RELIC HAWK

[Fred]

Max,
I agree too that this connection doens´t make much sense, but if you connect the pot where you say the 6k8 resistor makes no sense either.

Regards,
Fred.

[Fred]

Hi Fred,
Very nice pcb you had made.How do you make it?

Hi,
I used double sided presensibilized PCB , UV and regular etching .?
But i didn´t made the clearance around non-grounded pins on the layout software, so i made this after with a drill bit.
Regards,
Fed.

[Max]

Max,
I agree too that this connection doens´t make much sense, but if you connect the pot where you say the 6k8 resistor makes no sense either.

Regards,
Fred.

Hi,
yes, you read my thoughts... but problem is then, if we wanna keep output near GND level, with trimpot connected as in schematic, we need extraordinary low offset op amp... something I cannot recall about ic employed in RH... that's the tricky part of this...

The pot as in schematic could be explained just considering extremely low input offset... that could lead to wanted/expected output voltage at U8 pin7, that, from what we know, couldn't be in real , originals RHs.

How to explain the 6K8 ? I really don't know... I could explain it and existing connection of trimpot but with very "special" device at U8.

Kind regards,
Max

[Fred]

Hi Max,
All OK,
If you disconnect the 330R resistor coming to pin6 of U8 (via 470nF caps), do you still get your offset voltages? if so it may be some coupling , or that the u9 3/4/5 switch associated resitors are not doing their job ??
regards,
Fred.

[Max]

Hi Max,
All OK,
If you disconnect the 330R resistor coming to pin6 of U8 (via 470nF caps), do you still get your offset voltages? if so it may be some coupling , or that the u9 3/4/5 switch associated resitors are not doing their job ??
regards,
Fred.

Hi Fred,
must check for the 330ohm... but notice that the pin6 is dc decoupled by the 470nF cap from that elements, so I cannot see how the e.g. dc level at the 330ohm could propagate effects to that pin giving an increased offset level.

I think the offset is just by internal design on input stage of ic at U8... its own offset voltage at input... that is then amplified by gain of the stage and give the 85-90mV at pin7, causing troublesome behaviour in disc mode.

I will try to disconnect the 330ohm and see if change something or not, anyway, just to eliminate any further dubt.

Kind regards,
Max

[nakky]

Hi Max look at this.Grt Nakky.

[nakky]

Sorry I am wrong.

[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.

[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]

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.

[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...

[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

[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.

[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.

[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.