Sniffer XR-71 help

[Jafar]

abnormal signal. huge. it is not limited by the diodes VD3 VD4. 'delta pulse' must be approx 2V P-P. not more.

I checked VD3 and VD4 on the board — they are functioning properly."

[Jafar]

Our mains electricity is 50 Hz. My device is currently operating at 346 Hz — should I change it?"

[Carl-NC]

your circuit is overloading by DC component on preamp output. Overloading Protection circuit works, T2 is open.
in normal mode Overloading Protection circuit must be turn off.

T2 and T3 are not for overload protection, they clamp the RC reset on D2A so that the timing delay begins when the preamp comes out of saturation, no matter what is loading the coil. I think there is something wrong, either with the transistors or with the RC.

Our mains electricity is 50 Hz. My device is currently operating at 346 Hz — should I change it?"

No, your mains frequency doesn't matter so 346 Hz is fine.

Jafar, I have not built this circuit so I will not be much help. But I will say it is a more difficult circuit than other projects and, if this is your first attempt at building a metal detector, there are easier options. For now, it is possible to proceed without using the T2 clamp, just leave R13 out and increase the Signal pot to get the right timing. You may need to increase C4 to get enough delay.

[Jafar]

T2 and T3 are not for overload protection, they clamp the RC reset on D2A so that the timing delay begins when the preamp comes out of saturation, no matter what is loading the coil. I think there is something wrong, either with the transistors or with the RC.



No, your mains frequency doesn't matter so 346 Hz is fine.

Jafar, I have not built this circuit so I will not be much help. But I will say it is a more difficult circuit than other projects and, if this is your first attempt at building a metal detector, there are easier options. For now, it is possible to proceed without using the T2 clamp, just leave R13 out and increase the Signal pot to get the right timing. You may need to increase C4 to get enough delay.

Thanks, Carl. I’m currently in the city — tonight I’ll replace the transistors and share the results.
I’ll also test the RC circuit and let you know what I find.
I know you haven’t worked directly on this circuit, but if you could roughly explain what the output of each IC should look like, I’ll try to fix them with effort and time — or I’ll ask other friends for help.
Carl, I’m not using this device for coin detection — I chose it because I want deep detection capability.

[algan]

Solder a new board, starting with the power supply first, then check the frequency and so on, step by step, you're just wasting your time with this, you won't be able to fix it, learn step by step.This detector is not one of the best for deep searching, because it also gives false signals. As you dig, the signal disappears. The other thing is that it recovers slowly, there is no speed of recovery, you need to make corrections to the scheme, but for a hobby and to learn, it is fine.

[Jafar]

After D1, D2, and D3 start working, which ICs should be checked next?
If you list them one by one, I’ll inspect and troubleshoot them step by step to get them working.

[Carl-NC]

I know you haven’t worked directly on this circuit, but if you could roughly explain what the output of each IC should look like, I’ll try to fix them with effort and time

That's the problem. The RC clamp and the offset feedbacks alters the waveform responses so I don't know exactly how they should look. I can roughly guess, but it doesn't take much error in guessing to create an invalid answer. What you need are some correct waveform plots to guide you, and I don't have those.

[Jafar]

That's the problem. The RC clamp and the offset feedbacks alters the waveform responses so I don't know exactly how they should look. I can roughly guess, but it doesn't take much error in guessing to create an invalid answer. What you need are some correct waveform plots to guide you, and I don't have those.

Maybe KT has them — if he or anyone else could kindly send some waveform images, I’d really appreciate it.
Karl, just briefly explain the role of each IC in the circuit and the order in which they should operate, so I can have a roadmap for continuing and troubleshooting.

[kt315]

T2 and T3 are not for overload protection, they clamp the RC reset on D2A so that the timing delay begins when the preamp comes out of saturation, no matter what is loading the coil. I think there is something wrong, either with the transistors or with the RC.

i told how this part works many times. on a target T2 and T3 are turn off, no reaction. just on BIG target or a target near coil - OVERLOADING - when 'delta pulse'
has smoothed plot, T3 begins turn up, opens (by negative level of the Delta Pulse). T2 also opens - far "they clamp the RC reset on D2A so that the timing delay begins when the preamp comes out of saturation" - they clamp the RC reset on D2A so FIRST SAMPLE is taken from the right on X axis, via moving to the right, where amplitude of Delta Pulse is more low (blue line on the pic). and yes, D5 comes out of saturation because no overload signal on its input, no overload signal on its output, SAT continues working in normal mode, no influence.
it is sure clear for me Overloading Circuit Protection from the saturation and working just fine. it is done FOR NORMAL WORK OF SAT because DP is very sensitive non-motion PI detector.

T2 T3 turn off both
T2 T3 turn up both

[kt315]

Maybe KT has them — if he or anyone else could kindly send some waveform images, I’d really appreciate it.
Karl, just briefly explain the role of each IC in the circuit and the order in which they should operate, so I can have a roadmap for continuing and troubleshooting.

Milan Karakas did. i did hope his site is still working, but not. i did not keep all images.

[kt315]

[kt315]

[kt315]

Milan

[Jafar]

Milan

KT, thank you for your kindness and help. I will follow your recommendations today.
Also, could you please specify what kind of waveform should appear at the outputs D4, D5, D6, and D7 when metal is detected, and when there is no metal?
If you clarify these, I’ll figure out the rest through practice and repetition.

[kt315]

no so sharp need to look the signals in DP. if you got a problem no one signal pic does not help you. be cause there not signal form is the cause of your trouble, but luck of technics and general unknowledge of electronics base. no practic? solder radio kits, solder any electronics kits from aliexpress.
DO ALL PCB AND GET STANDART SOUND REACTION ON METALLIC.
if you so need the theory of Pulse Induction, theoretic material, you can open ITMD in anytime and read the book. also I had recomended you read the article HAMMERHEAD PULSE INDUCTION METAL DETECTOR PROJECT, author CARL MORELAND.
best manual on all PI projects you seek around.