From: Dan D.
To: "GARY XX"
Subject: PI circuit board testing - Success - Many Thanks
Date: Mon, 26 May 2003 22:10:49 +0000
Hi Gary,
I found the problem. Your mention of the FET was it. I had substituted an
NTE312 which is supposed to be equivalent and it is except that the pin
configuration if different. so I installed a new FET and took a couple of
quik tests after I recalibrated the output of IC9 to 1 volt.
The circuit now detects a 1 ounce gold eagle at 21 inches and is very solid.
Barely detect is more like 25 inches so I am impressed. With some tweaking I
am sure I can improve it but if not it is still excellent.
I will be putting the unit into a aluminum box and mouting the coil in next
few days and will take a few pictures for your web site.
So many thanks and have a nice week.
Dan D.
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On Monday 26 May 2003 11:58 pm, you wrote:
Hi Dan, I'm not sure what your problem is or why you need to adjust it to
3.5 volts on pin 6 of IC9. But I would suspect you have a problem in the
circuit following it, The FET or the circuit around IC10 or IC11.
Additionally, Are all your supply voltages Correct?
(Within 10% of the -9.75, -5 and +5 volts that they shoul be)
Also, Does the VR2 Control work properly and adjust down to a Zero tone? It
Should.
Take care.....Gary
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From: Dan D.
To: "GARY XX"
Subject: Re: PI circuit board testing
Date: Mon, 26 May 2003 15:40:21 +0000
Hi Gary,
Thanks for the input. I think the caps are ok as I used the parts list
but I'll check them anyway. I figured I had a problem. Any suggestions
on what would make that voltage so high.
I'll send the pics when I get the circuit working. the coil is as I said.
thanks again for the inputs.
Best Regards, Dan D.
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On Saturday 24 May 2003 11:58 pm, you wrote:
Hi Dan, I don't have a coin like that so I can't comment as to if your 13
inches is good or bad! However The 3.5 volts on IC9 Tells me You DEFINATELY
have a Problem! The Most Sensitive operation occurs when this voltage is
between .25 volts and 1 volt.
Also, It was just pointed out to me today there is an Error on the Schematic.
Capacitors C11 and C12 have been reversed.
**This schematic has Just been Corrected today and reposted on my site.
Both the Parts List and Picture Overlay are correct, so if you built your
detector by those your Ok, but if you used the schematic, you need to check
those parts.
If these capacitors are not your problem, than something else is. For
ABSOLUTE SURE.
As to your Low Battery situation, This also tells me you have something
Wrong! But your detection field of 16 inches, is probably more like it
should be. I would be curious to see a closeup picture of your coil, If its
Possible!
Also a Picture of your completed unit would be nice. I would post the picture
of the detector on my site, if its OK with you.
My Email Address in on my Home Page, along with Important Instruction for
Emails being sent to me.
**************************************************************************
From: Dan D.
To: "GARY XX"
Subject: PI circuit board testing
Date: Sat, 24 May 2003 15:43:16 +0000
Hi Gary,
I have gotten the circuit working fairly well. The max detection range for a
one ounce gold eagle coin is 13 inches using a 15 inch coil. I would like to
know if this is ok or not very good.
I had to up the output of IC9 to 3.5 volts to get this detection range as
opposed to your recommended 1 volt output of IC9. I spend several weeks
playing with this circuit and I need to know if this is the maximum I can
expect out of it. ??
One interesting sidelight. when my battery gets low and and readjust the
IC9 to 1 volt and readjust the other pots I have gotten up to 16 inches
for the one ounce gold coin which I find rather anomolous. Do you have
any explaination for this?
Thanks for your help in advance.
Dan D.
**************************************************************************
Another guy just mailed me a board that he couldn't get to work properly.
Sympton: POOR SENSITIVITY, Particularly noticable on smaller objects.
Also a Low Meter Reading on all objects, Less than half scale maximum.
He had Previously built two units, so he knew how well this detector works,
Now he built 3 more, but in all three units None worked properly,
And he couldn't find the problem. Frustrated, he mailed one unit to me.
Looking the unit over and over for errors, and "Numerous hours" later I
finally found the problem. Not an Error, but a "Poor Batch of 2N3819 Fets".
This was very purplexing problem and totally unexpected. Most problems are
just minor errors or poor soldering connections.