IDX-PRO+VDI

[der_fisherman]

The multimeter could be ok, and the regulator may be struglling to keep 8v,,,,, - try a 12v to rule it out.

Nobody else uses 9v cell on 8V reg


as aside, Can you reject ferrite?

where do you live - uk?

Beautifully put and fully correct.....
Andy

[ampirate]

I am using (2) 9v bats to give me a measured in of 16v - should not be a problem.
The 8V Reg warms up a little bit.

I am from nj, usa

[golfnut]

The multimeter could be ok, and the regulator may be struglling to keep 8v,,,,, - try a 12v to rule it out.

Nobody else uses 9v cell on 8V reg


as aside, Can you reject ferrite?

where do you live - uk?

[Koala]

It's hard to say if the problem is with the coil or detector. What is the peak to peak on pin 6 U1

[ampirate]

I tested the VReg and its output is 7.89V probably just Multimeter off slightly.
All Parts seem tight.

Range Tests give me 6in-10in on Coins depending Coin type/size.
Range for large 6in Can is 24in.

With some popup Chatters.

[Gwil]

Just thinking aloud...

Low frequency instability is very often related to inadequate regulation or decoupling of the power supply rail(s). This allows a wobbling voltage to be fed back from one stage to an earlier one, with unfortunate results. Can be caused by an open circuit decoupling capacitor, among other things. Not sure if I'm looking at the right schematic, but the LM2930 low dropout regulator is a lot more fussy about what's connected to it than for example the 78xx series. The datasheet goes into some detail about what sort of capacitors to use, etc.

As I said, just thinking. May not be relevant.

[ampirate]

If only RX Coil and Cap is disconnected then it continuously beeps: buzzz buzzz buzzz ...
If RX Cap and/or Coil is attached then it is random noise,

[der_fisherman]

Right.
What happens if ONLY the receiver coil is unplugged?
regards
Andy

[ampirate]

Thanks for all the advice guys.
I am trying them out.

And it is a Silverdog kit.

[golfnut]

Yes Im with you, that is the filer/amps or differentiators hooting, sounds a bit like russian woodpecker, as the amps have masses of gain over a narrow BW and can become oscillatory as about 70dB of gain there - in band (around 8Hz peak) - I scoped it once and was 125ms = 8Hz

I applied a resistive load to terminate these amps one time and it helped. Also the mid point between the two amps to gnd a few kohms. minor gain reduction but enhanced stabiity.


I modelled the gain and phase of the pair of amps one time in spice and the phase response from in to out, passes thru 180 degrees while there is still positive gain - in anybodies books thats the basis for an oscillator..

try a 22k to gnd from U3 pin8 see if you can tame it

[Koala]

see what your saying and I have an original Classic and that's silent with no coil. With mine I get a rapid tut tut sound that is allways there when I switch it on regardless of settings. However a quick flick of the ground balance pot will shut it up but if I switch it of and back on again the tut tut comes back.

[golfnut]

sure,

but if I unplug my coil - the Tx oscillator stops, so the Rx channels have no gating, plus the preamp has no input and it sounds dead.

In this state, Id of thought all of them should be as good as silent, or at least not oscillating/motorboating/ repetitively chattering.

[Koala]

If you remove the coil wires totally - it should be silent, No Tx, no Rx - does it still oscillate like this?

My build is not quite without the coil. It chirps away. There were a few miner evolutions of the project. So might very from build to build

[golfnut]

With the wire thing and sheilds, yes it makes great engineering sense to split the Tx and Rx wires up. But alas lots of people have made usb2 wire work ok...

The belden cable mentioned in early IGSL posts had 2 pair screened - twice. and was pretty good.

NEL and ML , sunray etc use 2 coaxes, the braids dont touch along the length of the wire.


The amount of coupling you get from the cable is offset by the coupling in the coil and can sum to a few mV.

I read you have 1V pp on preamp output --- this could be lower, if you move one coil relative to the other in the housing.

Your phasing is key to success also - without 2CH scope you need to arrange to reject ferrite... Have you tried this.



You 9V battery is non standard for these builds ---- Get it up to 12V.


Try thin mic coax on the geb pot, --- keep pot leads short, a sprawling mess is most likely to cause problems.


Dont use the small sounder from the kit, as they are not great, use a speaker of earbuds


You may be picking up some other equipment noise, from your house, (long shot)


did you build a kit off silverdog? or is it your own build/pcb


Post some decent images with good resolution/focus so we canread the values etc and we may spot a silly.


If you reomve the coil wires totally - it should be silent, No Tx, no Rx - does it still osillate like this?


Is your TxRx coils over something close to metal.

Did you fit the diode feedback on the geb filter/amp -- is it the right way / did you go for a zener?

you you scope the oscillatio/chirp on the filteramp output before the comparator input. If its 125ms period it is the filter amps oscillating. (As about 70dB of gain there)

keep trying they do pull some things in... like this...



S

[ossamaussama]

Well, I shielded the Coil, besides the Cable.
Board Shield Pin -to- Cable shield -to- Coil Shield.

But its still Chattering like Morse code: beep beeeppp beep beep beeeep ...

chattering check if coil is fine balanced