TGSL Tuning & troubleshooting

[homefire]

LOL, Dang man. Just buy a DSO and get things done.

You can use it to monitor you heart when you find the first gold ring.!

[BKY1337]

I already know this thing and it has only one channel.
How can i use it to make my coil?

And which testpoints at the board should i use to connect it?

[Hyena]

Why not?

I build it for myself because im interested in it and i also want to save a bit of money. But im not an enthusiast like you and i think i will build maybe one more metal detector and then i wont need my oscilloscope anymore.

I still ned an answer to my question with the connectors. I want to try it and then i will see.
If it doesnt work then i will use my Multimeter or i will buy a dso and sell it after that but i saw that the dso are only 1 channel oscilloscopes.

I think i will need 2 channel for it.

Can i see the 20 degree lagging?

It might be caused by poor quality of my sound card, but I was not able to distinguish if phase shift is 20 or 200°, that bad it was. Just waste of time. I can imagine to use it for less then 1kHz to have 40 samples per wavelenght, but not more. Maybe you have some superb card and lots of free time to play. With about 4 samples per wavelenght quality was horrible.


Coil with 500-600g is good for 13". My 13" has 500g. No polystyren balls, only wire, epoxy and fiberglass for stiffness. It can easily break wooden stick in the woods


11" has only 200-250g. Light and stiff enough... I was aware of fragility of pure epoxy and I have good experience of fiberglass with epoxy on DIY compound bow limbs so I choosed to use it on coils. With fiberglass I can apply less epoxy and overall weight is also lower.

One channel - is better than no channel. You will see exact frequency, residual voltage and it is enougn. There is only 20 and 200°. If you have overlap, you have 20°, if you have underlap, you are on 200°. I can shoot short video on this in the evening... Also you can see if there is geb, dics with shape which it should have. Check frequencies CD4024 and so on. Better than nothing anyway.

[BKY1337]

Video would be nice. And is it possible to show me a picture of your 11 inch coil. My MD enclosures from Mikron Bulgaria are 27cm too. I hope i can make a 200g coil too. I have used glassfibers for my old coil and pure epoxy but my coil had 700g.

I made compound bow limbs too in the past :-D

I fear that the epoxy breaks when i only add the microballoons and maybe a block of polystyrene foam in the middle.

I can imagine that the resolution is very bad with only 4 samples.

Edit. I saw that my soundcard can handle up to 192khz 24bit output and 48 khz microphone. I cannot find the line in frequency.

[homefire]

Just monitor the output of the first Op Amp. No need to tie right to the coil.

[BKY1337]

Which one is the first?
U101a?

[homefire]

Yes. 101a Pin 7 to ground.

[BKY1337]

I tried it and i got only a bad wave. I could measure the frequency.
Maybe i need to adjust the settings or its just too bad for this.

I used a 470 and a 47k resistor to lower the voltage and i think it was 160mV at the microphone input from my netbook.
Maybe its too high for the microphone jack.

Edit: I tried it again and i saw that i need to adjust the time. Now i saw the waves, or better "spikes" . I have only 5 samples like Hyena. I think its not usable.

I saw that the Rx Signal is much lower.

[homefire]

That is what your looking for . Trying to NULL the Rx until a target is present. Try to get it down to a few Milli Volts Positive with No Target.

[BKY1337]

This was with my old coil which is already in epoxy. Ok thank you, i didnt knew this.
I think i will make my new coil with the multimeter.
I had 0,6-0,7 V at pin 7. But its not made properly.

Do you think its better to bring it to 0 V at Pin 5 from the other op amp?
Or is it the same?

[homefire]

Ground is always your Reference.

[BKY1337]

What?

[homefire]

All and any voltage reading you take will be referenced to 0 Volts or Ground.

[BKY1337]

Yes i know!

[dbanner]

If i remember correctly, when I built my first tgsl, I did not have a scope, so what I did to null coils was to put meter directly across Rx and adjust position for minimum induced voltage(null), then I connected Rx to circuit. Once i got it working, I adjusted it for maximum detection range(moving a variety of coins etc across coil), then I put GB trimmer at mid position and used small ferrite rod while adjusting trimmer until ferrite was not detected. I used a pc based scope which could also measure frequency of waveform, this is how I knew my TX was oscillating at correct freq. so I could calculate that my coil was correct inductance. You can also connect Rx coil to TX oscillator to check inductance of Rx coil. The inductances of coils are critical to proper functioning of circuit.