Another P.I. link

I have relabelled the first 741
and taken the concept off it

at the moment i'm using it on min freq and max duration to get the best depth

with that setting what is the response to gold rings ?
maybe we can do away with the pots ?

lookout world.  

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hello xavier ,

now it's been "thinned down" and "basic -ified" (new word) it's time to build on it and add more features .

and yes , the last schematic is a working one .

hello 6666 ,

detection of various metals depends on where you have set your delay / sample point and width ,

larger width = more ability to charge and discharge to holding cap resulting in a quicker responce ,

have a look back at the pic i posted earlier regarding the curve responce to various metals ,

have set mine to the middle of the decay at the moment with a 20us sample window good for all metals ,

set at the start of the slope to be more sensitive for gold and brass ,

set at the end for steel and iron ,

have tried sample at the start of the slope with a narrow sample time of 10 us , responds to gold / brass very well and lessens the responce to iron and steel.

with max pulse and min freq ,20us sample in the middle , can detect our lasses gold ring at about 25 to 30 cm

i have now done away with the freq adjust pot and fixed it at 200hz , as it didn't make much differance ,only to battery life.

volume , threshold coarce and fine is all you need i think.

as i said before would be nice to have a switch , poss 3 position to switch in 3 presets for delay / sample , start /middle and end of curve. then by listening to the respone of a target poss work out what it is , only problem is threshold would have to be adjusted every time it's altered.

oh well.

Posted on: August 13, 2011, 11:04:55 AM

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UPDATE:

just purchased an inductance meter and tested my coil ,

25 turn , 30cm dia bundled , no shield , 0.6mm wire with 0.3mm pvc covering , 1m of "mini8"coax attatched.

online calculator said it would be 380uH or there abouts ,

just measured it 527uH , nearly laughed my ar*e off !!!!

does this sound about right or is meter poss a LITTLE incorrect

if it is 527uH , wouldnt that be to slow on a PI to respond well to gold

i'm confused ,,,,,hell boy ,,,,,,we all cunfused.

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hello xavier ,

i don't have that program , have circuit maker 2000 , think its sort of similar ,

and circuit wizard , easyer to use , quicker to set up , but not very accurate for anything fast , ok for dc or slow moving stuff.

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hello xavier ,

whats your pulse width ??

notice on you posted pic it said 30us delay , is that your pulse width ??

try around about 160us pulse duration.

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I have added pins 4 &  8 to U5A


Thanks for the info on the response to gold rings
I have to do some domestic stuff, back later.

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