Geotech Baracuda - REV-A - Project complete

[kosacid]

i stated with the coil it is 6" 0.4mm 28 turns 335uh
http://i943.photobucket.com/albums/a...161027_001.jpg

then i added a coil shield to the ground

http://i943.photobucket.com/albums/a...161028_002.jpg

then on to the build no problems there was straight forward but there was a resistor missing from the kit but i had a spare

http://i943.photobucket.com/albums/a...1104_001_1.jpg

tuning it was easy the null tuner was easy just used a volt meter and set it to voltage and pin 6 on the ic next to the null tuner and turn it till you get 0v

the delay was harder i had to use a oscope i took the reading direct of the fet, i set the pot to min and turned the tuner just at the point you get a smooth ramp up from left to right, you can do it without one just tune it till it detects and tune it back a bit, one thing i did notice it uses the full pot if its tuned right

http://i943.photobucket.com/albums/a...161114_002.jpg

testing it

i cant fault it its good on coins just about the same as the surf on gold, one thing it is quiet on the swing unlike the surf on end swings
but all in all it a really good md easy to use like the surf, my opinion i like the bara

[jladre]

I would like to buy pcb from silverdog.. does anyone knows his store location in UK? I cannot reach him in his email.

[Qiaozhi]

I would like to buy pcb from silverdog.. does anyone knows his store location in UK? I cannot reach him in his email.

Send him a PM via the forum.

[gdogg]

http://www.silverdog.co.uk/shop2/ind...product_id=105

[kosacid]

for some reason i cant edit my post but this is how i worked out the delay
for the delay i set that to 50us to match my coil rate which is 50us you can look at the rate on pin 6 of the op amp then set pin 5 of the 40106 to the same rate basically when it falls of to recovery thats how i worked out my minimal delay(set the delay pot to max resistance before testing), and once your done i used the scope to mark points on the delay dial for reference of the rates

[sinclairuser]

thanks george, finally a complete version, i totally agree with you about component tollerances, back when i was building them i had real trouble getting the same results from 2 identical builds.
one worked well enough, but the other was crap some components used in the barra are just not made to the same tollerances as before ,the 40106 was a real test and a pain, simply swapping that for a ceramic new old stock one made it a lot better.
so thats why i rebuilt that one with all top quality ceramic or metal can packages where possible, japanese caps, tested quality old stock resistors i even found 3 really old metal can tip127's.
it was like a bought detector as long as batteries are fresh when they lose power it becomes an uncontrollable monster, i always thought there was a better detector in there somewhere it looks like you found it.

[ionut_mtb]

having problem with the detection range and sensitivity. i built bara without scope, nulled to 0v, delay adjusted (when have max sensitivity just before drop and become not responsive). max detection 20cm for medium coin. AL foil not detected, small coin 5cm. coil i made one from internet network cable stripped, have like .5mm litz wire with pvc coating, 24cm diameter, 27turns. it can be the problem the damping resistor? what is the relation between damping resistor and coil value?

[kt315]

noneever relation between damping resistor and L. there is full complex value R+C+L named IMPEDANCE and THAT has the relation.
there is (exist) selfresonance of coil, the d-g R is reduction for.


see animated pic

[kosacid]

yes its your damping resistor you can prob do it manual what i did was use 220ohm resistor attached to a 1k pot with a 1k resistor across the pot to take the load, just get a small square of foil and turn it till its detected then take it off test the resistance and put in one thats closest to the value

[rankx0]

Is it possible to use any other JFETs in Barracuda? I have trouble finding 2N5485 here, and I have a plenty others. I presume J113 would be acceptable substitute. What do you think?

Also, is it necessary to use LF412, can I use any other op amp LF353, for example?

[ripsdevala]

Yes you can

[rankx0]

Thanks!

[ionut_mtb]

i found some TIP127 to order, does it feel any difference in the tone for iron? thanks

[Qiaozhi]

i found some TIP127 to order, does it feel any difference in the tone for iron? thanks

Some people claim that it makes a different sound for iron if you use a TIP127, but personally I have my doubts.
Maybe you can test this claim and report back.

[ionut_mtb]

Some people claim that it makes a different sound for iron if you use a TIP127, but personally I have my doubts.
Maybe you can test this claim and report back.

Today I replaced the irf with tip127. Now, for big targets, when it get's closer to the coil, the signal disappear. doesn't matter if is ferrous or non ferrous. the bigger the target, the bigger the distance when signal starts to cut off. I've tested with a small gold ring and the signal sounds continuously even when is close to the coil. But for one copper coin the signal disappear when almost touching the coil.