PI PROBE HELP

[daverave]

i want to make a wired probe like as used on goldscan machines...how do i go about making one ?????

[Jose]

What I did is recovering from an old TV a "Fly back"or high voltage transformer.
The core is removed, a length of about 2 or 3 cm is taken.
Then rolls enameled wire of 0.2 mm diameter (The wire diameter is not critical).
I do not remember how many laps, but check with the inductance meter to get an approximate value of uH 350.
You can connect a series resistance of about 10 ohms and parallel resistor high value if necessary to compensate for capacitance.
Just that, and experiment a bit to get the best performance.
Regards, José

[localbug]

I use an inductor found in cfl bulb, added a switch to swap coil and probe

[daverave]

i know very little about probes but i was looking at the goldscan schematic on this site and from i can see it uses a core which i guess could be a ferrite rod wrapped with the copper wire ???? should the inductance be the same as the search coil so easy to switch from one to another ???? does the probe need damping resistor ??? im very vague about probes !!!

[localbug]

My inductor inductance is 1.4mH yes its far from 350uH, but this is just a probe for me doesnt really matter if the performance less than the main coil performances. Beside the size significantly different I dont expect it to detect a quarter dollar at 30cm using a probe. As long as it works I feel happy. Yes we need the damping resistor... Use damping resistor that already installed for the main coil, unless if you plan to make both coil and probe active at the same time then you need another damping resistor for the probe. Just give it a try to see the result. Good luck Daverave

[kt315]

you may take a ferrite rod from any old chinese radio, so called low frequency and medium-frequency waves' antenna, LF MF ranges. do not know as to tell you about in english.
http://tech-edu.ru/sites/upload/hori...t90/t90-55.png

[daverave]

thanks guys for your answers...i have a ferrite rod which i use to use for setting up the ground control on my tesoro...maybe i will experiment with that and see what happens...not sure about the inductance that i need ??? or wire diameter ???

[kt315]

what I see at goldscan 4 schematic you mention the PP has high L and a resistor in serial. that means me an idea-conception of Eric to get smooth fall of the delta impulse,
he did experiment at last time of his life.
you may do or not to do such way, on your choice. in my opinion for your probe this is not important and 350-500 microH will be just optimal L.