Voodoo Main Discussion

[lamoiz]

Are you getting noise type beeps or multiple target response?
If multiple target response is the problem your coils may be phased reverse.
Had that problem first trying my last coil.
Best

hi Godigit, to calibrate the voodoo, I used a tesoro spider.
they are not inversion beeps, they are beeps, even if there is no target on the coil. This happens in pulse mode, and really almost not in hybrid mode. I have checked all the measuring points, everything is ok .. I do not understand where it comes from. ??
Another subject, I changed r66 by a 180r, this one has not cooked, but it is still very hot ...
With the tesoro coil, the detection distance is very small .. cola can about 30cm and gold ring 5 cm .. it is very little anyway ..
I will try it outside, just to confirm that it is not a problem related to the environment of my workshop

[godigit1]

Here are the measurements, I used my adjustment potentiometer. the measurement on tp3.
[ATTACH]53811[/ATTACH][ATTACH]53812[/ATTACH]

but even now, the detector emits a lot of beep beep beep between each passage of target ...

Are you getting noise type beeps or multiple target response?
If multiple target response is the problem your coils may be phased reverse.
Had that problem first trying my last coil.
Best

[MartyJ1963]

Thanks George, Regards, Marty.

[Math]

FBS coils for Explorers/Etracs ive measured..

Standard coils..
The 10" slimline (in between the early 10.5" and later 11" pro)
TX @ 580uH/0.9R RX @ 510uH/5.7R

The 11" Pro coil.. TX @ 577uH/0.8R RX @ 514uH/5.3R

Aftermarket coils..
Detech 8x6" SEF.. TX @ 578uH/0.8R RX @ 517uH/5.0R

All closely matched and the RXs in these mutual DD setups
have an Fres of around 300 to 400khz

The FBS square TX drive has a very fast switchoff - not
dissimilar to a PI and produces 3-400khz size peaks like 'spikes'
on the RX thats used alone for detection.. like a line of miners swinging their picks
at the silver and gold.. if you wish to these coils tune well
around 25 to 30khz (to match the main freq set of the TX drive.. the PPS if you like)
This 'high vlf freq' giving good sensitivity to small low conductors..

Used untuned on a PI these allow a sub 10us sample delay on the RX second peak
when using a good 150 or 200V mosfet on a fully resonant drive 5x less capacitance
and no need for the diode it just adds lumps n bumps when trying to keep a
smooth flyback at these levels.. i dont like to hear those magic hammers banging around inside my machines ive heard enough of those thro the stones and my bones over the years
Gains are in the lower noise and faster sampling.. matched for finding those pennies from Heaven and we must keep in harmony with Eric and remember why and for whom he invented such wonderful detectors.. sure they were better designed for finding big things deep like snettisham hoards round circles and such.. I think he knows more than hes let on about the energies at these places..
Perhaps we should pause just for a minute to wonder why he chose 86hz over 100? and I think ive remembered correctly her name is Kathleen

[lamoiz]

I would have expected around 680R for the damping resistor, so that looks good.
The next thing to check is the main sample pulse alignment. See Fig. 3-19. If you try to sample too early, while the PI preamp output is still in saturation, the detector may become a bit jittery.

fig 3-19 tp3 tp 11 what do you think?

[Qiaozhi]

Here are the measurements, I used my adjustment potentiometer. the measurement on tp3.
[ATTACH]53811[/ATTACH][ATTACH]53812[/ATTACH]

but even now, the detector emits a lot of beep beep beep between each passage of target ...

I would have expected around 680R for the damping resistor, so that looks good.
The next thing to check is the main sample pulse alignment. See Fig. 3-19. If you try to sample too early, while the PI preamp output is still in saturation, the detector may become a bit jittery.

[lamoiz]

I would suggest concentrating on the Tesoro coil while you get the detector set up, as the default settings are good for that particular coil. Your damping resistor seems far too high to me. Check the PI preamp output on the scope and make sure that the coil is critically damped. Any under-damping may cause problems.
Also, get the PI mode working first before setting up hybrid mode.

Here are the measurements, I used my adjustment potentiometer. the measurement on tp3.


but even now, the detector emits a lot of beep beep beep between each passage of target ...

[Qiaozhi]

I just did the test with rx tesoro spider, 15.4mh and 22nf, it works, but .. I think the settings I made are not good. George, can you tell me what value to put to validate average settings?

Look at page 31, Fig. 3-21. This shows the alignment of the DISC sample pulse with the output of the DISC preamp. Adjustment of the DISC sample time can be done from the menu system.

I also have problems in the pulse mode, it works, but the voodoo emits constant beeps beeps between each passage of the target on the coil ... this also occurs in hybrid mode

See post #467

another question, where should we connect the shield ground?

The shield ground connects to battery positive, which is 0V.

[Qiaozhi]

hello everyone, this week I did several tests. I balanced the super d, no problem to do so, but the results on the display are not very good. I think the tuning is not yet set on my coil. (iron, non-ferrous). I also made a large size omega coil, in litz wire of 0.004 * 175 strand, damp @ 880r. it gets a delay at 10us. but then on the voodoo, it does not work at all ..... I do not understand!? I then connected a tesoro, the same as that of george's book. I have damper @ 1.5k, it works, but the voodoo is not stable at all .. I have not done the tesoro rx test ..

I would suggest concentrating on the Tesoro coil while you get the detector set up, as the default settings are good for that particular coil. Your damping resistor seems far too high to me. Check the PI preamp output on the scope and make sure that the coil is critically damped. Any under-damping may cause problems.
Also, get the PI mode working first before setting up hybrid mode.

[Qiaozhi]

George do you know anything of Eric Fosters PI discriminators.. the PPD1's?
After the C400 Deepscan they were early 80s i think and also housed in Arado 120 type enclosures with a similar centre zero meter for ferrous/non ferrous discrimination, auto silver foil rejection on sample delay? and ring pulls from gold rings by tone at low power settings. Apparently the meters worked well on the beach but could sometimes read non ferrous as ferrous on land
They had plastic oversize pipe stems that contained 8x D batts in the top section drawing only around 170mA ..good for the time! and very nicely handbuilt.
They used Garretts deepseeker type 8" co axial coil housings that contained tri planar concentrics I think
Inside the box there are 2 boards like Fisher 1265's ..power and PI circuitry on the bottom board with disc on top and the components are wonderful colours!
I have one named Eileen.. hand written on the board I assume by Eric.. I did get it running again its ~85pps same as the later Minipulses and with a large pulse width I remember around 250us
Its half reverse engineered and when Ive finished I plan to put the design up here..
TX circuitry I think is standard PI design and I will post up the coil values and Fres when i find my notes

That's interesting.
I don't know anything about the Eric Foster PI discriminators. Although I understand that Eric did experiment with balanced coils on PIs to provide ferrous/non-ferrous discrimination some years ago, but there were a lot of problems with ground effect in the same way as the old TR detectors.
Or is this an early version of the Goldscan / TDI circuits?

[Qiaozhi]

Ok thanks Qiaozhi i will get cracking!
Performances will vary largely depending on the coil used/built?
I use Explorer/Etrac FBS coils on my modified Minipulse..
I think the lower inductances, higher Fres/faster Rx makes them ideally suited for PI iron disc
Early used 10.5" and later 11" pro coils (with bust lugs) are plentiful and cheap
they can be had for 50GBP or less as can the smaller coils.. the 8" and Detechs 8x6 SEF which is a very good coil
I know these are all DD/~OO but i find the narrower detection zone better for target seperation..
Im not sure if this will apply to the Voodoo design being based mainly around concentric type coils?

What are the inductance values of these coils?

[Qiaozhi]

Thanks George,,,but what I wanted to know is would 208ma be enough to charge a battery pack or would I need one with more current output? I'm wanting to put a battery pack beneath the armcuff on my detector shaft and not in the same enclosure as the pcb,,so I can swap out battery packs in the field. Thanks, Marty.

You can see on page 90 that the 208mA is insufficient for the charger circuit shown in Appendix B, but you can alter that by changing the value of R1 according to the equations provided.

[lamoiz]

I just did the test with rx tesoro spider, 15.4mh and 22nf, it works, but .. I think the settings I made are not good. George, can you tell me what value to put to validate average settings?
I also have problems in the pulse mode, it works, but the voodoo emits constant beeps beeps between each passage of the target on the coil ... this also occurs in hybrid mode
another question, where should we connect the shield ground?

[lamoiz]

hello everyone, this week I did several tests. I balanced the super d, no problem to do so, but the results on the display are not very good. I think the tuning is not yet set on my coil. (iron, non-ferrous). I also made a large size omega coil, in litz wire of 0.004 * 175 strand, damp @ 880r. it gets a delay at 10us. but then on the voodoo, it does not work at all ..... I do not understand!? I then connected a tesoro, the same as that of george's book. I have damper @ 1.5k, it works, but the voodoo is not stable at all .. I have not done the tesoro rx test ..

[Math]

George do you know anything of Eric Fosters PI discriminators.. the PPD1's?
After the C400 Deepscan they were early 80s i think and also housed in Arado 120 type enclosures with a similar centre zero meter for ferrous/non ferrous discrimination, auto silver foil rejection on sample delay? and ring pulls from gold rings by tone at low power settings. Apparently the meters worked well on the beach but could sometimes read non ferrous as ferrous on land
They had plastic oversize pipe stems that contained 8x D batts in the top section drawing only around 170mA ..good for the time! and very nicely handbuilt.
They used Garretts deepseeker type 8" co axial coil housings that contained tri planar concentrics I think
Inside the box there are 2 boards like Fisher 1265's ..power and PI circuitry on the bottom board with disc on top and the components are wonderful colours!
I have one named Eileen.. hand written on the board I assume by Eric.. I did get it running again its ~85pps same as the later Minipulses and with a large pulse width I remember around 250us
Its half reverse engineered and when Ive finished I plan to put the design up here..
TX circuitry I think is standard PI design and I will post up the coil values and Fres when i find my notes