Analog Target Indicator for VLF

[Nandor]

Thank you my friend , you gave me a very good idea about the log amps. I tried it and it works now!
Also tested some Us coins I have, Monticello Nickel 5.2 and US Dime 7 out of 10 .
Disc potentiometer is set to barely "touch" aluminium foil. Distance between the coil and the targets does not really effects vdi number, swept speed is more important.

I would like to find a proper housing for it and if possible a smaller new Meter. It would be nice to find something like Whites analog meter, this part is very important.
Also it has to be ampermeter or voltmeter? Maybe Carl can share some specs and info on the Whites meter.

regards

[Altra]

Great work! These retro circuits are interesting to study and build.

Have you hooked a digital volt meter to the output? It would give you ID numbers for each type of target. The Minelab Sovereign did this using a digital panel meter.

Thanks for posting


https://www.ebay.com/itm/40113909661...QAAOSwmtJXZVKh

[Nandor]

Thats a nice idea man. I have found a few Minelab ID meters on the net for sale. Would be interesting to see the schematic and the pcb and how it works.
For now I am happy with the needle meter .

best regards

[Carl-NC]

It would be nice to find something like Whites analog meter, this part is very important.
Also it has to be ampermeter or voltmeter? Maybe Carl can share some specs and info on the Whites meter.

It's a 1mA meter.

[dbanner]

Member Davor had designed this circuit a long while back. Thanks to him for posting his work.

[Nandor]

I can't figure it out . On the weekend I will try share another video and some pics with the probes connected to the test points.

regards!

[dbanner]

Analog 1mA meter is connected in parallel with circuit as voltmeter. Series trim resistor adjusts meter high end

20 led voltmeter in dot mode using two LM3914, perhaps could make a good display.

[Nandor]

It's almost ready to use, needs to be painted and mounted on my TGSL detector .

I used an old car relay for housing and made the front panel with laser a engraver.

[Nandor]

Just made another pcb for the IDX PRO and I discovered that there are errors in the new lay file that I posted earlier so after some corrections and modifications here is the corrected version.
IDX separates better nickel coins from silver coins than TGSL but hammered coins fall in the lower end of the meter like foil.

[Nandor]

Here is the schematic image with 8 oscilloscope shots of all the important test points. Target is 1 Euro coin distance is close and the coil is White's Blue Max 950.

regards

[dbanner]

Just made another pcb for the IDX PRO and I discovered that there are errors in the new lay file that I posted earlier so after some corrections and modifications here is the corrected version.
IDX separates better nickel coins from silver coins than TGSL but hammered coins fall in the lower end of the meter like foil.

Nandor, please recheck your PCB layout. Some things look strange, for example, the base legs of the two transistors are connected to different points. Is this as you intended? Also recheck the power supply rails.

[Nandor]

My bad ! Yes the bases must have to be connected to ground.
Thanks for telling me!

regards

[Nandor]

Here it is mounted on my TGSL.

It's a nice project.

[rajesh]

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.

[Op04]

Here it is mounted on my TGSL.
It's a nice project.

Incredible!! You did very good job... and Many thanks for the layout!