Analog Target Indicator for VLF

[waltr]

Remember that the TGSL circuit uses a Comparator, U106a & b, to indicate a good target. It is only when both input to U106 are above the comparator's reference (sen. pot) that the audio is triggered. Iron targets will have either the GB or the Disc channels outputs of U104, U105, go lower.

If you are picking off the outputs of U104 & U105 to produce an analog signal to drive a meter, then both iron and non-iron will cause meter movement. Maybe you need to have a DC Bias to put the meter needle at center with No target. Then non-iron moves one direction and iron the other direction indicating positive and negative phase of the GB verse Disc channels.

Not sure how you would get "king of ground cancel' with this.

Another thought I have once circuit works:
The analog signal could also be an input to a audio VCO. Then there will be a varying audio tone indicating target types. Probably would want the audio out be gated with the comaprators (U106) so audio is quite with no target.

[Nandor]

Well the first thing I noticed is that there was no effect on the detectors sensibility with the test circuit connected to the comparator inputs without any buffer or pre amps.
The bias current is very important, I waved the indicator and the needle also moves and thats not how it should be working. Taking the needle in middle position would be also nice maybe it would be not affected by detector waving.
VCO is in my head also, with some window comparators or just a simple vco oscillator at the needles input. I have many ideas, just have to pick the working one.
I really want to make this project, it's really useful. When detecting with my friends Whites 6000 we have observed that coins almost every time are in middle or a bit higher position on the needle scale but sound is the same. Things that drive the needle up to maximum are mostly alu cans and other junks close to surface.
Back to my drawing board.

regards

[Melbeta]

Since you mentions the center deflection of the meter needle, back in the 1980s Compass first came out with the Good/Bad meter, called the X70 model. Now the next year they came out with the X80, and it was similar to the X70, but had the TID meter. I was curious, and I drew out the MSC circuit, which was the meter sending circuit, of both the X70 and the X80. But at that time, I was too busy to do more with it. I liked the Coin Magnum, which was a VLF that used discrimination that was NONE MOTION, and I thought that machine with the TID meter would be awesome. Yes, I would have like to stick in the TID meter into the Coin Magnum machine. And that is where it ended with me. Never went beyond that drawing comparing the two MSC circuits. Is this kind of interesting to you? Somewhere I think I still have that sheet stored somewhere in my things.
Melbeta

[Nandor]

I would be happy if you could share your drawings. Had some minor progress with this but not that much to be posted yet, been studying whites methods. Im stuck at iron signal overload and it still needs a circuit to detect phase difference.

regards

[dbanner]

Big bud pro schematic, coinscanner schematic, tesoro Toltec 100 schematic, are here on forum. Look to these for analog meter based VDI circuit different than White's. Especially the Toltec 100 which is easier to discern. The others are buried in the clutter of an overcrowded schematic drawing, not so easy to follow what's happening.
What about the CZ3/CZ5, didn't those have analog vdi metering circuits?

[dbanner]

I also have a schematic for a vco mod done with the Toltec by someone who posted a YouTube video. Seems to work very nice. If I remember correctly, there were two or maybe three distinct tones.

[dbanner]

Shouldn't it be a straightforward thing to add/ modify code to existing micro based VDI to instead drive an analog meter circuit.? A nice big analog meter to me is far better than a small 16x2. In the sunshine.

[Nandor]

I totally forget about Toltec ! Compass is really complicated, and never heard of Big Bud Pro. Thank you for the ideas, I have put it aside because of no progress. Been studying the discrimination of the TGSL to understand what to measure to get a proper arctangens with analog circuit. I have leared a lot, but still somethings are unclear.
Toltec has some special chip that makes this calculation if I remeber well anyways needs to be studied. Detecting with the Di pro 6000 SL is really cool and fun, I really like the VDI of it!

Digital is not my favorite, maybe the VDI of IDX Pro the original, because thats not with uPic. Eduardo shared a part of that schematic with the name of VDI LED and after he shared the original full schematic with LCD driver, thats also very interesting to study. It uses phase windows to compare the signal and that drives the specific part of the LCD.
Back to the basics

regards!

[dbanner]

Have you seen this. You can make the White's 5900di VDI. Eduardo did give all details.
https://www.geotech1.com/forums/show...ght=Analog+vdi

[dbanner]

Toltec uses the RC4200 analog multiplier chip, I like this solution as it cuts down on component needed to realize an analog vdi meter circuit. Stability ought to be excellent based on the datasheet.
There is however another chip, the Analog Devices AD534 analog multiplier/divider chip which is available and could possibly be the basis of a VDI meter circuit. I'm not sure.
Of course all this can be done using opamps and few components as is the case with the White's VDI circuit for the 5900/6000di. Notice on that particular circuit there's a dual transistor package no doubt to address errors due to temperature instability.
Here is the datasheet for the RC4200 and AD534.

[Nandor]

I have seen Eduardos topic, its very interesting for me. I have read it many time over, just started to understand how it works basically,but its a very big circuit as big as my TGSL board, too large to fit in the controlbox of my detector.
After taking some measurements with my scope it's easy to understand how discrimination works and how target identification should be made, ground effect cancelation is also possible. It needs ground balance because the Disc channel reacts to ferrite and the it moves the needle on my prototype. I was thinking about a circuit to measure the maximum aplitude of the Geb channel and if it exceeds a treshold level it should cut the voltage for the needle drive. I have observed that the Geb channel reacts very little to non ferrous metals, but if I wave a big iron object over the coil and it brakes the discrimination circuit than the amplitude of the Geb channel is way bigger than the amplitude of the Disc channel and they are also in phase. This is why I would like to make this circuit, the places I detect are agricultural lands and there are many iron components and parts from different machines .

Thank you for you time dbanner, regards!

[gurdal]

Hello to everyone,
Has anyone tested the circuit?

[Nandor]

Gurdal

Im really happy now, really! I havent made any progress with mine since 4 weeks almost, got stuck at a prototype working so so.
Thank you really much for this, as soon as I can, will make it.

best regards

[Nandor]

Looking at the schematic there are 2.2uF capacitors at the inputs, those must be polarized?

[Nandor]

I have built the pcb. Worked on the first sturt up but it cant make huge difference between colored metals and silver. Ferrous and non ferrous separation is working good. It's difficult to calibrate, somebody some ideas on calibration?