TGSL Tuning & troubleshooting

[Davor]

Something like that.

There is one thing that makes me wonder... your coil is not fixed by any means, and you are experiencing these beeps when it gets nulled. Is it possible that your coil is picking some mechanical vibration, and because it being loose, and because of increased gain due to proper balance, your detector interprets it as perpetual beeping?

How about hot glueing your coils to some immobile thing, a plate or something?

[sdesic]

hot glue is still on it - glued to peace of foam board - removed part of it for last test (don't know how I will remove it when needed)
it is not mechanical ... I have left it for minutes gone away and it still beeps when it is nulled in that position

will try to trace signal from speaker to coils
any points that I need to check fist ?

[Davor]

Just follow it. Use a bit of intuition.

[sdesic]

TGSL EDU is quiet and responsive if I overlap coils more, detection is limited.
There is no sound until metal is introduced ...

that 50s delay is problem No1 ... and no notch No2... No3 is that over oscillation...
will be posting "scope" graphs tonight ... from speaker to front.

[Davor]

You don't have to post these, just find where this effect gets introduced.

Can you maybe observe a change in Tx amplitude modulated by this periodic beeps? If you can, just play with Tx operation point until this effect disappears.

[simonbaker]

Something always to consider -- where is your workshop where you are testing? Sometimes the EMI from power lines and house wiring can cause such beeping. A quick test is to take it somewhere away from all EMI and try to null it.

Also, try disconnecting the speaker and just monitor the speaker driving signal with an oscilloscope to see if you still get the beeping signals.

[sdesic]

Sound stage performs and has signal from metal on coil and from beeps

have signal on block 12 pin 5 of LM358
there is no graph in PDF file from Don to compare it ... both signals are there
moving on to next...

on pin2 LM393 don't have anything ... detectable by my "scope"

[sdesic]

Simon,

I will try that now ... two possible solutions...

[sdesic]

Started test without mini speaker ... with "scope" connected in place of speaker ... graphs shows beeps

Tried nulling in quiet enviroment - first method .. conected RX coil directly to voltmeter 2mV AC
detector starts to beep after (50s ?) even without RX coil ... even out of nulling position
problem in TX coil ?

with no coils connected there is no sound ...

[sdesic]

Can I reverse coils ?

[Davor]

You can, unless you connected one end of each coil to the shielding in a coil shell and potted everything in plastic. For that particular reason it is a good practice to do all such connections in a connector or a rig, but not in a coil. Once you pot everything in plastic it is done.

[dfbowers]

No sound when you disconnect Tx coil because the audio is the oscillator signal divided down. Also no oscillator means no -5V.
Not sure in anyone asked you yet, but when your audio starts beeping, does your 8V drop or is it fairly stable? I still can't help thinking that there is some sort of drain on your regulated 8V from the audio.
What would happen if you replace your speaker with an LED with a 1K resistor in series?

[sdesic]

Davor,

I will try reversing coils and report again, don't know why then we have basic coil wiring ground in head of coil presented in PDF documents.
It should be deleted from there ? Who is using that if it is not helping ?
I can replace my USB cable too - if it can help me.

Don,
thank you for your thoughts, will try that measurement. Soundcard scope can take 8V ? And other channel I will place audio so we can see.
Don't have experience with reading or using "scope"...

[sdesic]

Done testing with reversed coils ... with only RX connected as TX on PCB it starts to beep after 50s
with both coils connected reversed it is working with beeping on nulling position... if I overlap more it stops...
detects metal with less depth as it should

moving on

[sdesic]

Graph for 8V and speaker out signal with beeps going on "nulling position" of coils
8V has some fluctuations but I think it is there without scope connected - goes through GND and 22k + 22k resistor from other channel


it can be magnified


Don,
led is blinking allright, same like with speaker...
it is small speaker 1cm diameter ... like from PC internal modem