Super TGSL With H Bridge TX Diff RX Quad Sampling

[Silver Dollar]

"The coil is either completely out of balance, or you have some other problem there."

I'm using the 45T TX and 280T RX that's bifilar wound. This is the first time using those
so they are not nulled but looking at the signals I don't know how to proceed? Moving
them around does not change the output much. Is there too much TX getting to the RX?

I expected a different output! Here's a pic of the coils;



I'm not sure if I changed the caps in the preamp or not... I think we changed the 470pf to 68pf.

[Carl-NC]

Looks like there is way too much overlap.

[hoadlies]

HI,, SILVER-DOLLAR,,
I have been away for a while ,,But I see you are moving Onwards to coil connecting -Stage ..

YES -Nulling !!! I have now Built 4x DD coils & have now gotten the hang of the Nulling ,As DAVOR says you need to fix the coils to stop movement ..
What I have found is that after I tune the TX-coil for frequency with cap selection,, !![in the IDX case thats close to 6.6KHZ] this done from the unit fired-up ,I fix the TX in place temporally by Hot-Glue in maybe 6 or so spots .
I then lay the RX over the TX as you well know , & it is usually only about a 3/4'' gap -between the straight d/s leg's ,I then scope the Both for good sinewave , [I have only single scope,But ''STEVE-G/NUT ,showed me a way of using the exturnal feature & that works a treat -You can view each Coil by probing each TX & RX as long as you leave the time alone ]] .Then scope RX only to achieve a nil reading or minimum- reading [I probe the output of the Preamp for this..] .HOT glue the RX in spots but leave the straight D section for further-finer- adjustment , once close I then try fine-tuning the caps on RX . for the offset ,& the redo the Null .. for minimum output on RX [This is when the IDX is fired up]..
IAM-ONLY a Novice at this but have learned a lot from you members & many hours of practical coil building..my last coil came-out very good ..

LOOKIN-GOOD-MATE ,All the best with it ,,,,,,,,,,,,,,BARRY..

[Silver Dollar]

Well I disconnected the RX from the board and nulled it today. It now works in Disc mode but only has a range of 2"!
There are a couple of things on the board that are not to the schematic. I'll have to verify them and change them to
match. So a little bit of sucess!

[hoadlies]

Well I disconnected the RX from the board and nulled it today. It now works in Disc mode but only has a range of 2"!
There are a couple of things on the board that are not to the schematic. I'll have to verify them and change them to
match. So a little bit of sucess!

GOODONYA-MATE ,You will get there I am sure These things can frustrate us & all of a sudden we find our mistakes etc & alls well,But I realize you are Shooting in the Dark as its a new developement you are experimenting with..

I am currently building a DD for my ELCHEAPO CHINA M/D [GC1006] & so far its doubled its air-test ,I would like to know what it was copied from as its quite a good Board with lots of chips & transistors 5 pots analog meter etc....

I will keep playing with it for a while trying to tweek it some-where..

S/D did you have the TGSL running in STD mode ????? Prior to this new set-up ..

All the Best with-it MATE,,,,,,,,,,,,,,BARRY..

[Silver Dollar]

Yes I built it to stock settings before moding it. But now I have replaced 1/2 the board so
lots of places for mistakes. I thought of getting one of those Cheapo's and changing the
coil but now the real ones cost about the same as the Chinese ones so we don't bother...

[sinclairuser]

GOODONYA-MATE ,You will get there I am sure These things can frustrate us & all of a sudden we find our mistakes etc & alls well,But I realize you are Shooting in the Dark as its a new developement you are experimenting with..

I am currently building a DD for my ELCHEAPO CHINA M/D [GC1006] & so far its doubled its air-test ,I would like to know what it was copied from as its quite a good Board with lots of chips & transistors 5 pots analog meter etc....

I will keep playing with it for a while trying to tweek it some-where..

S/D did you have the TGSL running in STD mode ????? Prior to this new set-up ..

All the Best with-it MATE,,,,,,,,,,,,,,BARRY..

nice to see you back barry, told you the coil was the weak link on el cheapo china, a decent coil makes a lot of difference, my china board is good quality too, they really made an effort with it, shame they saw fit to put a standard 5" gold century coil on it, oh well much better now, i thought about putting the board in a dead cscope cs440 case, but i hated the look of it even more than the china, so i have upgraded the shaft to normal size specs(much stronger and no heavier).
ally.
p.s. dont forget to dump the original coil bolt (steel).

[hoadlies]

nice to see you back barry, told you the coil was the weak link on el cheapo china, a decent coil makes a lot of difference, my china board is good quality too, they really made an effort with it, shame they saw fit to put a standard 5" gold century coil on it, oh well much better now, i thought about putting the board in a dead cscope cs440 case, but i hated the look of it even more than the china, so i have upgraded the shaft to normal size specs(much stronger and no heavier).
ally.
p.s. dont forget to dump the original coil bolt (steel).

HI,, S/USER YES it was a good mod for the China unit [still open on my bench ] I found that by changing the TUNE-POT-from B50k to B10k [linear pot] improved the air test even further???? I tied going up to 100k it was worse the down to 10k & yes better ,The tune pot is supposed to balance the Coils??? to tune you hold button & centre the analog needle???..
'I feel theres a bit more to be gotten from it & it would be nice to have a SCHEMATIC of what it was copied from???

So far the air test is close to my IDX & it has great discrimination & ground balance !!!
CHEERS MATE take it Easy,,,,,,,,,,,,,,,BARRY..

[scrungy_doolittle]

I think the 3rd pulse duplcates the technique from the Whites patent, where they accept and look at a window centered on the sine wave, and about 2/3 the width. I think they refer to this as the "G" signal.

[scrungy_doolittle]

Try this.

Please enlighten me a bit. On U105, what is the purspose of the back to back diodes?

[scrungy_doolittle]

All of this grief with the opamps seems strange. I have a project that I want to kick off. Davor, and Silver Dollar, I would like you to be involved in it. Basically it will be a hybrid detector.
A potent microprocessor (I'm considering the PIC24FJ128G010 (about 6.50 in singles). This sucker has two amps, comparators, 3 different resolution A/D's and enough I/O to hand the rest. The idea is to generate the frequency from the microprocessor. I would like to take that square wave, and feed it into the balanced H bridge for a coil driver.
Ground balance, and discrimination are easy then. On the rising edge of the oscillator pulse, inside of processor, you start two timers running. One is set for a count to produce the necessary delay for the ground balance, the other is set for the necessary delay for discrimination. When they time out, drive a line high, and reload them with the width of the sample time. When that times out, drive the line low, and wait for the next timeout on the oscillator. This eliminates the problems with opamps trying to provide a timing pulse for the sampling. From there, the initial phase of development would simply use the rest of the analog processing, and bring the X,Y and G lines into ADC's for VDI.
OF course there is a lot more that can be done. The problem is that I don't understand the *function* of the remaining analog stuff. I would bet however, that much of it can be done in software. I would want the project to be open hardware/open software. My original idea was to start with the IDX pro, but the TGSL would also work I think.

I realize that Davor is in croatia, and that might make things harder. If I an get this started, I'll have to get some microprocessor PC boards laid out. Not to hard to get done, infact, I might just use some of the quick prototyping boards for these i.e. they do make circuit boards that have footpads for a 48 pin quad pack, and bring all leads out to stake pins. I don't know if you guys have any programming expertise, but I have almost 30 years of embedded programming under my belt. I believe that the PIC can be debugged and programmed with either the pickitII or pickit III (cheap interfaces). The programming software is free.
I was thinking originally about using an 8051 because I already have a bunch of boards that would work well, but the feature set on the Silabs 8050F040 is not quite as good as the pic 24 series. The plus is that I have boards with displays, and already have tons of code running on these. (They would be scrapped boards from the product I work on, with most of the non applicable parts removed.

P

[Davor]

Your problem with me is not my location, but my reluctance to mess with any micros. It is not that the micro can't be used even for a front-end, but the lengths you need to pass just to get there, and in my case a complete disgust with micros in a low noise environment of an amateur project. The very front end of a detector is best handled with pure analogue stuff, period.
Can it be done by a micro? Sure. To do it properly you should be able to sense the Tx coil's zero crossings and supply it with a corrected frequency - PLL-style. There is no need for extreme precision there, but so far such approach is not seen in any of the professional gears. You may supply it with a constant frequency, but you lose on power efficiency, and analogue solution proves better, again. Tx coil voltage is what matters.
Sampling Rx coil voltage by an ADC is also possible, but futile endeavour. What you need from a front-end are in-phase and quadrature synchronously demodulated components, as the rest of the magic happens on these. This magic can happen in analogue or digital world. Pick digital if you don't mind lugging lots of batteries. Or alternatively you may invest heavily to a digital part optimised for power consumption. Good luck with that.
And lastly, once you are finished with your design, so will be the lifecycle of your beloved micro. It happens more often than not.

If you look at what micros bring to the table, you'll see that it is mostly a way of obscuring your IP, human interface (bells and whistles) and precious little on top of that. Even multiple frequency gears can be realised in a manageable manner in analogue design, yet for some odd reason they are all designed with micros, and they all are battery hogs.

I'm considering making a dual frequency gear of my own with non-harmonic independent frequencies to avoid detection holes, active air signal cancellation, completely redone IF stage, and a completely different phase detector for direct VDI. All analogue. It can be done in a micro, but it would be very, very computation intensive. I'll take my time to do that, but I don't expect any of the commercial implementations in that direction by the time I'll finish it. Even by the template laid in this very paragraph. Why? Because commercial detectors operate under laws of marketing, and I don't.

[Silver Dollar]

I had some pcb's made to build an ARM M4 with Wolf chip to do something like the Xterra;


The processor can do the waveforms with DMA. And direct in and out for low mess and noise.
Maybe this winter I will start developing this board. I think it's easier to do analog but you
might be able to do some magic and see deeper with a good digital design. If nothing else
it's fun to play with!

http://www.geotech1.com/forums/showt...dec-Bare-PCB-s

[6666]

Please enlighten me a bit. On U105, what is the purspose of the back to back diodes?

You will have to ask Davor, its his schematic.

[Davor]

It is no mystery. I found that I like proportional audio much better than the common binary beepy response. Because in an intuitive soundspace the volume/depth relationship is too steep for linear law amplification of target responses (the 6th power etc.) I found that equalising the response by means of a log-compression works the best. Hence a diode compressor. As a bonus, I can tolerate more gain for the small signal so my dynamic range is wider.
I also kept a similar arrangement for gating, as it keeps the opamps out of saturation. Because all the opamps in a same package draw bias from the common circuitry, and they all share common rails, any saturation would affect all the opamps in a package, at least by introducing a delay after a saturation event. The overall response is dead on punctual with diodes, and I can easily discern multiple tergets.