Beachmaster Files

[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

[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]

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]

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]

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

[Carl-NC]

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

[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]

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

[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

[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

[hamedtaran]

_As you can see,The voltage range of TP7 is from 2.5v to 4v
_Also, when I disconnect the pinpoint button, I have no any sense
_The sound frequency cannot be set lower than 800 Hz
Regards

[Olly]

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

Hi,

Are you saying that you can't adjust the threshold to a level where the audio output is not audible ?
Ideally RV5 should be a 20K pot, not 5K as too much gain here can lead to instability.
Normally you would start at the 20K setting and increase the gain if required. See section 3.9.2 of the build and test guide.

[Olly]

[ATTACH]57996[/ATTACH]

[ATTACH]57997[/ATTACH]

_As you can see,The voltage range of TP7 is from 2.5v to 4v
_Also, when I disconnect the pinpoint button, I have no any sense
_The sound frequency cannot be set lower than 800 Hz
Regards

If your nominal voltage at TP7 is a little high (Closer to 1.5V would be better) then moving the sample delay a little to the right (POT3) should solve this. See section 3.7.3 of the build and test guide.

Check the configuration of your pinpoint switch, it must be a normally closed pushbutton and in section 3.8.2 of the build and test guide I've shown a work-around if the pushbutton pinout is different (as mine was).

It's strange that you can't tune the audio frequency to below 800Hz, double check the values of R41(150K), RV6(100K) and C29(10nF).

Apart from a bit of fine tuning though it does look as though you've got the detector pretty much working, congratulations!
Kind regards

[hamedtaran]

Hi,

Are you saying that you can't adjust the threshold to a level where the audio output is not audible ?
Ideally RV5 should be a 20K pot, not 5K as too much gain here can lead to instability.
Normally you would start at the 20K setting and increase the gain if required. See section 3.9.2 of the build and test guide.

Hi, I bought RV5 from the bom file, it was 5k there. I will put 20k instead.

If your nominal voltage at TP7 is a little high (Closer to 1.5V would be better) then moving the sample delay a little to the right (POT3) should solve this. See section 3.7.3 of the build and test guide.

Check the configuration of your pinpoint switch, it must be a normally closed pushbutton and in section 3.8.2 of the build and test guide I've shown a work-around if the pushbutton pinout is different (as mine was).

It's strange that you can't tune the audio frequency to below 800Hz, double check the values of R41(150K), RV6(100K) and C29(10nF).

Apart from a bit of fine tuning though it does look as though you've got the detector pretty much working, congratulations!
Kind regards

Have you seen my test video? What do you think? Of course, the sound of the movie is a little weak, it is better to listen loudly
I connected these two pins together to test the circuit and it is working
see the picture below:



but there is a sound problem,Threshold sound is too much, I hope it will be fixed by replacing rv5
When I cut the connection between these two pins, the circuit no longer senses and produces a continuous sound

Thank you for your time, I will try again tomorrow

[Olly]

Hi, I bought RV5 from the bom file, it was 5k there. I will put 20k instead.

[ATTACH]57998[/ATTACH]




Have you seen my test video? What do you think? Of course, the sound of the movie is a little weak, it is better to listen loudly
I connected these two pins together to test the circuit and it is working
see the picture below:

[ATTACH]57999[/ATTACH]

but there is a sound problem,Threshold sound is too much, I hope it will be fixed by replacing rv5
When I cut the connection between these two pins, the circuit no longer senses and produces a continuous sound

Thank you for your time, I will try again tomorrow

Oops! My mistake...
My original design used a 5K pot, but then during testing I found that 20K gave better results so I updated the schematic but inadvertently forgot to update the BOM as well - I do apologise. I will update the BOM when I release the updated doc pack.

Pinpointing is only meant to be used for short periods of time (5 seconds or so at a time). When the pushbutton is pressed it stops updating the SAT level and holds it for a while allowing you to move over the target a lot slower in order to pinpoint the location. Unfortunately this level does leak away so pinpointing can't be used continuously in order to turn the detector into a non-motion type.

I have had a look at your video and it does seem to be working more or less correctly - I can't quite figure out the detection distance of the coin you are using but it looks reasonable. I found that with a 300uH, 20cm, shielded, bundle-wound coil and a TX width of 50uSec I was just about able to detect a 1Euro coin at 12" when the threshold was set low (more clockwise) in a low noise environment.

Kind regards