Experimental & Cheap VDI?

[Ham]

I have an idea for an experiment. What about connecting an analog meter with a potentiometer to the output of a metal detector's headphone jack? The meter indication would be controlled by it's own pot as well as the ac or dc output from the detector? This would "possibly' be a poor man's vdi. I would like to try the above but i just don't have the knowledge/experience in choosing the correct meter & pot? Any suggestions or is this a waste of time?

[Qiaozhi]

I have an idea for an experiment. What about connecting an analog meter with a potentiometer to the output of a metal detector's headphone jack? The meter indication would be controlled by it's own pot as well as the ac or dc output from the detector? This would "possibly' be a poor man's vdi. I would like to try the above but i just don't have the knowledge/experience in choosing the correct meter & pot? Any suggestions or is this a waste of time?

Unfortunately your idea will not provide a "poor man's" VDI.
The only thing the meter will display is the amplitude of the audio signal, and no target identification information will be provided.

[Ham]

The amplitude of the audio signal would be fine & give me a base line for experimentation. Any suggestions as to type of meter & pot (ohms) to try?

[Davor]

Amplitude measurement on its own is meaningless as the amplitude changes for a few decades just by waving a coil over a target. VDI devices establish a phase relationship between in-phase and quadrature signals via their ratio, which is theoretically constant over full dynamic range for a same sort of target.

[Carl-NC]

The amplitude of the audio signal would be fine & give me a base line for experimentation. Any suggestions as to type of meter & pot (ohms) to try?

Sorry, but this just isn't going to give you anything useful. Detectors back in the 70's used to do this, just so they could make the thing look more techie and charge more money. VDI is an entirely different animal, done on the internal signals before it becomes audio.

[scrungy_doolittle]

On the old whites DB4 the meter was essentially hooked to the speaker. It doesn't give any target information, but I have always preferred a meter to a tone. That said, what I would do would be to look at one of the classic whites schematics that are on this board (go to the schematic threads) and copy their meter. Essentially, you use a standard meterI think whites uses a 1 ma meter. I'm fuzzy on converting it to volts, seems like there is a resistor involved. You might just go to Radio shack, or ebay and get a simple analog volt meter, and hook it into your circuit. measure voltage.
VDI is a complex beast. I was hoping to ad vdi to the 4900, but ain't no way. However, I would like to find the schematic to the 4900. I looked at my 5900 and the vdi board is huge.

[WM6]

I have an idea for an experiment. What about connecting an analog meter with a potentiometer to the output of a metal detector's headphone jack? The meter indication would be controlled by it's own pot as well as the ac or dc output from the detector? This would "possibly' be a poor man's vdi. I would like to try the above but i just don't have the knowledge/experience in choosing the correct meter & pot? Any suggestions or is this a waste of time?

Seems there is no simple solution to this interesting analog meter VDI idea?

What our TTT say?

TTT=Think-Tank-Trust

[Davor]

One can make a simple enough VDI with a few comparators that would basically sort the targets into respective windows. Whites had a patent down that line (however obvious) and it can be done. My problem with every VDI is - to what end??? Beside looking purdy and largely useless, it uses extra resources ... just like any regular bimbo.

It would make a lot of sense if you have to make a machine that recognises quarters from dimes, but otherwise quite useless.

[Jose]

I would like to run a VDI for my GS4 home.
Objectives of different conductivity, create a well, which can determine the location of the GND control.
In fact, turning the GND Control until a null point of the signal, one can determine the degree of conductivity of the object, provided that the signal is not saturated.
However I do not think I've seen a pattern in the forum.
Regards, Jose

[WM6]

Beside looking purdy and largely useless, it uses extra resources ... just like any regular bimbo.

It would make a lot of sense if you have to make a machine that recognises quarters from dimes, but otherwise quite useless.

Sure, it is not usefull as exact and precise ID, but in first line as general info about target phase characteristic. One more informative source in acummulating experience about target characteristic info for bettter future decision about digging.

In this mean analog ID meter (as on old Whites 6000 DP SL - par example) is way more friendly as any present VDI display - cause it is more stable in pointing, than hectically changing digital numbers on modern LCD displays.

I consider such simple analog ID meter solution as welcome add to our VLF/IB design.

Whites (as well as Tesoro Toltec, Garrett M.Hunter 7, Compass BB, etc. ) is not simple for our implementation needs.

[Davor]

If you reduce your appetites ... it can get quite simple and frugal. So far I was not motivated to go any deeper in that direction. There is a straightforward phase detection if you go with a completely different signal path, but it will take me some time to get there.