Beachmaster Files

[hamedtaran]

Hi

http://195.201.124.124:6677/35687519...9_19:27:53.mp4

The sound does not decrease, I set the threshold volume in the lowest mode, do you think the power is good?
I use 5k pot in rv5

[Olly]

Actually, the noise looks fairly uniform so a large portion of it will probably be filtered out by the integrators. Apart from that your waveform looks about right so I'd continue with the rest of the build. The EMI noise may give you a somewhat reduced sensitivity in your lab environment but it should still be testable and then in the field you'll probably be able to lower the threshold to improve the sensitivity.

Regards

[Carl-NC]

Then that is EMI you are picking up, it is not a problem with the detector circuitry.

[hamedtaran]

If you remove the coil do you still see the noise?

No, there is no noise when the coil is not connected

[Carl-NC]

If you remove the coil do you still see the noise?

[hamedtaran]

Noise pickup inside is pretty common. There are all sorts of electronic devices, power supplies, flourescent lights etc. which can generate unwanted noise. Try raising the coil above the floor by a few feet and keeping it away from any potential noise sources. It seems the main noise source is at around 65kHz which could be from a switching power supply. Try powering your board directly from 3 x LiIon batteries and see whether the noise improves. Wall-wart type power supplies are generally very noisy and not recommended as a power supply when testing metal detectors. The preamp gain is just over 1000x so it only takes 1mV pk-pk noise at the coil to give you the 1V pk-pk levels you are seeing.

560 Ohms is a good starting value for the damping resistor, but to get optimal performance you'll need to tune the value to your coil with a damping test jig as per the video link in the documentation. (After you've solved your noise problem)

Hi, I hope you are well, I couldn't solve the preamplifier noise problem, there seems to be a 200kHz noise. I assembled capacitors c26 and c37.



I used 3cell lithium battery

Regards

[Olly]

Hi, i placed 150pf capacitors, i use a 300uH 25cm coil and 560R for damping resistor. I placed the coil on the floor vertically

Noise pickup inside is pretty common. There are all sorts of electronic devices, power supplies, flourescent lights etc. which can generate unwanted noise. Try raising the coil above the floor by a few feet and keeping it away from any potential noise sources. It seems the main noise source is at around 65kHz which could be from a switching power supply. Try powering your board directly from 3 x LiIon batteries and see whether the noise improves. Wall-wart type power supplies are generally very noisy and not recommended as a power supply when testing metal detectors. The preamp gain is just over 1000x so it only takes 1mV pk-pk noise at the coil to give you the 1V pk-pk levels you are seeing.

560 Ohms is a good starting value for the damping resistor, but to get optimal performance you'll need to tune the value to your coil with a damping test jig as per the video link in the documentation. (After you've solved your noise problem)

[hamedtaran]

The signal is very noisy although the basic shape seems correct-ish...
Have you fitted C36 and C37 (150pF) directly on top of R10 and R16 as these help a lot in cleaning up noise picked up via the coil.
Also, what type of coil are you using and where is it located when doing these measurements?
I presume that you have fitted the correct value damping resistor for your coil (R6).

Kind regards

Hi, i placed 150pf capacitors, i use a 300uH 25cm coil and 560R for damping resistor. I placed the coil on the floor vertically

[Olly]

The signal is very noisy although the basic shape seems correct-ish...
Have you fitted C36 and C37 (150pF) directly on top of R10 and R16 as these help a lot in cleaning up noise picked up via the coil.
Also, what type of coil are you using and where is it located when doing these measurements?
I presume that you have fitted the correct value damping resistor for your coil (R6).

Kind regards

Hi, I fixed the problem of the voltage range in tp1 by replacing U1, now I have the following wave at the output of the preamplifier, which seems strange to me:

[ATTACH]57934[/ATTACH]

Kind Regards

[hamedtaran]

Hi,
It just doesn't make sense!
U1 has a 12V supply, but its output at Pin 4 (TP1) only appears to be swinging to 5.5V
The falling edge is also very slow, what kind of scope probe are you using and do you know its impedance?
Also, how confident are you in the accuracy of your scope's calibration? Does it show 12V when hooking up to your 12V power supply?

Did you manage to get a scope trace from U3, Pin 2 to confirm that it's running at 1 kHz and not periodically at a much higher frequency?

Apologies for all the questions but it's very important that each section is working as expected before moving on to the next.

Kind regards

Hi, I fixed the problem of the voltage range in tp1 by replacing U1, now I have the following wave at the output of the preamplifier, which seems strange to me:



Kind Regards

[hamedtaran]

Are the ICs all from the same supplier? If so, you may be replacing a fake with another fake.

No! , I want to replace another IC with a different manufacturer

[Qiaozhi]

I will replace the U1 IC again tomorrow, I feel that they are all fake,

Are the ICs all from the same supplier? If so, you may be replacing a fake with another fake.

[hamedtaran]

Hi,
It just doesn't make sense!
U1 has a 12V supply, but its output at Pin 4 (TP1) only appears to be swinging to 5.5V
The falling edge is also very slow, what kind of scope probe are you using and do you know its impedance?
Also, how confident are you in the accuracy of your scope's calibration? Does it show 12V when hooking up to your 12V power supply?

Did you manage to get a scope trace from U3, Pin 2 to confirm that it's running at 1 kHz and not periodically at a much higher frequency?

Apologies for all the questions but it's very important that each section is working as expected before moving on to the next.

Kind regards

you're welcome! I have to thank you for giving your design to people for free.
The frequency of U3 pin2 is 1KHz
My scope channels impedance is 1MΩ 25pF and I tested it with 1khz output on the device panel and there is no problem
I will replace the U1 IC again tomorrow, I feel that they are all fake, of course your opinion is important to me.
regards

[Olly]

Hi,
It just doesn't make sense!
U1 has a 12V supply, but its output at Pin 4 (TP1) only appears to be swinging to 5.5V
The falling edge is also very slow, what kind of scope probe are you using and do you know its impedance?
Also, how confident are you in the accuracy of your scope's calibration? Does it show 12V when hooking up to your 12V power supply?

Did you manage to get a scope trace from U3, Pin 2 to confirm that it's running at 1 kHz and not periodically at a much higher frequency?

Apologies for all the questions but it's very important that each section is working as expected before moving on to the next.

Kind regards

Hi
I test it again but:

[ATTACH]57908[/ATTACH]

[ATTACH]57909[/ATTACH]

About 5.5v pk-pk!

[hamedtaran]

Hmm, U3 may be running periodically in self-oscillation mode now, what does a scope trace at U3 Pin 2 look like ?
Also are you getting 12V pk-pk at TP1, (you previously had 5V). The full 12V swing is needed for the emitter-follower Mosfet driver Q1 and Q2 to work properly.

Hi
I test it again but:





About 5.5v pk-pk!