REVERSE DISCRIMINATION

[daverave]

ok thanks kt

[Koala]

i got my mini scope today just got to build it....it only cost £15 uk pounds which is very good value...just got to find a box now with a window for the display...which will not be easy cause of size of pcb...i may build that disc circuit on verro board and experiment as you said.

Is it any good for normal diagnostic use. My CRT one affects a VLF detector badly. Take its this one link

[daverave]

the only problem with the mini scope is that it has only one channel which is not really good for setting up pi detector circuits....i use a hameg crt scope and i have no problem using it with metal detectors.

[Koala]

cheers I will get one cheap as chips anyhow. Loose a lot of depth with a Bandido if I leave my scope on. Auto adjusts the threshold level down in discrimination mode had a shock when gluing my coil up lost half my depth then remembered to turn the scope off. Same with the soldering iron luckily I am in the habit of switching it off each time I use it.

[daverave]

best of luck with that Koala

[Tim]

I would say a saltDD would work. Shielding would help. Once you have guesstimated these settings break out the scope and see if any/how much improvement. The only way to get the radical range is by placing a VR inline with the coil-only circuit, or having a vast array of coils, and a VR across the DDs. An inverted figure 8/double loop may also help with a PI if the coil is tuned and shielded right.
But I know FA- just ask here and they will tell you. My opinion is apparently not even worth proper scrutiny before being discarded and bagged.

[Tim]

Inverted 8 with VR at start and distance/size adjustment of inner circle. Reverse discrimination IS what I'm talking about here, As a quantitive measurement of variation as target moves through the combined field the relative conductivity may be measured.
Yep, I'm just full of sh*t. Ask Q he'll tell ya.
It was the corporates who had every bright idea and they deserve all the credit. The bloke who stuck the stick through the rock didn't invent the wheel, it was the marketing executive.

Little or no attention is paid to shielding until after the fact, when this compensation should be noted,calculated or considered prior to coil construction altogether. Especially regarding inverted 8s.
Just an old bushies ignorant opinion.

[daverave]

im not sure what i think about reverse discrimination...i guess some sort of meter is the way forward but in no way perfect.

[6666]

i just ordered the mini oscilloscope kit that you showed...i dont really have extra room in my surf pi housing for extra electronics for another sample circuit...so i will try the oscilloscope method but i will have to get a project box with a transparent window for the scope...not sure if i can a ready made one ???

Daverave did you ever get the oscilloscope kit
built ?

[daverave]

no i have not yet built the oscilloscope kit but i bought a mini oscilloscope from ebay and its working fine on my surf pi...the only problem i had was with the built in oscilloscope battery only being around 800 mAh cause the scope draws around 200 mAh from the battery...so im going to power the oscilloscope with a external li-ion 3.7v 18650 battery...just need a battery case which im wait ing for to arraive.

[6666]

Ok, what was the other one you bought ? and is it worth the trouble to add it to the surf ?

[daverave]

i bought a DSO 112 mini oscilloscope....i find it useful on tin cans and large items which show a large change on the scope waveform....apart from that it has limited use in my view.