at the Silverdog & original Anchor pcb pictures.They appear to have the same "problem".
I do agree with you as to C1 polarity between pin 2 & 4 of the 7660. What's bugging me is C2. Here's a screenshot from one of the data sheets.
I hope it helps clarify this. The red drawing and text is from me.

[ATTACH]31117[/ATTACH]

Do not worry about that. V+ and V- will appear the same (AC) potential to the capacitor in question. (Just make sure the (+/-) terminals face the right directions.)

edit: Please make sure you use high quality capacitors; low ESR, not surplus unknowns.

[bernte_one]

hello polymer

this is what i get
https://www.youtube.com/watch?v=tnlP...gOdhd8UOE0yWvA

i had used yv wire 0,5mm -klingeldraht- massive core (inner dia 0,5 outer 1,2mm)
32turns ond 18cm

litz wire gave me on tests worst results

so same as you has shown wich your coil comparison picture

regards from hauptstadt

[Polymer]

[QUOTE=porkluvr;196185]

Do not worry about that. V+ and V- will appear the same (AC) potential to the capacitor in question. (Just make sure the (+/-) terminals face the right directions.)

edit: Please make sure you use high quality capacitors; low ESR, not surplus unknowns.

DING DING DING - I got it ! Both ways work, except that you need a capacitor with a higher voltage rating when done the "baracuda way".
I would believe that lower voltage caps are cheaper/smaller, so why do it like they did? Easier routing, happened by chance or something I can't fathom yet?

Thanks for helping me "get" this! Here's the pic I drew to help get my brain round this:



Low ESR capacitor info gladly noted! I can be a real stickler when it comes to quality, which sometimes keeps me from finishing something

[Polymer]

(gees, only a short laundry list)

In the sync circuit, I would change the 2M2 resistor to around 220k, then it should work (or at least LTspice says it should).

-time out for me-

That did it! Changed the resistor to 220k, re-connected pin 7 of the 7660S and can operate the Baracuda down to 6.4 Volts now. YAY .
Of course the detection depth goes down as the voltage drops. Still dunno how this oscillator hookup really operates ... another day.

[Polymer]

hello polymer

this is what i get
https://www.youtube.com/watch?v=tnlP...gOdhd8UOE0yWvA

i had used yv wire 0,5mm -klingeldraht- massive core (inner dia 0,5 outer 1,2mm)
32turns ond 18cm

litz wire gave me on tests worst results

so same as you has shown wich your coil comparison picture

regards from hauptstadt

Hello bernte_one,

Thanks for the tip, I think I will be able to get that type of wire here and will try it.
Do you have any idea how it compares with teflon wire as to parasitic capacitance?

Have you ever tried Back-lack-draht? I have read about this being a wire you bake into shape. I have forgotten the name.

Would you happen to know the difference between single laquered wire and double lacquered wire
in respect to coils for metal detectors?

Thank You!

regards to alteheimat

[Polymer]

Porkluvr, I am glad you didn't want any of the blue 7 Stranded tinned wire.

Why? I just found out that it is NOT Teflon insulated, the yellow one IS.

It's PVC . I would have been very ashamed. So if I do run across tinned teflon wire
I now know to buy it all ...

Reading zillions of posts here I came to the awareness of the importance of Dielectric
Values especially in PI design. So I got the necessary infos to classify plastics.

I did some flame tests and now I know.

What wire would be better in your opinion for a PI used only in sea-water
(3.6-3.8% salinity), would it actually make a difference? Exceptionally fast delay times are
not needed here as far as I have learnt from this great website and contributors.

Here are the final specs of the two wires:

Color Conductors Insulation/mm Diameter Ω/km Finish
Blue 7x0.254 PVC 0.125 1.0mm 92 Tinned copper
Yellow 19x0.203 Teflon 0.205 1.35mm 51 Silver pl. copper

Thank You! Polymer