felezjoo PI(the best pulse induction metal detector that I made until now)

[jladre]

You can also hardly seen a 5x5mm soda can wall if you are just using a simple spider wave, flat spiral or any simple coil. You must work a 2 sizes coil and combine them to be one.

[freso]

Hi i see that you have eXperience ... Can i use electrolityc capacitors instead of tantal ones since i cant find them.... And can i use 5822 instead of 5819 diode .... And can i use 50 volts capacitors it's hard to find sole voltages ... Thanx in advence

[jladre]

Hi i see that you have eXperience ... Can i use electrolityc capacitors instead of tantal ones since i cant find them.... And can i use 5822 instead of 5819 diode .... And can i use 50 volts capacitors it's hard to find sole voltages ... Thanx in advence

You can use electrolytic cap, you can use 50 volts, you cannot use 5822 because it is 3amp it will burn your 7812. You can use any fast diode that has 1.5 volts rating with appropriate voltage rating..i think you can use even 1 amp rating like 1n4001..

[6666]

You can also hardly seen a 5x5mm soda can wall if you are just using a simple spider wave, flat spiral or any simple coil. You must work a 2 sizes coil and combine them to be one.

Would it be possible for you to draw a simple picture of the coil you describe here in this post to detect 5x5mm soda can, and like in your video, is it like in post #400 ?? thanks.

[jladre]

Would it be possible for you to draw a simple picture of the coil you describe here in this post to detect 5x5mm soda can, and like in your video, is it like in post #400 ?? thanks.

much likely like that coil..

[ivconic]

...It seems that your PC scope is having a problem sync'ing because there are gaps in the transmission, presumably because the processor is busy doing something else, such as updating the display...

Later i discovered the source of problem; the probes!
"Leaking" all the way! Useless!
I am waiting pair of new ones.
...
Say...neat work! Congrats!
I guess it's about the coil as reason why you can't detect soda can cut more than that.

"...It's simply some sort of conductivity discrimination based on sampling around the decay curve..."

Most probably is.
But try this; use small thin iron nail as target and some larger non-fe mass, and test detector on those with same adjustments.
See what will happen. (again this may depend on coil specs)

[Qiaozhi]

As far as I can ascertain, the detector continuously changes the sample delay, not just at switch-on, by checking when the preamp comes out of saturation. You can see this yourself by placing the coil near some metal, and then displaying the delay setting by pressing the Down button.

I've thought a bit more about this ... and it appears that the minimum sample delay is set automatically at switch-on, and can also be reset by pressing the Down button. It is not being continuously monitored. So it is important to hold the coil away from the ground and any metal when you turn it on. If you hold a coin near the coil and press the Down button, the sample delay gets stuck at a high value (such as 45) and then you a lose lot of depth.

[Qiaozhi]

I wonder how fast two LF357 would be in a 2-stage preamp ?, and thats handy to know if you cannot get a LF357, thanks.

That thought has crossed my mind as well.

[eclipse]

AD744 and OPA637 are fine replacements, tested them both work fine.

[Qiaozhi]

Hi Qiaozhi
A few thoughts come to mind from your post #867;
If the discrimination is based on the target decay or time constant curve then a minimum delay of around 16us would delay the first curve sample past undesired signal excursions that could greatly affect the beginning of the curve. As you suggested for strong target returns the software could monitor for the flat opamp saturation voltage to end; then delay a bit more to take the first curve sample. After that further samples would provide the overall curve shape to be evaluated for a match or cutoff with software stored curves.
Have a good day,
Chet

That could be one solution, but I'm wondering whether there's another possibility.
This detector is claimed to have the ability to reject mineralized ground. If it's using the same subtraction method as White's TDI, then it could also reject small iron targets (like the TDI). However, I wonder if it could also have a third (much later) sample pulse used specifically for rejecting ferrous targets. Since it appears to reject the Earth field quite effectively, there may actually be 4 sample pulses in this design:

1. Main sample
2. Ground sample
3. Ferrous sample
4. Earth field sample

This would explain the results I'm seeing so far. Also, since this is a non-motion detector, the processor would be able to capture the samples, perform the calculations, generate audio, and still have time to update the LCD without struggling too hard. Tests certainly infer that ferrous rejection is based on a number of samples, as the rejection is not perfect, and varies with distance from the coil and how you move the target around. In fact, often you can place a small target close to the coil with a poor response, and then move it around. When you again move the target closer, the response is improved. This must be telling us something about the way the target is processed by the software.

[Qiaozhi]

But try this; use small thin iron nail as target and some larger non-fe mass, and test detector on those with same adjustments.
See what will happen. (again this may depend on coil specs)

Thanks for the tip. I will try that later.

[dragomir]

I do not know but in samples with different antennas I found a very interesting effect. This instrument with a special antenna can capture the human biofield. By 60 cm. Captures my hand.

[jladre]

I do not know but in samples with different antennas I found a very interesting effect. This instrument with a special antenna can capture the human biofield. By 60 cm. Captures my hand.

It's normal for sensetive antena. It will detect the ferrous presence in your blood. Also your hand capacitance will make your machine to produce noise.

[freso]

thanx for help i have 4007 and it's the same as 4001 will use that and see

[Davor]

Not in my catalogue.