Problem detecting gold on surf pi 1.2

[mellao]

Hi,
this is my first post, so I would like to talk about me and my problem
I'm Carlos (mellao), from Spain, and I'm a little noob in this metal detectors world
I bought a surf pi 1.2 from silverdogs and I build it, and check the components a lot of times and it seems to be OK.
I did a coil with a enamelled wire 0.5mm, with 23 turns and 17cm of diameter.
I adjusted the offset on pin 6 of NE55 to have 0v.

So the problem was....:
I have response when moving the potentiometers, but, coil only detect medium objects (knife, scissors) maximum at 7cm, or small objects (coins) nearest to the coil.
This does not detect gold rings, even I pass through the coil, only beeps if I touch the coil with the ring.

I was looking for this problem in this forum but I doesn't get anything clear...

Anyone knows what could be the problem?

Thanks for your time!!

[daverave]

you need to adjust the delay pot so the detector becomes more sensitive to low conductive items like gold...if you dont have a oscilloscope then adjust the delay pot slowly either way so the detector starts to become jittery on the audio.

[mellao]

Thanks for your reply daverave!
now it works... Sorry for that mistake, I don't know why but I thought delay pot only has 1 or 2 turns on the screw.
I did a lot of turns (maybe 20) on delay pot until I heard a "click" on every more turn. (It means that I reached the final value)
Then, I was trying with gold and moving the screw to the opposite direction and I was able to adjust it


Now is detecting a gold ring at ~13cm


Thank you!!

[daverave]

glad you got your detector working but you should be able to get more depth than 13 cm which is only about 6 inches....with my surf pi i can get around 15 - 16 inches whisper on a small 9ct gold band ring....but to do this the circuit has to be modified and you need some understanding of doing these modifications.

[KORRIGAN]

hi
can you explain the changes in order to get these performances?
I"ve got a silverdog kit too.
thanks in advance

[silverdog]

try making another coil - from the dimensions given your coil is around 256uH, this would be ideal for surf pi but baracuda may work better with a little higher inductance
The coil calculator here will help http://www.geotech1.com/forums/showt...oil-Calculator
You coil is only 15cm diameter so 13cm detection is actually pretty good for first attempt
Other quoted distances are almost certainly using larger coils, 25cm is pretty standard

[kenny444]

Hello with regards to depth I am struggling too. I have made coils from Enamelled copper, multistrand, teflon coated mutil strand, I have made coils from 8" to 14", I have made round, square and oval coils, I have used the coil calculator and used two different meters to measure the inductance to confirm my 300uH target, I have made 3 x Surf PI 1.2 units, I have checked the offset with meter and scope, I have adjusted the delay pot to both limits with and without a scope, I have used an adjustable damping resistor to get optimum, I have changed all the IC's to different variants. All voltages are correct. Sadly I can only get about 7" on a pound coin air test? I use separate voltage checked power packs, I have no more ideas. But Daverave gets 15-16 inches, WOW........... well How really

[kenny444]

glad you got your detector working but you should be able to get more depth than 13 cm which is only about 6 inches....with my surf pi i can get around 15 - 16 inches whisper on a small 9ct gold band ring....but to do this the circuit has to be modified and you need some understanding of doing these modifications.

Please list these wonderful mods. Thank you.

[daverave]

Hello with regards to depth I am struggling too. I have made coils from Enamelled copper, multistrand, teflon coated mutil strand, I have made coils from 8" to 14", I have made round, square and oval coils, I have used the coil calculator and used two different meters to measure the inductance to confirm my 300uH target, I have made 3 x Surf PI 1.2 units, I have checked the offset with meter and scope, I have adjusted the delay pot to both limits with and without a scope, I have used an adjustable damping resistor to get optimum, I have changed all the IC's to different variants. All voltages are correct. Sadly I can only get about 7" on a pound coin air test? I use separate voltage checked power packs, I have no more ideas. But Daverave gets 15-16 inches, WOW........... well How really

the things that you have done with your surf pi unit's are good but to get more depth the circuit has to be altered somewhat...and my coil is just normal single strand copper wire with an inductance of 400 uH....the gold ring as stated i can get 15-16 inches whisper but on a nickle old half crown i can get 21-22 inches whisper...and these depths are in air and maybe more in ground.