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Offline Logenxxx
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« Reply #320 on: April 07, 2010, 07:31:21 pm »
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hello Raff33,
as what hesamavr said is true but you must follow the schema for R5 should be 560ohms. c30 and c31 is too much but no problem, better remove the other cap. to save a component but this has no further effect too.
if you have an oscilloscope, try to check the test points.
you can download oscilloscope software in download area. just read the help file before using it.

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Offline BR*simonn
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« Reply #321 on: April 07, 2010, 09:53:13 pm »
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Hello my friend. Can you help me?
what's the correct value of R5? 560 or 680 ohms 1w ?
Thank you.
Claudio

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Offline Logenxxx
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« Reply #322 on: April 08, 2010, 03:03:45 am »
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hello Claudio!!!
sorry for my latest reply. R5 is 680ohms 1 w. i posted a mistake

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Offline raff33
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« Reply #323 on: April 08, 2010, 09:43:57 am »
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hello Logenxxx ,
thanks for helping .......
 - R5 =680ohms 1 w is ok for big coil 1m*1m ?
 - I mesure the resistance of my coil : 40cm diameter ; 0.50mm wire ;  it's ok (3ohms) but after soldering the cable with the coil i mesured (4 ohms)  Shocked .
 - resistance coil must be 3ohms with cable or without....?
Regards....raff

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« Last Edit: April 08, 2010, 09:46:47 am by raff33 » 		Logged
Offline hesamavr
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« Reply #324 on: April 08, 2010, 10:35:13 am »
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3OHM is resistance of coil. use shielded wire, and don't use long wire for connection. make it as short as possible.

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« Reply #325 on: April 08, 2010, 11:30:26 am »
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Thank you again my friend Logenxxx.
Claudio Great

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Offline raff33
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« Reply #326 on: April 08, 2010, 06:02:23 pm »
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hello hesamavr,
 - R5 =680ohms 1 w is ok for big coil 1m*1m ?
thanks for helping....... Wink


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Offline hesamavr
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« Reply #327 on: April 09, 2010, 02:41:19 am »
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Dear Raff33
I've checked both 2K2 and 680R resistors with 45cm coil. I didn't see any difference, but maybe it has influence in higher frequency or bigger coil. for further professional adjustments you must have oscilloscope. my DP didn't detect a 2.5cm coin more than 20cm with 45cm coil. and I want to modify circuit with some changes and instrumental adjustments.

Try 1K,1W. I think it should be best choice.

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Offline raff33
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« Reply #328 on: April 09, 2010, 03:20:36 am »
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hello hesamavr,
my DP detect 1 euro at 28cm with  coil 40cm diameter,but with 1m*1m detect iron plat 45x25cm at only 2 meters ........and the same result with 2K2 1w - 680R 1w - 1k100 1w  Sad
why do you use shielded wire ? i think it's not for mono coil.........how you connect the shield......?
i think cable (2wires 1.5mm) without shield is good.
Regards..raff


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Offline Logenxxx
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« Reply #329 on: April 09, 2010, 04:44:25 am »
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Hello Raff33, Hesamavr and Cludio!!!
My search coil which is 8 inches or 20 cm octagonal coil can detect a 2.5cm coin at 34 cm in free space but it can not detect a tiny gold ring.

I uploaded here the pictures of the coil. It was wound in an old crt monitor stand. I cut the center of the stand by a coping saw so that only the circular edge remain as you can see in picture. Then i wound the coil at the bottom as you can see also in picture.

The center support and half handle was made of pvc pipe and the other half but extendable to double size was from an old damage glass wipe cleaner.

I did never made a revision from the schema posted by Eugene.
hello Raff33!

no need to shield the wire, it is a shielded cable wire used in cable tv or any radio transmitter. it is either rg58, rg58, rg 117 etc. don't use too long cable. 3meters long is maximum. i only use 1 1/2 meters.

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8 inch octagonal coil bottom view unepoxy.jpg
8 inch search coil attached in pvc and aluminum pipe handle.jpg
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