IGSL

[Davor]

That's about it. There is, however, a situation of abrupt phase change, as the ferrous and non-ferrous metals differ in their behaviour regarding orientation. So for example a small Croatian change, which is in fact shiny metal plated iron junk, gives non ferrous response when laying flat, while perpendicular position sounds ferrous, and while waving a coil approaching and departing coil over a coin laying flat gives ferrous response, and in a middle it gives non-ferrous sound. In effect such junk coin gives abrupt phase change and abrupt tone play. Same happens with other combinations of metals. It is more difficult to hide something this way.

[sukri01]

hi... does anyone here got igsl coil for sale? i'm making the first version igsl

[Davor]

It is not that complicated, so why don't you simply make it yourself?

[Davor]

BTW, I realised that I'm quite happy with discrimination settings fixed to both Fe and non-Fe just overlapping at foil (dual tone), so I'll be able to replace potentiometers with trimmers, and use the discrimination potentiometers for beach/dry land GB instead.

[sukri01]

i have made 2.. but performance is very bad.. just a few inches for a coin and shattering sound when i swing..

[Davor]

Shattering sound is most probably a consequence of "Disc threshold" trimmers cranked all the way. It turns U8a and u8b into a kind of slow recovering comparator, or worse if you used some opamp other than LM358. Most opamps are very unhappy if + and - inputs depart by more than 0.5V, and that's what happens when "Disc threshold" is cranked all the way.

[liekwang]

davor

?Hi can you please tell me what to put in the type of ic U1, U2, U5, U6, U7, U8, U12 I am confused I built a petravka the Board layout in page 22 please let me know

[Davor]

ICs as per schematic are OK. You can replace U5 and U6 with TL061 for lower consumption, or TL071 for a bit lower noise.
It is preferable to use 4u7 bipolar capacitors as indicated. There are some advantages in using bipolars over using back to back capacitors.
The largest capacitor (1000uF) was drawn opposite on my board, so please make sure to turn it properly if it is the case on your board as well.

It is advisable to make a pin-swap mod to make sure Fe channel works well. You may apply some other mods on the go.

[liekwang]

?Davor pin out 7808 get 9 volt not 8volt why not 8volt

[Davor]

Are you sure you didn't put 7809 by mistake? I'd be surprised to see 9V as output for 7808, but even that will not ruin anything ... provided you have good 12V source. The whole point of using 7808 instead of 7809 is that you have a little more headroom before the low battery problems become too annoying. Otherwise 9V would be just fine.

[liekwang]

?But it did not work at all and there is no sound coming out of speakers later try I check again because I was tired of my often fail to create metal detector but I made surf really well with his sensitive that I don't like to surf too much false signals

[Davor]

To get any sound out of IGSL (and in fact most of Tesoro descents) you need a working Tx oscillator. So if you want you device to start doing something, make sure your Tx coil is connected, and oscillator works, next see that you have -6V, and so on.

[liekwang]

?Hi I have davor respectively 6volt and 0volt voltage in rx and tx is it good

[Davor]

Depends where you have them. Does your Tx oscillate?

[Davor]

And now something completely different.

I was playing with phase shifters in order to have all metal phase reference (AMPR) for discrimination separated from GEB, and a GEB tuning range extended over somewhat more than 90° to include sea water. Well ... I got it. So far in simulation only.

I realised that things become simple if Tx/Rx phase offset is compensated to 0° prior to everything else. A proper 0° is tuned by means of a ferrite and GEB turned to the far left (ferrite) position at +90°. Zero degrees is tuned by means of a phase offset trimmer, and it also serves as fine tuning when swapping different coils. After true zero is tuned all other controls work as they should.

Next, I already have a nice +90° shifter on IGSL board, but I don't have a -90° source, yet there is another op amp (otherwise redundant) that may serve as inverter (-1 gain) and thus providing me with perfect complementary signal source.

To produce any phase in between, I need only 3 sources; -90°, 0°, and +90°. A simple potentiometer will do it smoothly and continuously.

To have meaningful discrimination, I need some symmetrical overlapping of ranges (+ and - 20°) and not exactly full 90° range. So I decided -20° to +70° is fine (and the mirror image of it).

GEB must run full course from +90° (ferrite) to somewhat below 0° (sea water), and this concept provides it. Full range can be sub-divided into 2 parts to go easier on a potentiometer.

It can be realised in "dead bug" technology, but perhaps a small perf board would make it neater. All outputs with names go to respective comparators.