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**6666** · 03-03-2016, 01:30 AM

Try here
http://www.geotech1.com/forums/showt...uction-details

**raygdunn** · 03-03-2016, 01:41 PM

Originally posted by Michaelo View Post

Can anyone direct me to the correct schematic for Baracuda (Rev2 Alex/Ap as supplied by silverdog 2016)?
Have any changes been implemented to improve this design I should know about so I can implement them

Hi Mike

kt215 has kindly produced a more up-to-date schema, fixing bugs in the original. (Check out the immediately preceding posting to see fixes from the original in the project sticky.)

http://www.geotech1.com/forums/showt...367#post213367

This schema does include the pin pointer feature, which has been bypassed in the current kit. The audio output can vary. The kit supplies a buzzer. One can easily add the LED, speaker or socket for a headset.

Other differences in the kit: The external delay pot is bypassed with a link, so is now an optional extra; the multitude pots are 20K and in my case the coil resistor is 390 ohms rather than 330 (we will all try to increase this significantly anyway I expect ☺);

(I cut the delay pot link, added the external pot, plus another 12K to make the delay suit my test coil... This worked, but it then dawned on me that my spider style coil probably has a short in its winding, making it extremely "slow". I changed to a conventional 10" coil and the 20K is now sufficient.)

As an amateur electronics enthusiast, I can highly recommend reading "Inside the Metal Detector" associated with this forum. This should be the revised version with a number of diagram typos fixed.. and the price has gone down too☺

http://www.amazon.co.uk/Inside-Metal...metal+detector

I clocked up about 40 hours detecting last year with a PI-1 based design from the book, patch boarded, then transferred to Veroboard. All aimed at giving me enough understanding to debug a kit. It will be interesting to compare it with the Barracuda. If you happen to read "The Register", with it's obscure units of measurement, I'd rate the PI-1 as "four spanners to the acre". No lack of ancient tractor parts under our fields it seems.

Ray

**kt315** · 03-03-2016, 03:08 PM

Can anyone direct me to the correct schematic for Baracuda (Rev2 Alex/Ap as supplied by silverdog 2016)?

enjoy

Attached Files

Barracuda_sch.gif (160.1 KB, 614 views)

**6666** · 03-03-2016, 08:38 PM

I clocked up about 40 hours detecting last year with a PI-1 based design from the book,

Did you build it exactly as the book says or did you change something ?

**Michaelo** · 03-03-2016, 10:15 PM

@6666 ... many thanks got that one...

@ray, lots of info there... the other mods have varying results according to the posts so I will leave them for later... Might pick up the book though...

@kt315, this one seems to be better but it's missing supply voltage for 40105 (probably +/-5 volts but on some schematics it's 0 volts (ground) and -5)... also missing U2 supply... again must be +/-5 volts.

Thanks guys, I'm a bit closer to unravelling the mystery...

I'm an old engineer and should be able to work this out but when it comes to metal detectors, it's a black art... anything is possible

Mike

**kt315** · 03-04-2016, 03:40 AM

Originally posted by Michaelo View Post

@
@kt315, this one seems to be better but it's missing supply voltage for 40105 (probably +/-5 volts but on some schematics it's 0 volts (ground) and -5)... also missing U2 supply... again must be +/-5 volts.

Thanks guys, I'm a bit closer to unravelling the mystery...

I'm an old engineer and should be able to work this out but when it comes to metal detectors, it's a black art... anything is possible

Mike

ok. you can make sure yourself that all traces are ok on board.

http://www.geotech1.com/forums/showt...oards-for-sale

**Michaelo** · 03-06-2016, 04:59 PM

I'll trace the board I'm using as there may be some differences...

Does anyone know what the current requirements are for the +/- 5 volt supply?

I will be able to answer this and other when the rest of my parts arrive (slow boat from China) but in the mean time I'm just trying to simplify the design...

One more question... has anyone published a full set of oscilloscope images from working board that can be used as a working reference?

**raygdunn** · 03-08-2016, 02:44 PM

Originally posted by Michaelo View Post

I'm an old engineer and should be able to work this out but when it comes to metal detectors, it's a black art... anything is possible

Mike

I heartily agree about the black art bit. The number of factors to be "tuned", for that extra bit of depth, or even to get a working detector, is huge. I had no idea what I was getting into ☺

I originally came here looking for a kit to build. I used to build my own radio control equipment, radios and the like in my youth. I lost interest when the electronics started disappeared into mysterious black boxes.

On becoming "mostly retired", I found that the challenging kit producers from that time had disappeared. The new equivalent is I guess the "Maker" network and playing with flexible computers like the Raspberry Pi. Commonly taking electronic units and repurposed them. You will see that in some of the latest projects here with the reply signal processing getting ever more clever.

Modern metal detectors are a good challenge to build. Have fun ☺

Ray

**kt315** · 03-08-2016, 02:58 PM

Originally posted by Michaelo View Post

One more question... has anyone published a full set of oscilloscope images from working board that can be used as a working reference?

for what? the schematic is simple, all proceses are clear evident. board starts to work just you turn it up. seems you have much time to do remakes.

**raygdunn** · 03-08-2016, 03:30 PM

Originally posted by Michaelo View Post

this one seems to be better but it's missing supply voltage for 40105 (probably +/-5 volts but on some schematics it's 0 volts (ground) and -5)... also missing U2 supply... again must be +/-5 volts.
Mike

On Silverdog's board, I've traced the 40105 supply back to the 5V from the 79L05. Definitely no more than the 5V on this one. One imagines it might be more stable on the 78L05. This may reflect the original commercial design it's based on. And there would be complications with VT3 and VT4, which are not voltage decoupled.

I haven't traced it, but U2 will be the 10V like U1. Allowing the op. amp. 5V swing either side of earth. I guess audio is on the full battery voltage to reduce load on the regulators. That makes sense. A slight positive rise from earth voltage and VT6 switches on.

I'm missing a lot of the subtlety of the circuit, like the effects of VD5 and VD6, which must clip one side of the signal. It might be useful to vary the main timing pulse width to limit pulse current on a low resistance coil. A wild guess would be to change the ratio of R7 to R8. It is of course a chance to learn about the online circuit simulator frequently referred to in the forum.☺

Ray

**kt315** · 03-08-2016, 04:15 PM

http://storage9.static.itmages.ru/i/...c53e7d5a29.jpg

**kt315** · 03-08-2016, 05:28 PM

http://storage5.static.itmages.ru/i/...67fa3f385a.jpg

**Michaelo** · 03-08-2016, 09:30 PM

@Ray...

Something weird with this forum software...
I just replied to your post but before hitting the submit button I opened my profile page (in another tab) and when I came back to post my comment it had disappeared...

Originally posted by raygdunn View Post

I heartily agree about the black art bit. The number of factors to be "tuned", for that extra bit of depth, or even to get a working detector, is huge. I had no idea what I was getting into ☺

I originally came here looking for a kit to build. I used to build my own radio control equipment, radios and the like in my youth. I lost interest when the electronics started disappeared into mysterious black boxes.

On becoming "mostly retired", I found that the challenging kit producers from that time had disappeared. The new equivalent is I guess the "Maker" network and playing with flexible computers like the Raspberry Pi. Commonly taking electronic units and repurposed them. You will see that in some of the latest projects here with the reply signal processing getting ever more clever.

Modern metal detectors are a good challenge to build. Have fun ☺

Ray

Absolutely agree...

I also came to build a kit or two and by doing so I hoped to to learn all about metal detection so I can build an open hardware version (primarily because commercial version are too expensive).

For the last few years I've been interested and involved in the Makers, Pi and Arduino communities but it hasn't been easy, I have had to relearn quite a bit... I only mention this as people assume as an old engineer I should know this stuff...

Mike

**Michaelo** · 03-08-2016, 09:36 PM

Originally posted by kt315 View Post

http://storage5.static.itmages.ru/i/...67fa3f385a.jpg

@kt315, can you post that image without the the pop-up (Edit Nets window), that way I can see the rest of the traces?

Mike

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