Baracuda Build (silverdog kit Rev2)

[raygdunn]

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

40 years a programmer, I enjoy playing with the Pi (Pi 3 will be interesting :-) ), worked with Linux for years, but the Arduino etc. will be a new challenge here.

Ray

[Michaelo]

@Ray
Similar time frame... DOS programming (mostly pre windows) about 10 years and last 10 years mostly web development php/css/html/javascript...
And at the same time, electronics (service/R&D/development/manufacturing)...

Last few years mostly Arduino and IOT... I love learning but ever more I love making things

Do you do any Apps development (IOS/Android)?
Mike

[Michaelo]

@kt315.... sorry I just noticed the 40106 is connected to Ground and -5 volts but on silverdogs it's +/- 5 volts...
Both will work obviously but does anyone one know the reasoning behind the change?

Can't help thinking it would be better connected to +/- 5 volts...
Mike

[kt315]

but on silverdogs it's +/- 5 volts...

@mike. is silverdog the developer of the schematic? or Jim Pugh passing away from you an unknown man?
why you so want to change something in the design?

[kt315]

@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

[Michaelo]

but on silverdogs it's +/- 5 volts...

@mike. is silverdog the developer of the schematic? or Jim Pugh passing away from you an unknown man?
why you so want to change something in the design?

I'm new to all this, I don't know who designed the board or the layout, I just want to experiment.
I also assume the design is in the public domain and there are no issues with building or modifying it?
...

Here are some ideas I want to try implement...
First I need to design some circuitry that works well and detects everything...
Next, add the ability to save data so I can later analyse it (a scan of the detection to build a database of found items)...

The main aim is to try build a system that can help distinguish between different items and avoid digging up unwanted stuff...

Another idea involves using a microcontroller to sweep the transmit pulse frequency slightly and possibly the delay in order to maximise the response during detection...
Not sure if this would be of benefit but it would be worth experimenting with...
...

So before I can build my own metal detector, I need to fully understand exactly what's involved and precisely how they work, then I can design a good one...
Although I understand the underlying principles, there are areas that remain unclear...
Mike

[6666]

I also assume the design is in the public domain and there are no issues with building or modifying it?

No issues.

[silverdog]

The board in my kit was designed by APBerg
If you look in this thread you will see where it all started
http://www.geotech1.com/forums/showt...light=baracuda

[kt315]

my layout
- where possibly almost all traces were doubled on both sides
- power supply traces to preamp were optimized for low noise factor
- on every IC was set a tantalum on bottom side
- you can set on r15 and r16 inductancies instead resistors, 80-100uH

[Michaelo]

A small correction:

I stated earlier that on this revision of the PCB the supply voltage for the 40106 IC was +/- 5 volts... that was incorrect... it's Ground (0 volts) and -5 volts...

There has been quite a lot of posts questioning this fact but as the original appears to have used these values it is assumed they are right...
I personally would prefer +5 and -5 but either way it makes very little difference... (as long as pin 14 is positive with respect to pin 7, the IC is happy enough)...
To my knowledge this IC has been used as a level shifter/converter so that fact that some inputs are at +5 should have no adverse affects...

Setup:
Connect your meter to pin 6 of the NE5534A and Ground (NE5534 is U1 on some but in my schematic it's U2)...
Adjust offset voltage using the trim pot (beside the NE5534 IC), until it measures 0 volts (might be a few millivolts either way)...

The delay adjust using trim pot R10 is best adjusted with a scope but if you don't have one, turn R10 fully clockwise, then slowly turn anti-clockwise until you hear a bleep...
This will get you close and your detector should detect metal, mind you, mine wasn't all the sensitive (I have some electronic equipment around the place and I gather it can affect things)...

Obviously this is not an official method, it's just how I got mine up and running and might be of help to others... it might be completely wrong, but I could not find a de facto method...

Delay circuitry missing a resistor:
The delay circuit should delay the signal between 20 and 60 microseconds (according to the schematic), however, the delay trim pot is connected between the input and ground, therefore if you turn the post fully clockwise, you actually ground the input causing the detector to stop functioning... A resister should be connected in series with the trim pot to establish the 20 microseconds minimum...

Also as the delay is the only method of affecting the devices sensitivity, it seems strange it was removed, I would add it back and use the trim pot for setting the minimum delay only...

Baracuda Operation Notes:
Just a short note as to the operation of the detector... see attached image...
The output of the amplifier saturates and then goes negative for a short period and then recovers... If we introduce some metal to the coil we modify the recover time so that it falls within the delay window...
Of course this is conjecture based on what I observed... a detailed explanation will follow just as soon as I have one...

http://www.phpbbireland.com/kiss2/download/file.php?id=1640&t=1

Mike

Note to admin... Can't attach image... several javascript errors encountered...

[Qiaozhi]

Note to admin... Can't attach image... several javascript errors encountered...

Click on the Go Advanced button, and scroll down to Manage Attachments.

[Michaelo]

I'm posting my coil info, appreciate any comments as I don't know if it is correct for the bara...

Wire = 0.5mm 24AWG (enamelled coated copper)
Coil diameter = 200mm (8") with a resistance of ~1.9ohms and 530µH (0.53mH)
Detection distance for small coins in not that great (I assume) at about 4 to 6 inches...
Larger objects such as small aluminium heatsink (1.5"x1.5x"0.5") and a small metal wrench 6" ~ 8"...

Mike

[kt315]

turns? how much -?

[Michaelo]

I actually messed up on the counting and didn't unwind it but at a guess it was about 24 - 28...
I will count the turn when I get a chance and post an update...

[kt315]

that's ok. calculator gives right value.