Beachmaster Files

[AK48]

"because as far as I know, using a large coil requires more pulse width."
from what you say: is it a constraint of physical law, I thought that any coil size could receive any pulse width but I also know that to go further and take more surface it is necessary to have a larger pulse width than for greater frequency for exemple for VLF, therefore to have a lower frequency so what about your opinion, explain to me
i'm still learning
thank you

[Teleno]

It's the inductance, not the size, although they're related.

For the same voltage a larger inductance takes longer to reach a given current.

But you can go around this by charging a second coil of the same inductance and as soon as it reaches the given current discharge it onto the first coil. Then you get an almost instantaneous charging of the first coil to the given current.

[hamedtaran]

"because as far as I know, using a large coil requires more pulse width."
from what you say: is it a constraint of physical law, I thought that any coil size could receive any pulse width but I also know that to go further and take more surface it is necessary to have a larger pulse width than for greater frequency for exemple for VLF, therefore to have a lower frequency so what about your opinion, explain to me
i'm still learning
thank you

I don't know the exact reason, because I made many circuits, I can say empirically that the larger the pulse width, the greater the depth and it can support larger coils, but this also has limitations, for example, more than 300 μs is not recommended and may cause errors. Okay, I'm sorry for my bad English

[hamedtaran]

I wish there was a video of the circuit working so we could understand how it works and how it's set up, currently there are only a few videos on YouTube that explain how to make it, but there are no other videos, I hope to see a video soon.

[Olly]

Hello, good time, my pcb order arrived from China
[ATTACH]57841[/ATTACH]
please design this circuit to be able to increase the pulse width up to 300 microseconds, because as far as I know, using a large coil requires more pulse width. How do you think pcbs quality?

Very nice looking boards.
If you increase resistor R3 from 47K to 200K then this should put you in the ballpark to getting a 300uSec pulse width.
Let me know how it works out as I haven't tried going above 75uSec.
Regards

[hamedtaran]

Very nice looking boards.
If you increase resistor R3 from 47K to 200K then this should put you in the ballpark to getting a 300uSec pulse width.
Let me know how it works out as I haven't tried going above 75uSec.
Regards

Thanks for the answer, more pulse width requires bigger capacitors, what do you think?

[waltr]

On a PI detect coil one needs to look at the CURRENT through the coil to determine if the pulse width is correct. Current through coil = Magnetic Flux.
Put a smallish resistor in series with the coil. I have used a 1 Ohm resistor.
Then put your scope across this resistor. The scope now displays current verse time (Ohm's Law I = E/R).
Run pulse circuit and look at scope wave form. The current will ramp up. If the pulse is long enough it will then level off meaning the current through the coil is constant. This is want we want, steady current before turn off current (end pulse).
Now you can determine if the pulse width is correct. Adjust width for the steady state. You want the magnetic filed in the target to the not changing when the coil field is turned off.

[Olly]

Thanks for the answer, more pulse width requires bigger capacitors, what do you think?

It all depends on what the DC resistance of your coil is and whether it flat-tops at 300uSec as Waltr has explained.

If for example your coil's DC resistance is around 3.2 ohms and it does flat top, then at 12V supply voltage you'll have a peak current of around 2.4A. (Assuming the series resistor is left at 1.8 ohms). The volt drop across the decoupling capacitor C5 can be roughly calculated according to I/C = dV/dT, or dV = I/C x dT.

Given I = 2.4A, C = 1000 uF and dT = 300uSec;
Then dV will be around 0.7V which should still be acceptable.
In practice this will be less as the flat-top current is not present for the entire 300uSec and the reservoir capacitor C15 also helps somewhat (albeit via R8.)

By the way George Overton's book, 'The Voodoo Project' contains an excellent investigation into the merits of flat-topping. (Appendix C on Pg. 93).
This book is well worth a read not only for the great project itself, but also for all the investigative nuggets of information it contains.

Kind regards

[hamedtaran]

Hi everybody, i don't have +12v in tp5 , i replace 5 ICs, But the highest voltage was 3v
I have attached a photo below:



Frequency of pin7 of lt1054 is 1033Hz
Frequency of pin2 of lt1054 is 1037Hz

[Olly]

Hi,

I can't quite make out the ploarity of the diodes from your photo. Check that D4 and D5 are fitted correctly and also check capacitor polarity (C13 & C14).
I presume that C12 has been replaced with a 0R resistor as per the text.
Could you send a scope trace of U3 Pin 2 and then also one from TP5.

Kind regards

Hi everybody, i don't have +12v in tp5 , i replace 5 ICs, But the highest voltage was 3v
I have attached a photo below:

[ATTACH]57875[/ATTACH]

Frequency of pin7 of lt1054 is 1033Hz
Frequency of pin2 of lt1054 is 1037Hz

[Olly]

One other thing, I see you have a power supply connector fitted.
Make sure that its voltage is 12V.

Hi,

I can't quite make out the ploarity of the diodes from your photo. Check that D4 and D5 are fitted correctly and also check capacitor polarity (C13 & C14).
I presume that C12 has been replaced with a 0R resistor as per the text.
Could you send a scope trace of U3 Pin 2 and then also one from TP5.

Kind regards

[hamedtaran]

One other thing, I see you have a power supply connector fitted.
Make sure that its voltage is 12V.

Hi, I checked all the parts you said, they are all correct, the supply voltage is 12V, tomorrow I will show you pin2 and tp5 on the oscilloscope.

[hamedtaran]

Hi,

I can't quite make out the ploarity of the diodes from your photo. Check that D4 and D5 are fitted correctly and also check capacitor polarity (C13 & C14).
I presume that C12 has been replaced with a 0R resistor as per the text.
Could you send a scope trace of U3 Pin 2 and then also one from TP5.

Kind regards

Hi

















Thanks

[Olly]

Hi,

Your traces seem somewhat odd!

Firstly, your TP1 has quite a slow falling edge and I can't make out what the voltage scale is.
It should look something like this: -


As you can see, the pulse amplitude is up to 12V with a nice fast falling edge.
Double-check all your solder connections on U1, especially its GND at Pin 7 and the decoupling cap C3.

Your signal at Pin 7 of U3 also has a really slow rising edge, this is what mine looks like: -


Again, a nice clean signal with fast edges. The voltage only goes up to a bit over 2V.
Double check that the value of R21 is 20K.

Finally, the output at Pin 2 of U3 should be a good 12V pk/pk square wave as follows: -


All of these traces should be measured with the scope GND lead attached to TP6.

Hi

[ATTACH]57878[/ATTACH]

[ATTACH]57879[/ATTACH]

[ATTACH]57880[/ATTACH]

[ATTACH]57881[/ATTACH]

[ATTACH]57882[/ATTACH]

[ATTACH]57883[/ATTACH]

[ATTACH]57884[/ATTACH]

[ATTACH]57885[/ATTACH]

Thanks

[hamedtaran]

Firstly, your TP1 has quite a slow falling edge and I can't make out what the voltage scale is.

I checked all the parts, I used two 10k resistors instead of R21, the value of c3 is correct, about 91nf, do you think U1 could be defective?