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I used a 7805 to prove out the problem/fix. I then installed a brand name 78L05. I wish you the best of luck. It took me nearly two weeks to sort that one out!
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My VooDoo is working.
For a coil I used an 8inch concentric I build for my HammerHead2.
This has TX & RX coils of around 400uH and has been nulled.
A 470nF film cap resonated the RX around 10kHz.Comment
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Hello!
I finally got the book and reading through it I noticed that at page 29 figure 3-3 shows a 47uF c26 electrolytic cap when it has to sustain both a positive and negative voltage, which changes depending on the position of the potentiometer.
When the voltage is positive the cap is connected backwards! Which obviously isn't a good thing!
Seeing as the caps already present are sufficient for the two tensions (+5v and -5v) a 100nF c26 not electrolytic cap should fix the problem.
I hope this can be useful to you
regards nixie.Comment
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Did you know that the null offset adjustment is very similar to the Hammerhead design, except that Voodoo uses a two-stage preamp?Originally posted by nixie View Post
It's only taken 15 years for anyone to notice that issue.
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Really? I've taken an interest in metaldetectors only recently so I may have noticed just because I wanted to better understand how they work. One day I would like to port it to arduino (stm32c103 bluepill) without changing the schematic, meaning I would just port the code you have kindly given to the bluepill and build a small costumized board. The bluepill costs only 2,50 Euros on ebay, 72mhz, adc 12bit with 3,3v and 0,6uS dual channel dma conversion! Resolution: 3,3V/4096! (check it out here: https://github.com/pingumacpenguin/STM32-O-Scope) Obviously this brings noticeables improvements, but I don't belive I would be able to project it by myself...
So now I'm trying to build Voodoo! What I don't understand is why so many designers use positive voltage as ground for the analogic circuit, to me it looks like everything would be easier with negative...Comment
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Hi NixieOriginally posted by nixie View Post
Strange that you mention the STM-O-Scope; I am just about start building one.Comment
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yes, a very interesting piece of code
on the other hand supported by an essential forum
(stm32duinoforum.com) with Roger Clark, mrburnette and many many more.
A place where you can truly learn.Comment
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Not all designs use positive ground for the analog circuit. Have a look at the Geotech Baracuda, and also Arduino Nano PI.Originally posted by nixie View Post
Geotech Baracuda - REV-A - Project Details
Arduino Nano Pulse Induction Metal Detector Project - Published March 2021
Note that those particular designs are using a PMOS device to switch the coil, whereas Hammerhead, Voodoo, Minipulse Plus, etc., are using an NMOS device, which means that the coil needs to be referenced to the positive rail.
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yes, I had already seen, but I don't understand what are the advantages of this choice....Comment
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If you take two typical examples: IRF9640 (PMOS) and IRF840 (NMOS), the former has a VDS of -200V, whereas the latter has a VDS 0f 500V. This means that the NMOS device can reach a much higher flyback voltage before going into avalanche mode, which generally results in being able to use a shorter main sample delay. NMOS devices also switch off faster and tend to have a lower output capacitance (Coss).Originally posted by nixie View PostComment
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What sort of depth / detecting distance are you getting with this coil?Originally posted by waltr View PostComment
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Originally posted by MartinB View Post
Have not yet gotten that far. So far got it working and Disc ferrous/ nonferrous.
The Hybrid display starts indicating with a US one cent at about 10cm. Don't have audio output connected.
This is not a great distance but I still need to tweak timing, etc.Comment
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Take the Voodoo schematic, label the battery-negative as ground, then re-label all the other voltage domains accordingly. See if that makes more sense.Originally posted by nixie View PostComment
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I blame Benjamin Franklin for causing the confusion between conventional current and electron flow.
He had a 50% chance of getting it right, and he chose the wrong option.
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