Question about tgsl

[waltr]

Thanks waltr for those useful informations,now I will build a proper coils as in the document maybe I'll build the concentric one I'll make sure that they have the correct inductance, but I would ask what about the -5.6v one the base of TR2 it is because of the coils? Because I saw that it should be almost 6v when no target on the coils I'm right?

That is what dbower says in his TGSL 101 pdf. ~6V with no target and 0V with a target.
Look at the base of TR2 on the scope.

I never checked this on my TGSL so will try to remember to measure tonight.

Possible U107 is installed backwards or there is another problem. You can try removing U107
Until I measure this and post, continue with the checking of TR4 & TR5 switches, outputs of U102a & b. This can be done with any coil on the TX oscillator.

Removing D5 will not increase depth. It is to reduce the ON duty cycle to the audio, TR2 & TR3, to reduce power.
The summing of D3, D4, D5 produces short audio pulses.

[waleed]

That is what dbower says in his TGSL 101 pdf. ~6V with no target and 0V with a target.
Look at the base of TR2 on the scope.

I never checked this on my TGSL so will try to remember to measure tonight.

Possible U107 is installed backwards or there is another problem. You can try removing U107
Until I measure this and post, continue with the checking of TR4 & TR5 switches, outputs of U102a & b. This can be done with any coil on the TX oscillator.

Removing D5 will not increase depth. It is to reduce the ON duty cycle to the audio, TR2 & TR3, to reduce power.
The summing of D3, D4, D5 produces short audio pulses.

Thanks waltr,can you please measure the dc voltage on TR2 base when no target on the coils and tell me?,and I'll appreciate if u can plug the tx only and do some tests which should I achieve.

[waltr]

Yes, I will measure tonight after dinner (~2300 GMT) with and with out an RX coil.

I have made an in-line cable that can 'open' the RX coil. Was handy for testing.

I listed the next tests that can be done with Only the TX coil. They are the sampling switches from the phase shifting circuits.
Also can test the GB and Disc pots with scope per dbower's TGSL 101.

[dbanner]

-5.69V at the base of TR2 seems suspiciously close to the negative rail voltage of -5.7V that you measured. I assume you measured base of TR2 with reference to common ( battery negative). Check the tracks around the footprint of U107. No Rx coil should be the same as no target.

[waleed]

-5.69V at the base of TR2 seems suspiciously close to the negative rail voltage of -5.7V that you measured. I assume you measured base of TR2 with reference to common ( battery negative). Check the tracks around the footprint of U107. No Rx coil should be the same as no target.

Yea I measured it with reference to common battery..so should I present it on the oscilloscope on the ac settings? And see if I get the ~6v?

[waltr]

Ok, just measured Base of TR2 and it is -5.9V with RX coil and -6V without RX coil.

This makes TR2 OFF. TR2 does not start to turn on until the base goes above 0.6V so 0V to 06V is off.
The 0V dbower's states is a typo.

So all seems ok with that part of your TGSL.
Also, being that it does beep on power up indicates the comparators and audio circuits are working correctly.

[waleed]

Ok, just measured Base of TR2 and it is -5.9V with RX coil and -6V without RX coil.

This makes TR2 OFF. TR2 does not start to turn on until the base goes above 0.6V so 0V to 06V is off.
The 0V dbower's states is a typo.

So all seems ok with that part of your TGSL.
Also, being that it does beep on power up indicates the comparators and audio circuits are working correctly.

Good it is close to the -5.69v which I have got, well now I'll build the correct coils with the correct inductance to make sure their resonance is correct or at least the difference between them is 1.6khz, bear with me guys I really appreciate your help <3, anyway I'll be back and post feedback when I finish the coils

[waleed]

Hello again..well first I want to say that I didn't mention that I made the edu mod on the normal tgsl circuit that's why I didn't get any sound when I turned the device and moved a target on the coil, anyway I replaced everything back as original so it's a normal tgsl circuit without any mod,now when I turned the device on it started to detect metals but only like 15cm depth for a coin,but the problem is the device is beeping whenever I touch the USB cable or ground pot,

The coil is concentric as dbowers document, I have Tx=5.5mH and Rx=6.22mH, resonance for Tx about 15.18khz and Rx about 16.48khz,the difference between them is 1.3khz while it should be 1.6khz right?,anyway I need to change caps for both tx and rx to get the correct difference, also I didn't check for nulling (I just attached the coil and started to swap a coin on it) because I know the resonance for both coils is not correct, I just wanted to test the board.


I would ask two things;first is the 1.3khz difference between tx and rx would make the depth problem?
Second thing is what would cause the beeping problem when I touch the coil or the cable or ground pot?

[waltr]

More progress.
Yes, best to build without nods first and get it working.

Coil resonance difference is to be evaluated by comparing the TX oscillator to the output of the RX per-amp and with test targets (coins). What coin??? A 1 Euro can be detected at 25cm on the BEST TGSL/coils, getting 20cm is good.

If the coils are not epoxied completely ridget with absolutly NO MOVEMNET vbetween them then a slight touch will move them and you get a beep.

Also, without everything properly grounded (GB pot case) and shielded

[waleed]

More progress.
Yes, best to build without nods first and get it working.

Coil resonance difference is to be evaluated by comparing the TX oscillator to the output of the RX per-amp and with test targets (coins). What coin??? A 1 Euro can be detected at 25cm on the BEST TGSL/coils, getting 20cm is good.

If the coils are not epoxied completely ridget with absolutly NO MOVEMNET vbetween them then a slight touch will move them and you get a beep.

Also, without everything properly grounded (GB pot case) and shielded

Hey waltr thank for the reply..yes I didn't properly secure the coils even didn't put a glue on the tx coil only tape,and didn't shield the coils nor the cable is shielded or grounded same as ground pot, so that would cause the beeping problem?,and how would I ground the ground pot like connect a wire from the pot on the metal side to the negative battery voltage on the board?

And I believe the depth would be improved if I get the correct resonance for the coils and then get the right null right?

[waleed]

More progress.
Yes, best to build without nods first and get it working.

Coil resonance difference is to be evaluated by comparing the TX oscillator to the output of the RX per-amp and with test targets (coins). What coin??? A 1 Euro can be detected at 25cm on the BEST TGSL/coils, getting 20cm is good.

If the coils are not epoxied completely ridget with absolutly NO MOVEMNET vbetween them then a slight touch will move them and you get a beep.

Also, without everything properly grounded (GB pot case) and shielded

Hey waltr thank for the reply..yes I didn't properly secure the coils even didn't put a glue on the tx coil only tape,and didn't shield the coils nor the cable is shielded or grounded same as ground pot, so that would cause the beeping problem?,and how would I ground the ground pot like connect a wire from the pot on the metal side to the negative battery voltage on the board?

And I believe the depth would be improved if I get the correct resonance for the coils and then get the right null right?

[kt315]

in stage of testing 'on table' you do not need to shield nothing. your coil and pcb must not move.
just you begin to move a coil you must shield coil before. electrostatic field charge accumulates just in moving process in air.
in some time moment this charge has to be discharged - plus potencial on minus one (kilo-Volts, 10.000 Volts). then that gives impulse of influence and you get beep sound
in speaker.

[waleed]

in stage of testing 'on table' you do not need to shield nothing. your coil and pcb must not move.
just you begin to move a coil you must shield coil before. electrostatic field charge accumulates just in moving process in air.
in some time moment this charge has to be discharged - plus potencial on minus one (kilo-Volts, 10.000 Volts). then that gives impulse of influence and you get beep sound
in speaker.

Dam I just noticed your data joining and number of posts, it's just indicate the experience you have,nice.
Well I'll secure the coil and shield it and connect a shielding cable then I'll ground the pot. Will black when finish.

[dbanner]

The "off" resonances of your Tx and Rx coils must be correct, otherwise your phasing will be off and GB and disc will not be within the adjustment range of your pots.
This is why the spread is important, to keep the phasing at your null such that the Tx lags the Rx by about 20 degrees (opposite is true for DD)
The degree to which the Rx resonance differs from the Tx frequency determines the phasing, so keep this in mind.
In order to balance the concentric coil, first lock down the Rx at 16.1Khz
Then adjust the feedback for the deepest null. Don't bother too much about the Tx frequency at this stage, just null the Rx.
Finally, you tweak the tank capacitance of the Tx oscillator to get 14.5kHz.
At this point it remains to do the final nulling by moving around the extra loop from the bucking coil for the 20 degrees. It is more important at this stage to get the 20 degrees phasing rather than the deepest null.
Hope this helps.

[dbanner]

Luckily for you, because your Tx inductance is a bit low, the frequency is above 15kHz, so bringing it down only involves adding capacitance in parallel with the Tx coil.
For nulling, you may have to add or subtract from the feedback turns, but it would seem that you are pretty close since your coil is working somewhat from the get-go. If you want to leave the Rx where it is and just bring down the Tx by 1.6kHz, that should be ok too.
Read through dbowers thread on tgsl concentric coil.