Bipolar PI design

[ivconic]

I don't know if the problem is that I used 75HC4053 instead of 74HCT4053?
I don't think it should be any problem.

[eduardo1979]

Hi Ivconic.
I've recorded a new video.
Watch it at the link below.
https://www.youtube.com/watch?v=TKm-Gim7iC8&t=3s
My coil is 11 inches for GPX, and I've installed a 330 Ohm damping resistor. If the damping resistor isn't adequate, the detector won't discriminate. Pay close attention to the TX and RX cable connections and don't reverse them, because discrimination won't work either. Look carefully at the schematic. On mine, I marked them with numbers 1 and 2, and they should match. The frequency is 2 kHz and the delay is 10 uS. Carl's original circuit also discriminates between high- and low-conductivity metals by sound. Watch Carl's video and you'll see. The 74HC4053 isn't the problem, as you describe. The noise you hear in the speaker at low volume is due to the audio driver. I assume it needs to be improved a bit, but that's not the problem with the detector. The cable connecting the coil to the detector must be a stereo audio cable. I haven't protected the coil yet because I'd like to run more tests.

[pechkata]

Hello everyone
And no one showed a diagram of the pulses from the final transistors - why...?

[ivconic]

Hi Ivconic.
I've recorded a new video.
Watch it at the link below.
https://www.youtube.com/watch?v=TKm-Gim7iC8&t=3s
My coil is 11 inches for GPX, and I've installed a 330 Ohm damping resistor. If the damping resistor isn't adequate, the detector won't discriminate. Pay close attention to the TX and RX cable connections and don't reverse them, because discrimination won't work either. Look carefully at the schematic. On mine, I marked them with numbers 1 and 2, and they should match. The frequency is 2 kHz and the delay is 10 uS. Carl's original circuit also discriminates between high- and low-conductivity metals by sound. Watch Carl's video and you'll see. The 74HC4053 isn't the problem, as you describe. The noise you hear in the speaker at low volume is due to the audio driver. I assume it needs to be improved a bit, but that's not the problem with the detector. The cable connecting the coil to the detector must be a stereo audio cable. I haven't protected the coil yet because I'd like to run more tests.

Thanks Eduardo!
Your video shows 10-20% better air "depths" than my detector.
The diameters of the coils are similar.
As for damping; I looked at it on the oscilloscope and it looks perfect. Maybe I did something wrong.
It's possible that I didn't connect the coil to the pcb properly.

[ivconic]

I scrolled through the topic and found my post #190.
I watched the video from that post.
Hey! I did a good job and ported the code pretty well!
The only thing that needs to be fixed is the pulse width for the demodulators.
Piece of cake!

[ivconic]

Yes Eduardo, I always connected the coil wrongly compared to the connection from your schematic!

[eduardo1979]

Hi Ivconic.
I think it's great that you ported the Bipolar PI code to AVR. I'm not at all familiar with PICs. I've always worked with AVRs because I find them much simpler. Yesterday, I opened my TDI SL to measure the pulses with the oscilloscope to implement them in the Bipolar PI, and I think I accidentally shorted out the signal and burned the PIC. Honestly, I'm really sorry about what happened. I'm not familiar with PIC programming; in fact, I've never used MPlab, only Arduino. I'll see if I can find a solution; otherwise, I'll have to look for another detector.

[eduardo1979]

Hello everyone
And no one showed a diagram of the pulses from the final transistors - why...?

Hi Pechkata. No one showed the pulses because they were shown in the ITMD3 book. Everything is very well explained there. On page 448 is the time base for this detector: PCLK1, NCLK1, PLK2, NCLK2. Then there are the four demodulation pulses: TGTP, GNDP, TGTN, GNDN. I think that says it all. Those pulses match the schematic and PCB layout perfectly.

[pechkata]

Hello Eduardo
Thanks for the clarification.
But I wanted to see these pulses - on your boards.

[ivconic]

Hi Ivconic.
I think it's great that you ported the Bipolar PI code to AVR. I'm not at all familiar with PICs. I've always worked with AVRs because I find them much simpler. Yesterday, I opened my TDI SL to measure the pulses with the oscilloscope to implement them in the Bipolar PI, and I think I accidentally shorted out the signal and burned the PIC. Honestly, I'm really sorry about what happened. I'm not familiar with PIC programming; in fact, I've never used MPlab, only Arduino. I'll see if I can find a solution; otherwise, I'll have to look for another detector.

Provide me exact "pattern" of pulses You need from mcu and I will adjust in the code.
Also, if You are familiar with the code I posted; you can do it Yourself too, it's easy.
...
As for other questions about the problems I'm having with my detector; I tried a lot of things in the last hour.
First; the audio "buzz" has almost disappeared, it is heard only when the volume is at maximum, and even then it is very quiet, you have to listen hard to hear it.
Bypass cap on pin 7. at LM386 as well as Zobel network at the output solved it to a huge extent!
As for damping... 390 ohms is a good value for a given coil. Again I connected everything to the oscilloscope and checked with the damping "jig".
From approximately 380 ohms to 480 ohms, the damping is "PERFECT", the only thing that comes out of the RX front end "broadens" and "contracts" the RX signal a little bit.
Ok this is the first H-Bridge I'm trying to do the damping on, maybe I don't know how to do it right.
Currently I left 470 ohms on the pcb.
As for connecting the coil, I tried all possible "cross" combinations and still didn't get two audio sounds, especially for ferrous and especially for non ferrous. In all cases, audio behaves the same on all metals.
However, now in one position on the GEB trimmer, somewhere below 50%; I can find a "sweetspot" where the detector does not detect iron AT ALL... but unfortunately not even smaller colored targets, it only detects larger colored targets with a slightly reduced detection range (20-30% less).
I see that Carl has posted multiple versions.
I tried to make the last one.
But I haven't followed in detail (nor been able to find a list of changes in the versions); so it's possible I missed something.
Audio still does not differentiate between iron and non-ferrous metals.
That's the next problem to solve.
Summary:
Damping is PERFECT (if I understood everything correctly),
The coil cable is PERFECT, no doubt about it.

[ivconic]

Once I have solved all the problems on the existing pcb (if I ever do); I plan to draw a different pcb in the near future, with Atmega 328P, 4046 vco audio and I will try to make the pcb as small as possible.
Carl's pcb is "giant" and not convenient to install in smaller boxes.
But again, if we consider the box for the TDI, then Carl's pcb is of ideal dimensions.
This is the least important question.
I am currently interested in the distinction in audio between ferrous and non-ferrous metals and greater sensitivity to coins.
If I fail these two, then I have no plans to do anything further with this detector.
I will leave it in the workshop as an ideal platform for various experiments.

[eduardo1979]

Hi Ivconic. Please don't be discouraged. This detector works. You've seen my videos, and they're real. I'm sure you've overlooked something on your PCB without realizing it. In the video Carl posted, the detector differentiates the hue between high- and low-conductivity metals. I still don't understand your detector's situation. Look at my last schematic I posted a few days ago; maybe you'll find something useful. I'd love to help, since you're a wonderful person and I've always liked you. Could you show a photo of the oscilloscope, if possible, showing the damping results for your coil? I'd also like to see, if possible, a photo of the jumpers connecting the two RX inputs and the two TX outputs on your PCB?

[algan]

Hi Eduardo, I corrected the code in two versions, you can test if this affects the depth, one version is 80us and the other is 100us. the frequency potentiometer is no problem, the signal does not drop, you can increase the frequency potentiometer all the way.

[Carl-NC]

Audio still does not differentiate between iron and non-ferrous metals.

I don't understand why this is. If you rotate the GB pot fully to the Target channel, all targets should give a hi-lo response. If you rotate the GB pot fully to the Ground channel, all targets should give a lo-hi response.

[ivconic]

Uh then it's a misunderstanding Carl!
That's how it behaves.
But then there is no benefit from such behavior, is there?
Eduardo's video clearly shows that on iron it behaves like "wee-waa-wee" and on "non-ferrous" metals it does the opposite; "waa-wee-waa"... (however I may spell this onomatopoeia of sound behavior).
Regardless of the position of the GEB; you should always hear a different behavior of audio on iron than on non-ferrous metals.
What is the use of the fact that the audio will always behave the same on literally all metals, "this way" when GEB is at minimum and "that way" when GEB is at maximum?