TGSL Tuning & troubleshooting

[lunamay]

hi i've changed all ic's without lf353..i noticed same signal in speaker and my 7808 is crashed also..what should be next to check??

[Dennis the Mennis]

it seem that without simonbaker there is no life hier:P does anyone can help me or sugest something in my case?:P:P best regards to all

Hi Lunamay ,

Yes , I think everbody's taking advantage of -SB's break and there all having a week off or reparing their pcb's damaged by all the mods and tests , it's hard to keep up with all the test and hints .

(The schema I'm refering to is from TGSL rev.3 by -SB 08/18/2009)
For your pcb I would suggest first to remove IC U107 / LM358 ; this one should trigger the audio .
If your audiobeep is still there with U107 removed , then the audioproblem is somewhere around TR9/TR3/TR2 .

It is hard to predict what's more damaged with the powersupply wrongly connected ...

Do you have a scoop ?

If you have removed U107 and it stops , put U107 back in and remove U106 , work your way back like this in a logical manner

It is also a possibility that more ic's have been damaged ....

Otherwise you should remove all the ic's from your pcb , except the cd4024 with the TX coil connected !!! : this one is generating your negative voltage , and check if the positive - and negative voltages are there and on the correct places .

Then check the Tx and from there the Rx part by placing U101 , measure step by step everything with scoop while placing the ic's from the start to the end of schema .

Like I said it very hard to tell from a distance what's wrong with your pcb .
I hope these hints give a good start .

The attachment 'TGS compare' gives you a good idea what to expect on serveral testpoints.
Allthough it was made for the TGS ( not the TGSL , there are some 'minor' changes ) you should be able to 'translate' it back to the TGSL.
The TGS Compare 1.pdf was a compare between on original TGS by Molzar ( on the right side of the document ?) versus a homemade TGS by Max.

regards

Dennis the Mennis

[kuraja]

it seem that without simonbaker there is no life hier:P does anyone can help me or sugest something in my case?:P:P best regards to all

My guess is to check 7660, 7808 a few diodes there...I''m not sure if you have a diode connecting before the input of 7808. There is a reason people put those 1n4001 in front of everything....

[lunamay]

it seem that without simonbaker there is no life hier:P does anyone can help me or sugest something in my case?:P:P best regards to all

[lunamay]

hi
...i've got a great problem
when i was connecting my circuit for some mesurements i unfortunetly connected it like:+to - and _ to +;(

now my board is screaming from speaker
it's my foult and some foult of weather..it's wery hot..can you help me..it was a good board and worked not so bad..i just don't know where to search for bugs..please help

best regards

[Vladimir]

Perhaps at this point it is desirable to describe the reasons for the modification TGSL basic version.
1. (S1) In this position of coils in relation to the ground, the unit is very unstable with frequent peaks.

2. (S2) If the spire rising high above the ground. unit is also very noisy.

3. In the operating position in the movement of coils to the left and right, the unit occasionally have unforeseen and random peaks.

4. Bad sensitivity of basic units, less than 25cm for 1EUR coin.

This is my experience with the first version TGSL plate and coil DD27cm.

The first change I made in Tx, I got a variable gain entrance to the possibility of better sensitivity (in extreme cases up to 45cm in the air).
Resistors R25 and R26 I have replaced the recommendation of my friend, and got a little bit slower response unit, that I personally prefer.
R29, R31 values increased due to better gain filter, such an experience I had with certain models of devices that I previously made, and the diode D12, which in this part of the much better solution than 4148.

Finally with the increased sensitivity and increase the noise. I think that the appropriate filtering and some loss of sensitivity could be found a satisfactory compromise.
It remains me a lot more testing on the ground but the results are already very good.
Greeting

[mikebg]

, Theory never enough.

If the theory is not enough, then test the DC sensitivity and measure S/N ratio by a battery as signal source and voltage divider. The circuitry after demodulator should operate stabile.

[Vladimir]

According attached theory, your circuit is in stabile region because of very low frequency band.

, Theory never enough.

[dfbowers]

According attached theory, your circuit is in stabile region because of very low frequency band.

Nice document!

[mikebg]

According attached theory, your circuit is in stabile region because of very low frequency band.

[simonbaker]

Simonbaker
Thanks for the graphic analysis, a lot will help me in future work.

I think your mod is interesting. In some ways it would be good to move it all to a separate thread called "Vladimir Mods", because this thread is really for troubleshooting the standard TGSL with very minor mods. You can ask Qiaohzi to do it if you want.

Your mods make another version that may be well suited for deep detection. It is an interest I have had for some time.

I think maybe your 200K for R26, R25 is a little too high. Maybe 50K to 100K better, but real tests needed.

The zener diode for D12 is another interesting factor that is worth discussing later.

Regards,

-SB

[Vladimir]

Simonbaker
Thanks for the graphic analysis, a lot will help me in future work.

[Vladimir]

Vladimir, your capacitive load of opamp U105 creates instability. In theory it is avoided by a resistor as shown.

It should be so but, on the contrary, now is the device without peaks and a lot more stable. Is your opinion of theoretical or is it trying to practically?
In fact, I lost a few centimeters in depth, but given the stability.

[simonbaker]

Vladimir, your capacitive load of opamp U105 creates instability. In theory it is avoided by a resistor as shown.

I think that leading resistor is recommended also to make the circuit consistent for different chips. What values of R and C are best, is the question. Also, is this the best place to put this filter? And there should be a similar filter on the disc channel to keep them balanced, I think.

-SB

[simonbaker]

TGSL standard vs. Vladimir comparison, LTSpice

This is a circuit diagram with the changes about which I write.

I did a crude LTSpice comparison of the TGSL basic filtering, comparing the standard TGSL with Vladimir's modifications.

1. The top pic shows the Frequency response (Bode) plot comparing TGSL standard and Vladimir.

The green trace is TGSL standard.
The blue trace is Vladimir mod.

Note that the standard TGSL band center is about 8 to 9 Hz, Vladimir center is about 4 or 5 Hz. Vladimir gain is slightly lower, -1.7 db.

2. The middle pic is the response to a target (I made up the target waveform, may not be realistic).

The green trace is the TGSL standard.
The blue trace is Vladimir mod.
The red trace is the raw target signal.

Detection occurs when the response is above 0 volts.

Note that there is more delay (25 milliseconds) with the Vladimir mod, as expected with a slower response circuit. This would affect pinpointing. The detection pulse with Vladimir mod is wider (102 milliseconds vs. 70 ms), which is nice, makes longer audio beep.

Of course my reference target signal is probably not realistic, but it gives you a comparison.


3. The bottom pic shows the frequency response of each filter stage for Vladimir mod.

The green trace is the low-pass filter of R26/R25 - C15/C12.
The blue trace is the LM358 band-pass filter.
The red trace is the LM308 band-pass filter.
The cyan trace is all the stages combined.

I would note that not all the stages have the same center as the final stage. This may mean the combination is not quite optimally designed. It seems that the first stage low-pass filter is a little agressive, maybe that is the reason. However, if you look at the breakdown of the standard TGSL op amp stages (http://www.geotech1.com/forums/showp...&postcount=250), you see the centers are not well matched there. So Vladimir's mod is not any worse from that regard I think.

---------------

Conclusion: Vladimir mod looks like it achieves a slower responding TGSL, which may be better for deep targets, but more difficult pinpointing for shallow targets. The standard TGSL stages may also not be balanced as well as they should. Vladimir mod should give a slightly fatter audio beep. I would expect Vladimir mod may have less noise chatter, but can't really tell from this. Vladimir's gain is slightly lower (-1.7 db) than standard TGSL.

However, this is just theory. The MD must work well in practice. Only building and testing will say if a particular mod is useful. And of course different mods have different uses. Vladimir's mod may be what I want for dry sand beach hunting where objects go deep. Standard TGSL better for hard, mineralized soil, shallower targets, better pinpointing.

-SB