Help with mpp rev d

[Ogoun]

+5v TP2 = 5.05
-5v U8 Pin4 = -4.95
Check.
TP 1 Frequency ~ 1200
Pulse width 51us
Is this an issue?

R3 50us 0.5v


TP1 Pulse width 20us

[baum7154]

Tx ...Rx....Grnd
|____| ......|
|...............|
|--trimmer--|
|................|
| ...............|
to coil To coil


this way?

Some idea what went wrong? broken ic?
will post some pics of TP measurements tonight.
thx in advance

_____________________________________
If I understand your drawing then, Yes the trimmer should be from Ground to the 'HOT' side of the coil. Steps should be taken to insure that the trimmer cannot go below about 390 ohms or it will burn up the trimmer wiper contact. Take a look at BB Sailors white paper on "How to build a fast PI monocoil" on this site. In it he shows a good network for determining damping resistance.

Dan

[baum7154]

Here is the link to BB Sailors paper:

www.geotech1.com/pages/metdet/projects/fastcoils/FastCoil.pdf

[Ogoun]

Hy again,
build the coil from FastCoil.pdf
desoldered R1 (dampening resistor) and used this variable resistor setup from the pdf.
Something went wrong.
Can still detect a target, clear tone everything fine but like 3 seconds later i get a perma tone.
Maybe SAT is broken?
Put my Oszi at TP 9 and it swings from ~+2v to ~-2v although no metal is near coil.
Any advice?
Audio threshold VR doesnt change anything. DId i frie the Integretor? or VCO?
But why can i still "detect" something. Maybe SAT? ;/

[Ogoun]

Was a faulty pot connection
Another question :
Where do i measure "coil ringing"?
Output of opamp 1 right? U5 pin 1?
Because even with a dampening resistor < 200 there is no ringing at all.
Coil is 321/2.1 dont know cap. (i sticked to easy fast coil pdf)

x10 probe over resistor shows the same : nice spikes no ringing.
Hard to get the critical dampening.

[6666]

In theory as you adjust the coil damping it should look something like this animated gif.

http://www.geotech1.com/forums/attac...8&d=1341095735

[Ogoun]

Soldered a 100ohm resistor in series with a 5k variable resistor.
No matter how low i set it, just get the "last" picture from the gif.

Ill try it without any Resistor.
Maybe i wound the perfect coil

[baum7154]

Was a faulty pot connection
Another question :
Where do i measure "coil ringing"?
Output of opamp 1 right? U5 pin 1?
Because even with a dampening resistor < 200 there is no ringing at all.
Coil is 321/2.1 dont know cap. (i sticked to easy fast coil pdf)

x10 probe over resistor shows the same : nice spikes no ringing.
Hard to get the critical dampening.

__________________________________________

So can you set your scope so that you see just one pulse? The ringing should be just after that one pulse.

Dan

[surfdetector]

In theory as you adjust the coil damping it should look something like this animated gif.

http://www.geotech1.com/forums/attac...8&d=1341095735

This is a very good animation to illustrate the adjusting of the damping resistor