Question about tgsl

[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?

[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]

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?

[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

[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]

-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?

[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.

[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.

[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]

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]

Well, I can tell you that winding coils to precise inductances requires some effort, and a jig to make things easier to keep count of those turns.
But knowing the effective parallel capacitance of the Colpitts oscillator, you can just bodge in a small value cap to tweak the resonance up or down as appropriate.
A better way of getting the resonances right is to start with Tx resonance as close to 14.5kHz, it doesn't have to be spot on, then adjusting the Rx resonance for the same spread (16.1-14.5=1.6kHz). The Rx resonance is easier to manipulate because it is just a parallel capacitor which can be adjusted up or down in value to get the right 1.6kHz spread. So if you end up with a Tx of say 14.4kHz then set the Rx resonance for 16kHz. The detector will function the same.

I have found that constructing a universal oscillator (coil tester circuit found here on forum) is very helpful when trying to set the Rx resonance. Just hook up the Rx coil to the coil tester circuit and scope the waveform while adjusting the Tank capacitance for the desired resonance. Having gotten the correct resonance, it is simply a matter of reconnecting the Rx coil to the metal detector circuit and putting in the correct capacitor value. This sort of approach obviates the need to keep removing the Tx coil from its oscillator.

Yea you are right I know that the difference between tx and rx resonance should be 1.6khz,I don't have any problem on how to get the right resonance for both coils. But before I go ahead and make the correct coils I'm wondering if the -5.6v on TR2 (B) is normal or not,it is related to the coils?

Also I did not mention that I didn't put diode (D5) on the board cuz I thought it will give some depth and I wanted to try that but I don't think this have to do with the no sound problem right?

[dbanner]

Well, I can tell you that winding coils to precise inductances requires some effort, and a jig to make things easier to keep count of those turns.
But knowing the effective parallel capacitance of the Colpitts oscillator, you can just bodge in a small value cap to tweak the resonance up or down as appropriate.
A better way of getting the resonances right is to start with Tx resonance as close to 14.5kHz, it doesn't have to be spot on, then adjusting the Rx resonance for the same spread (16.1-14.5=1.6kHz). The Rx resonance is easier to manipulate because it is just a parallel capacitor which can be adjusted up or down in value to get the right 1.6kHz spread. So if you end up with a Tx of say 14.4kHz then set the Rx resonance for 16kHz. The detector will function the same.

I have found that constructing a universal oscillator (coil tester circuit found here on forum) is very helpful when trying to set the Rx resonance. Just hook up the Rx coil to the coil tester circuit and scope the waveform while adjusting the Tank capacitance for the desired resonance. Having gotten the correct resonance, it is simply a matter of reconnecting the Rx coil to the metal detector circuit and putting in the correct capacitor value. This sort of approach obviates the need to keep removing the Tx coil from its oscillator.

[waleed]

Ok, progress.
TX frequency does not seem correct but the TX wave form shape does.
A single beep on power up is normal so seems circuits are now working.
The TX & RX coils plus GB adjustment must be correct to detect metal.
Do not worry about the audio section yet. You need to start at TX and work through the first circuits.

Next is to look at the gates of TR4 & TR5. Use the scope ch1 on TX oscillator look at the gates with scope channel 2.
These should be switching on in sync with TX and about 90 degrees over lap.

Now get the coils to the correct inductance. TX coil = 6.0mH and RX coil = 6.5mH so TX frequency is correct.
Go back to dbower's TGSL 101 pdf for coil building. His instructions work using the TX oscillator to adjust coil turns to get 14.5kHz on TX coil then 13.9kHz with the RX coil connected to the TX oscillator. It is this slight difference that is required for best detection and for the discrimination to work correctly.

Then with scope channel 1 on TX oscillator output look at the RX pre-amp output (U101 pin 7) with channel 2 of scope.
Adjust coil over lap to obtain a null at Pre-amp out and a phase shift of about 20 degrees.

This is a VERY Fiddly operation as the very slightest movement makes a huge difference in the RX null.

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?

[waltr]

Ok, progress.
TX frequency does not seem correct but the TX wave form shape does.
A single beep on power up is normal so seems circuits are now working.
The TX & RX coils plus GB adjustment must be correct to detect metal.
Do not worry about the audio section yet. You need to start at TX and work through the first circuits.

Next is to look at the gates of TR4 & TR5. Use the scope ch1 on TX oscillator look at the gates with scope channel 2.
These should be switching on in sync with TX and about 90 degrees over lap.

Now get the coils to the correct inductance. TX coil = 6.0mH and RX coil = 6.5mH so TX frequency is correct.
Go back to dbower's TGSL 101 pdf for coil building. His instructions work using the TX oscillator to adjust coil turns to get 14.5kHz on TX coil then 13.9kHz with the RX coil connected to the TX oscillator. It is this slight difference that is required for best detection and for the discrimination to work correctly.

Then with scope channel 1 on TX oscillator output look at the RX pre-amp output (U101 pin 7) with channel 2 of scope.
Adjust coil over lap to obtain a null at Pre-amp out and a phase shift of about 20 degrees.

This is a VERY Fiddly operation as the very slightest movement makes a huge difference in the RX null.

[waleed]

Hello there..well I have replaced the 4 transistors (tr1 try tr7 tr8 ) the right way (I'm not sure if their integrity is good or not tbh) and when i turned the device on it gave a single beeping and stopped (this happen every time I turn the device on) and I felt it will work well but when I pass a target on the coils nothing happen, I measured the tx oscillation and there was ac output on the oscilloscope but I think the frequency on tx is not correct (idk if this will cause the problem) , also I measured the negative voltage and it was -5.7v it's good I think, also I measured U100 pin6 and there was a clocking signal output on the oscilloscope but I think the period is not same as in the document one, and finally the thing which took my attention is that when I measured TR2 (base) the voltage was -5.6 and i think it should be almost 6 volt normally (when no targets on the coils).

I'll say it again I don't know how much exactly the coils inductance so maybe the resonance frequency of both is not correct, let's say tx coil resonance isn't 14.5khz (less or more) is this will make the device have no sound when target pass the coils? Or at least there should be a sound even if the resonance is not correct and it will effect the depth or the disc, right?

I have two doubts maybe the coils isn't made properly or I have an damaged transistor (maybe TR2 because of the -5.6v on the base).idk