TGSL troubleshooting questions

[Davor]

It does not say much because this pin is very sensitive to any kind of signal. What is the DC voltage at pin 7?

[ashefr10]

56 mV

[simonbaker]

Hello, since a few days my crackling same detector sensitivity minimum. the batteries are new. it occurs in all metal and discrimination. I changed all integrated circuits anything done. I check if the coil is not cut no problem either. thank you if you can help me.

Hi ashefr10:

Where are you testing? Indoors or outdoors away from any power lines, etc?

-SB

[ashefr10]

hello , hello, parasites are present mainly inside, the outside is no problem, even when with a little wet grass. I've had to change things a little so put a capacitor on the 220 k resistor on the noninverting input of the LF353, I also changed at this screen I covered the receiver part on the circuit board so part LF353 covered foil plasticized connected to ground. and since it is much more stable. I said that this is the version TGSL SMD. I am now trying to make the pro idx. I crafted the 2 double-D coils. therefore I still cabler, I will definitely need your help. In any case, thank you for everything. Are very competent people on this forum!

[zoomtronic]

Hi, I have assembled TGSL and now on first run i have nothing from speaker, it is dead... no sound On the pictures sockets are not populated with IC-s, those are pictures of ongoing buiding. I have 7.9v after 7808, and 0.802v on pin 4 of LM358 (u107b)

[zoomtronic]

My chopper didn't work, i fixed that, now i have problem with oscillator

[zoomtronic]

I fixed oscillator, it oscillates on 14KHz but can not null coils, i have 119mv on pin 7 of U101a
no matter what i do, move coils or turning them upside down it is still the savme 119mv, any idea?

[Davor]

Try playing with a small coin sized chip of a milk carton at various positions to find a deeper null

Once you find a spot, and it is placed somewhere on a coil body, simply attach it with some glue. By geometry (or a small piece of ferrite) you can null only the components at phase with Tx, but not those at angle. A small piece of foil does that, and the thinnest foil is found in multi-layered milk cartons.

[sini]

Dear friends,
I have question. How can I reach best result in nulling DD coil. I null DD coil only by overlapping Rx and Tx coils. Is the searching coil best nulled when on pin 7 of U101a is minimal voltage ? I can null coil (on pin 7 of U101a) to 10 mV. Is here any next nulling trick ? I made already 5 coils, but my maximal deep detection air distance is only 20 cm on 1 EUR. I will be satisfied, if I reach 30 cm air distance. Please, can you help me. Thanks, Robert

[Davor]

10mV on pin 7 is OK.
Regarding detection distance, do you get 20cm with or without chatters? Chatters are indication on a noise floor, and as it is very annoying with binary sound, detectors tend to be set for lower sensitivity or higher threshold to avoid chatters. If you can't experience chatters in the most sensitive position on Sens /thresh., you could use more gain in your system.
BTW, what chips do you use?

[zoomtronic]

the 119mv is constant, does not change at all, even if i put some metal or ferite object on coil or moving above coils, no sound produced from speaker.
Only sound is when i turning on device and turning off, and only then sound is coming from speaker

[dfbowers]

the 119mv is constant, does not change at all, even if i put some metal or ferite object on coil or moving above coils, no sound produced from speaker.
Only sound is when i turning on device and turning off, and only then sound is coming from speaker

Sounds like you have a very basic problem either with the way that you are measuring or with U101a. Do you have a scope? What happens if you measure the frequency at u101a pin 7? I just want to verify that you can see an amplified sinewave.

[zoomtronic]

I found mistake, rx cap 15n were damaged and shorted, now i have rx and tx, and it works. i have nulled coils not so good, i have 300mv on pin 7 but i have to build coil in housing so then i will null it properly , now i have 10 cm for Serbian 5 dinars - it is similar to 1 Eur.
Good for me for knowing electronics, this is no project for newbie , so many things to take care of. When i null coil, will test detector and give my judgment. $ now it looks promising

[sini]

Thank you, Davor.
20 cm maximal air detection distance is without chatters. More sensitivity cause audio oscillation ( periodic false detection ). I use IGSL with TGSL coil : Tx 5.7 mH, Rx 6.2 mH . Oscillation frequency is 14.8 kHz. Tomorrow I will play with threshold. I think I rebuild IGSL TGSL coil to IGSL Musketeer coil ( Musketeer coil should have better detection distance). Now I use chips same as described in IGSL schematic from Ivica with pin swap in Fe channel. Davor, please, can you explain me sentence: "By geometry (or a small piece of ferrite) you can null only the components at phase with Tx, but not those at angle". My nulling method is to find minimal residual voltage with proper 20 degree phase shift between Tx and Rx. Thanks

[Davor]

There are several things operating at angle, and it is good to know what is refereed to. We are talking about coil balance...

At a coil you have only Tx and Rx windings arranged to balance by geometry means. It reduces a so called "air signal" to a minimum. This signal is induced from Tx to Rx windings exactly as transformers do, but balanced in a way that it is at a minimum. In case Rx coil is not loaded at all, the "air signal" voltage would be exactly in phase with Tx voltage, or counterphase, but not at angle. Because of capacitive coupling etc. there is a very small component that is orthogonal to the Tx phase that appears at Rx coil, and it is a reason you can't achieve zero volts balance. At least not by squeezing and stretching the coils, playing with a curl of wire, or a piece of ferrite. All these methods are tuning the component of the "air signal" that is in phase with Tx.

You can introduce a piece of foil in vicinity of your coil, provoking induction of "air signal" that is at angle against Tx by means of eddy currents. Thin foil eddy current response is near ideal 90° so it is capable of nulling your coil deeper than achievable by stretching/squeezing alone.

The deepest minimum is a key to the rig sensitivity and stability, so it is important to get balance as deep as possible. The static phase is irrelevant for balance.

20° phase shift is a consequence of a loaded coil near resonance. a well balanced coil will remain well balanced regardless of the coil loading and the phase shift that changes with it. Because of loading, all responses are rotated by additional 20° or so, and it is only a function of resonance and loading - not balance. The 20° shift is relevant only for a waving ferrite response (e.g. ground balance).

A well balanced coil has the deepest minimum at any arbitrary angle.