RELIC HAWK

[Max]

bulgarian RH schematic again

Hi,
I've spotted another difference between this (complete?) schematic and the bulgarian version called "relic hawk I", look at "f" point... that goes to pin1 of 4024...

don't you notice anything different ???

The 4024 gets its clock from geb/all-metal control signal, but in our RH schematic the "f" is at disc gate control signal...

So... someone could say... ok , it's always 5Khz there...

Sure... but I don't think is the same getting clock at 90° more or less ? Do you ?

In an extraordinary hi gain device...like THIS IS... that 90° could make lot of differences...

Kind regards,
Max

[Max]

Hi,
some wire arrived ...so I've made a new TX coil with 0.56mm diameter (bare) wire... and 3.5ohm resistance... to try if works now, with mods on transistors... and it works, I mean, oscillator runs good BUT this just using BC337, BC327 there.

(btw also my old 0.50mm coil works now with them in oscillator)

Unfortunately frequency I've got is not as required but lower... but this is unimportant in thoughts about oscillator startup.

So, the problem at oscillator we can consided as solved. So I'm updating schematic with new labels for transistors as required.

Here revision 1.8.

Kind regards,
Max

[Max]

Exactly correct. Since the output of the sample gate goes through a low-pass filter, the signal will be averaged over time. If the sample pulse is centered at the zero-crossing, then the result will be zero. Any metal that passes near the coil will cause a phase-shift that will produce an audio response.

Hi,
thanks for the answer, so I saw it right on the scope. What do you think of the broken beeps at higher distance ?

Could that be related to the odd shape of the coil ?

Kind regards,
Max

[Alexismex]

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Alexis

[Qiaozhi]

PS: Qiaozhi... about sampling at zero-crossing you mean that middle of control pulse must happen to be when rx signal is just zero-crossing, right ? Or do you mean something different ? I ask you cause the pulse is about 180° wide... so it's a bit complex to say where it is sampling...

Kind regards,
Max

Exactly correct. Since the output of the sample gate goes through a low-pass filter, the signal will be averaged over time. If the sample pulse is centered at the zero-crossing, then the result will be zero. Any metal that passes near the coil will cause a phase-shift that will produce an audio response.

[Max]

Qiaozhi read this...

Hi Qiaozhi and all,
today I tested again for alignment between rx coil and tx coil to get right behaviour from geb/disc stuff...

Now I'm doing this way...

I'm monitoring the RX signal at output of preamp, and at same time the control signal at geb and disc gates.

I found that the middle of control pulse for geb occours at zero-crossing of RX signal in a particular position: this I've found at geb pot cursor at middle.
In this position of RX coil I couldn't get minimal voltage, but detector still works all-metal as always, as well as disc-mode about range.

In this, same, position of RX coil I get , when knob of disc pot is about at middle the middle of control signal of disc gate exactly at signal minimum, at top of back sinus, just before signal rise again.

Following usual thoughts the geb sample at zero-crossing... the disc sample at peak (negative peak in my case) of signal... all as expected... so maybe this is the right positioning for rx coil ???

TX/RX phase shift is about 180° at this position.

The effects: on ferrite toroid I get a strange behaviour: at few distance, 2-3cm I get absolutely no signal... but at 10-12cm I get broken beeps, not random ones but due to ferrite, always!
Can detect e.g. copper good way... so seems good about this.
Iron stuff, similar to ferrite, is often ignored on short distance... but give broken beeps and cracking sound when higher... also 15cm and more from coil (this with an hammer head, pure soft iron).

So... disc somehow works... but bad. Why all this complication about it ???
Problem is that the beeps on ferrite and iron signal there's a problem there , but where ???

I have to say that my coil is not exactly flat at this time...but RX coil is somehow bounced over the large TX coil... thus the plane of RX is tilted of at least 3° from the plane of the bottom TX.

What do you think ? Must trash it and buy a coiltek ???

PS: Qiaozhi... about sampling at zero-crossing you mean that middle of control pulse must happen to be when rx signal is just zero-crossing, right ? Or do you mean something different ? I ask you cause the pulse is about 180° wide... so it's a bit complex to say where it is sampling...

Kind regards,
Max

[Max]

Hi,
still problems... with disc stuff... seems impossible to find a point where I can null iron!

Let me explain... I've made a number of tests changing the coil phase to look for the perfect balance of TX/RX phase to a value that will give the nulling on ferromagnetic component... till now nothing.

Now the stuff is even more interesting cause other stuff work... about as expected, but the dang disc still won't work.

I think this coil is a very critical piece... much more than others already made, something that need extreme care on details.

Kind regards,
Max

[Aziz]

Hi,

I don't like the huge resistor values for the opamp stages! The will produce much noises.
Don't forget to use polystyrene (styroflex) or polypropylene (WIMA FKP4, MKP4, ..) capacitors for integrators, differentiators, LC-osc. and so on.
If you can get, use polystyrene capacitors for critical stages.

[Fred]

actually i have just checked , and i found that i missed all posts before nº 125.
Sorry for all repeated posts i have made because of that..
Fred.

[Fred]

I already posted earlier, i dont have it anymore. Month ago i exchanged original RH pcb and few other things. Only photos left. That's why i can not check things...

Hi Ivconic,
Sorry i missed that post.
If you have good resolution photos it may help to clarify some points, but not enought...
Regards,
Fred.

[Max]

I already posted earlier, i dont have it anymore. Month ago i exchanged original RH pcb and few other things. Only photos left. That's why i can not check things...

Hi Ivconic,
not a problem now... device works both motion-no-motion, both all and disc about same detection range...just doesn't disc properly and exclude e.g. iron stuff...

Phase problem.

I checked the phase of disc control gate... it has range of 120°... so it's kind of "extended" disc... it's like ED120 of tesoro.

It's a good choice to me... cause it gives good compromise between disc and sensitivity to low conductive stuff, avoiding most of the iron.

Now the problem is...doesn't work, I mean with the coil I have!

I checked the coil and RX is 153° out of phase (when properly nulled) from TX signal...and seems no good to me.

Now that's the problem... we need a good coil to see it work....

Kind regards,
Max

[ivconic]

I already posted earlier, i dont have it anymore. Month ago i exchanged original RH pcb and few other things. Only photos left. That's why i can not check things...

[Fred]

Ok Max, thanks for info.
Maybe Ivconic can help with this if he checks his PCB...

Here i will install all the components i can untill i receive the ic´s.
Should not take too long now.

Regards,
Fred.

[Max]

Hi Max,
Yes if it is pure DC it will change nothing,but removing the 330R you can be sure that you don´t have some Ac that goes trhu the caps and somehow charges up at input.
You could also shunt pin 5&6 to ground and you will know if there is some internal opamp offset ...
regards,
Fred.

Hi Fred,
I've done the test... resoldered back the 10megaohm like in schematic, then disconnected the 330ohm and change nothing: always 85-90mV at output pin, so it's not ac signal that make things worse.

The offset of op amp I'm using is around 0.5mV, I've measured out of circuit.

Problem is that this offset voltage is amplified by the op amp... giving that 85-90mV offset boost at output.

Actually... I think at ML they put that trimpot just to compensate for offset... but the unexplainable is about schematics we have, probably all are incorrect.

Kind regards,
Max

[Fred]

Hi Max,
Yes if it is pure DC it will change nothing,but removing the 330R you can be sure that you don´t have some Ac that goes trhu the caps and somehow charges up at input.
You could also shunt pin 5&6 to ground and you will know if there is some internal opamp offset ...or bad grounding
regards,
Fred.