Voodoo Main Discussion

[Qiaozhi]

After reading the contents of this forum with such a wealth of information with such friendly and supportive users for weeks and learning about various MD technologies, I have just encountered this amazing project, thank you Qiaozhi.

Having made my first prototype of Hammerhead version D on a home PCB which performs amazingly in air testing, thank you, Carl, yet to be tested in the wild, I was wondering if anyone had a couple of PCBs for the Voodoo. I am in the UK.

Thank you all,
Sean

I'm also in the UK, and I have a couple of spare blank Voodoo REV-C PCBs. One of them has a 40-pin socket for the PIC soldered in place.
Send me a PM.

[SeanS]

After reading the contents of this forum with such a wealth of information with such friendly and supportive users for weeks and learning about various MD technologies, I have just encountered this amazing project, thank you Qiaozhi.

Having made my first prototype of Hammerhead version D on a home PCB which performs amazingly in air testing, thank you, Carl, yet to be tested in the wild, I was wondering if anyone had a couple of PCBs for the Voodoo. I am in the UK.

Thank you all,
Sean

[phred01]

thanx for the link

[phred01]

Which country do you live in?

Australia

[Qiaozhi]

Hi all
Just become aware of this interesting project. Without having a batch of PCBs to be made has anyone one got for sale?

Which country do you live in?

[kt315]

DIYdetector is closed Where can one find Voodoo rev c gerber files be found?

you have to learn the forum deeply, IMHO The Voodoo Project - Published October 2020 - Geotech Forums (geotech1.com)

[phred01]

please repost hex file

[phred01]

The search for a PI detector that can discriminate against ferrous targets is like "black magic", so I chose "Voodoo".
It was almost called "Chimera", which arguably may have been more appropriate.

Voodoo is PIC-based, and source code is included.
If anyone is interested I can post the Gerber files, and ask Silverdog if he would like to add some PCBs to his online shop.
The design is through-hole to make it easier for DIYers.

Please do post the Gerber files or supply link to download

[phred01]

DIYdetector is closed Where can one find Voodoo rev c gerber files be found?

[phred01]

Hi all
Just become aware of this interesting project. Without having a batch of PCBs to be made has anyone one got for sale?

[Qiaozhi]

Thanks George. Fig 20 shows the +ve voltage doubler with no connection on 6(osc) or 7(Vout). So no sync used. That's why I lifted pin 7 to make it work but with sync still connected to pin 6.
Regards
Neil

Although Fig. 20 (+ve voltage doubler) does not specifically show the sync circuit, you can still add it as indicated in Fig. 12.

The converter definitely works as connected in the Voodoo schematic in Fig, 3-1, page 16 of the book. The only proviso is that the PIC needs to have been programmed, otherwise it definitely won't work since it's needs the sync pulses from the processor.

[Gunghouk]

Thanks George. Fig 20 shows the +ve voltage doubler with no connection on 6(osc) or 7(Vout). So no sync used. That's why I lifted pin 7 to make it work but with sync still connected to pin 6.
Regards
Neil

[Qiaozhi]

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).

The correct method (according to the datasheet) is the one used by Voodoo. See Fig. 12 -> https://www.ti.com/lit/ds/symlink/lt1054.pdf

The MiniPulse Plus design works slightly differently. The MPP TX pulse rate can be adjusted over quite a wide range, and the LT1054 does not function properly at the lower pulse rates, which makes it difficult to synchronize the voltage converter to the TX. Instead of attempting to use the TX to drive the LT1054 directly, it simply pulses the converter (via the OSC pin) to produce pseudo-synchronization.

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?

The Voodoo design is completely open-source, which means you are free to experiment and make improvements.

[Gunghouk]

Hi Carl thanks for the speedy reply. The TX interrupt of 1 ms would appear to be a suitable point to sample all ADCs and run the averages too. I'm going to play with that. There still appears to be jitter in hybrid mode so there's something else to investigate.
I give you credit in this project due to your software conversion to XC8 which allows nerds like me to use Mplabs X-IDE to tinker with the software.

The appeal of this project is not to make the best detector in the world but to improve, if possible, by sitting on the shoulders of giants like George, yourself and many others on this forum who provide the happily obsessed with technically challenging and thought provoking projects and which, ultimately, provide many enjoyable and fullfilling hours of entertainment.

Kudos

Neil

[Carl-NC]

Thanks George and Carl for a great project

Voodoo is 100% George.

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.

This is generally true. In the case of a Voodoo, the ADC is sampling relatively slow signals so I doubt the sampling jitter will make a big difference. I don't recall the processing loop rate of Voodoo so I can't say for sure.

My personal preference is to run the ADC at a specific sample rate (say, 5ms) and use the data ready to trigger an interrupt, whereby this sets the loop rate of the software. But then, I also run the timers for the TX & demods autonomously. Voodoo uses a low-end PIC micro so it is pretty limited for doing stuff like this.