Voodoo Main Discussion

[Gunghouk]

Hi all, just to add to my previous post regarding ADC sampling.

The average value of a single sinewave cycle is zero. If you take enough samples during a single cycle which is most likely to give you the true value of zero, randomly timed or regularly timed samples for the same number of samples for each method ? The more samples you take the closer to the real average you can get.

From experience I can tell you the regular sampled time gives smoother, noise free results.

Opinions please

Cheers

Neil

[Gunghouk]

Hi all, I'm a recently retired automation engineer and have decided to return to the soldering iron as my retirement hobby/pastime and have started building the Voodoo (PCB version C and software 2.02) . Please let me say up front I have zero knowledge of detector technology but have some general observations regarding issues I have found so far. I apologise if some have been mentioned or resolved previously.

1. Regarding the Lt1054 - pin 7 and R48 should not be connected directly but be separated by a 100pf capacitor, as in the mini pulse plus detector, otherwise the voltage doubler doesn't work. An alternative solution I'm using, until I cut the pcb trace and fit 100pf, is to lift pin 7 from the ic socket. Of course this could just be this manufacturers device version (I've tried 2 of the same).

2. ADC averaging is far more effective at eliminating noise if the ADCs are sampled at a regular and precise timing interval such as in an interupt of sufficient high sampling rate. Sampling every program loop suffers from the vagaries of timing due to different pieces of code running each loop cycle. Think audio sampling at 41Khz etc.
I'm not sure what the ideal rate for Voodoo is but would like to ask if the 1mS TX rate interruot couldn't be used to sample all ADCs, all of the time, regardless of operating mode?

My 2 cents (so far).

Thanks George and Carl for a great project and for giving me a chance to revive my enthusiastism for electronics and my new found interest in metal detecting.

BTW I'm currently taking a long vacation in China and have been busy purchasing various detector PCBs from JLC while I've been here to feed my hobby upon my return to the UK. Obviously I won't need all of them (5 is minimum qty) so there could be some available in the New Year if anyone is interested. No guarantees on version no.s etc.

Looking forward to engaging in discussions on the Voodoo et Al.

Regards to all

Neil

[Qiaozhi]

Nope, Closed for EVER.

Yes, unfortunately that's true.
Andy told me that after 10 years of running the Silverdog shop, things have moved on and he no longer has the time.

[Sean_Goddard]

The PCBs are usually in stock at -> https://diydetector.co.uk/store/index.php
but I think the online shop is currently closed for holidays.
Otherwise, you can send the Gerber files to JLCPCB.

Nope, Closed for EVER.

[aft_72005]

For those who still want to make pcb; this is by now the latest version:

Hi ivconic

Thank you for this circuit and PCB design .
Are you built this project?

[Carl-NC]

Neither coil has a critical resistance requirement. I would use no smaller than 24AWG for the TX coil to keep the R reasonably low. The RX coil is in series with a 5.1k resistor so RX-R is even less important, use 30AWG if you like.

[m.shamim]

Thank you, but in the sixth chapter, nothing is mentioned about the resistance of the coil, inductance is mentioned, I am asking because it is not possible to buy loop Tesoro and Troy in our country, and I have to make the coil myself. I guess that the resistance The transmitter loop should be at least more than 4, but I don't know the resistance of the receiver to use the right wire

[Qiaozhi]

Hi everyone
I want to make a coil for a voodoo metal detector
What should be the resistance and inductance of each transmitter and receiver coil?

Read Chapter 6 - Coil Testing & Construction, and in particular look at Table 6-1.

[m.shamim]

Hi everyone
I want to make a coil for a voodoo metal detector
What should be the resistance and inductance of each transmitter and receiver coil?

[Levin]

thank you

[Qiaozhi]

Hello
I want to build a voodoo metal detector, are all the parts I need
currently still available?

There are no exotic parts used in the Voodoo Project. All the components should be readily available.

[Levin]

Hello
I want to build a voodoo metal detector, are all the parts I need
currently still available?

[Qiaozhi]

i have big problem with the system,it sense a ring in 5 cm..............please help me.

You will need to give more details than that.
5cm is only 1.96 inches, so you've clearly made a construction error.

Did you build the detector in stages and test each one before moving onto the next step?

[Sean_Goddard]

i have big problem with the system,it sense a ring in 5 cm..............please help me.

You would need to re-write the software and use a 18bit ADC or more. Switched gain in 3dB steps might also be an idea.

[m.shamim]

I don't have +5V value in tp15 In tp14 I have -5V One question: can the lt1054 copy with 50 mA output be the reason? Or there is another reason like 78l05

My problem was solved by programming the micro on the board itself
I failed to get the LT1054 to work with PICKIT2