Sniffer XR-71 help

[Jafar]

green trace is the output of the LF365 at pin 6, and the yellow trace is the input of the LF357 at pin 2.
I still don’t understand what you mean by the ‘classical’ view.

Also, in my new board I’m using a 7812 to keep the voltage fixed at 12 V.”

[Jafar]

[kt315]

change the diodes back. no such suggestion to change 1N4148s on Shottky. not exist. you have to see 'classical' view on preamp output.

[pito]

[Carl-NC]

Please post a question only once, and in an appropriate thread.

In the case of the XR71, the diodes should clamp the signal to +E (+12V) so the signal at the input to the opamp should be limited to 12V +/- 1V, or 11V-13V.

[Jafar]

Hello, good time. Sorry if my question is unrelated to our previous topic, but I have a question about the clamp circuit used in the Sniffer XR‑71 device. At first, the diodes used in that circuit were 1N4148, but the circuit did not reduce the output going into the preamp to ±1 V. I replaced the diodes with 1N5819 Schottky types to solve the problem, but it still had no effect on the operation. Could you please guide me? Thank you.

[kt315]

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[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.

[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]

Milan

[kt315]

[kt315]

[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]

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

[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.