Voodoo Main Discussion

[lamoiz]

Looking at the images for Fig. 3-17 and Fig. 3-20, it looks like external noise to me. The scope images in the book were captured indoors, and (as you can see) the preamp output is relatively clean. The noise on your board is extremely bad.

What do you see at the output of the preamp with the coil disconnected? Also try with only the damping resistor fitted (no coil).

here are the horrors ...

[lamoiz]

Looking at the images for Fig. 3-17 and Fig. 3-20, it looks like external noise to me. The scope images in the book were captured indoors, and (as you can see) the preamp output is relatively clean. The noise on your board is extremely bad.

What do you see at the output of the preamp with the coil disconnected? Also try with only the damping resistor fitted (no coil).

ok George, yes I have a lot of noise I will immediately measure without a coil to see

[Qiaozhi]

hi George, yes indeed my probe was 1: 1, tonight here is with 10: 1 probes. dc ..
[ATTACH]53855[/ATTACH][ATTACH]53856[/ATTACH][ATTACH]53857[/ATTACH][ATTACH]53858[/ATTACH]

Looking at the images for Fig. 3-17 and Fig. 3-20, it looks like external noise to me. The scope images in the book were captured indoors, and (as you can see) the preamp output is relatively clean. The noise on your board is extremely bad.

What do you see at the output of the preamp with the coil disconnected? Also try with only the damping resistor fitted (no coil).

[lamoiz]

hi George, yes indeed my probe was 1: 1, tonight here is with 10: 1 probes. dc ..

[surfdetector]

Hybrid mode

Well done. That looks good.
The extra ringing is occurring during the TX-on time, and does not affect correct operation of the detector. Fig. 2-1 shows the result for a Troy coil, so the Fisher F75 coil may quite possibly be different.

This is a very good project. I thank you George for all of your hard work in researching and developing it for us. Here is a link to one of my videos which shows the Hybrid operation towards the end:

https://youtu.be/6im66f8PGbk

[Qiaozhi]

Ok George ive given the best i can with what i know on points 1/ to 4/ - areas for further R&D on the final page 83 of your book.

Thanks Matt, much appreciated. That was the reason for the further R&D points, to make people think about possible improvements.
Although any chatter caused by alignment of the two channels was resolved to my satisfaction, there can still be instances where some dubious targets can break through. This also happens with VLF detectors, with some being worse than others. I presume that's what you're actually referring to in your discussion.

[Math]

When I was discussing chatter in the book, I was referring to some of the experimental prototype versions. At one point (page 10) I state: "Eventually after much effort, the noise, instability, chatter, and timing issues were all resolved."

Ok George ive given the best i can with what i know on points 1/ to 4/ - areas for further R&D on the final page 83 of your book.

[6666]

It's very difficult to get technical documentation 100% correct. I was reading an Arduino book recently, and discovered several errors. The book was published by a reputable publishing company, and their experienced proof readers still managed to miss stuff.

Its all good George.

[MartyJ1963]

Great work Alec! Looking forward to your upcoming video. I've had to take time out for a few days due to some serious repairs to the house that need to be done before Winter because it's already a little cold over here and they've forecast a colder Winter for Britain this year and maybe snow. I'm looking forward to the coil building stage though! Regards, Marty

[Qiaozhi]

hi friends i have pic18f452 can i use it for this machine

Not without modifying the source code to handle the differences and then re-compiling to generate a new hex file.

http://ww1.microchip.com/downloads/en/devicedoc/39647a.pdf

[Qiaozhi]

I have completed my build on the bench. I need to wait for some parts and then I shall box up the project and take it out for a spin. I shall post a short video tomorrow on my YouTube channel of the project operating in Hybrid mode. I have attached a picture from the Disc pre-amp output which appears somewhat different than in the book. I am getting about 8" on a George VI penny and about 5" on a US nickle. More tweaking is needed, currently I have all settings in default and I am using a F75 coil.

[ATTACH]53849[/ATTACH]

Well done. That looks good.
The extra ringing is occurring during the TX-on time, and does not affect correct operation of the detector. Fig. 2-1 shows the result for a Troy coil, so the Fisher F75 coil may quite possibly be different.

[Qiaozhi]

Hi George, the iron chatter you mention a couple of times in the book may be mostly eliminated using a '3rd channel' in software as "Disc minus Phase" here this should be Disc - PI channel then triple AND the 3 channels for the final output..
Ive used it successfully on a couple of projects it works well for the mismatched channel overlaps at crossovers.. usually big iron!

Hang on theres another bit of logic to go with that 3rd channel.. let me just check back..

When I was discussing chatter in the book, I was referring to some of the experimental prototype versions. At one point (page 10) I state: "Eventually after much effort, the noise, instability, chatter, and timing issues were all resolved."

[Qiaozhi]

Hi everyone . I was away yesterday, I had a car accident problem .... a girl and her cell phone smashed my car at a crossroads ... put my car in the trash .. *****.
Otherwise here are some pictures of the oscilo ..
[ATTACH]53841[/ATTACH]tp3 tp2
[ATTACH]53842[/ATTACH]tp5 tp2[ATTACH]53843[/ATTACH]tp6 tp3
[ATTACH]53844[/ATTACH]tp9 tp2
[ATTACH]53845[/ATTACH]tp10 tp3

a lot of noise on tp3 ..pff I don't know why ..

Sorry to hear about the car accident. Hopefully no-one was injured.

Firstly - switch your scope channels from AC coupling to DC.
Secondly - do you have your scope probes set to x10? The amplitudes of the signals are both about 10 times smaller than expected.

Please change the settings and re-post the images.

[surfdetector]

I have the beeps in pulse mode, very little in hybrid mode.
I tried outside, it's the same problem, I don't understand,
what do you think of the tp3 measure? there is a lot of osciliation after the impultion .. no ??

What does your coil flyback look like?

[sbalio1]

hi friends i have pic18f452 can i use it for this machine