IDX-PRO+VDI

[Dixix]

Hello Mohandes,
There are very good depth of search for a homemade-detector!
If the coil about 30cm?

I also built the IDX.
I'm still waiting on wire (0.7 mm), so then i try to make a coil for my IDX.

Something else: I found years ago on the beach this coin.



I was surprised. Here the beaches are found usually only Euros ....

What country is this coin? Unfortunately I can not read Arabic (only Latin and Ancient Greek and a little bit english ).
Thanks
Dixix

[mohandes]

try a small trimmer - use the 26873 attachment.. Sounds like your making some progress - S

many thanks my guru
when i use this attachment i can imrprove very best , and i adjust it on 200mv.but in middle pot i add 22k and now is 22k+22k = 44k(i change it , true? )
look this pic befor adding attachment



and when i add the attachment in IDX , i use (22n+47n) and can detect at 28 to 30cm
, is it good depth for this coin ?
this is the pic , Yellow is ne5534-6 and Blue is Ref RX coil

[golfnut]

try a small trimmer - use the 26873 attachment.. Sounds like your making some progress - S

[mohandes]

You have a large DC offset at the preamp output of at least +3.5 volts.

That why the Rx signal looks clipped - its saturating on the pos rail..


This needs to straddle the 0V position





Make sure the rails are +4V and -4v WRT the copper around the cct board edge.


I dont know what you have done here to get this.

Put some good 2Mbyte images up in good focus with natural light and we will all try to help you


You could force a better DC offset condition like this...

[ATTACH]26873[/ATTACH]

S

hi dear gulfnut
how can i adjust to 0 point ,U1-pin6 ??
can you explain me a circuit ?or i use your example and add it to my borad, thanks

[Koala]

well done by experimenting with the RX capacitor you have gained nearly 1/3 depth

Best I have had with that size DD is just under 40cm but that is with a 120mv null on pin 6 of U1

[mohandes]

My friend Mr koala
first i change 47n to 22n+8.2n and can mor detect(i set once thershold for all) detect in 28cm
then 22n+8.2n+3.9n detect in 33cm
next 22n+12n+2.2n in 35or36 cm
it is good depth or no?
this coin for all above parts ( 26mm diameter)
but discrimination is not good and i think frist set Geb pot next do it, correct?(when i set Disc in CW fully can not find gold ring fine,not good sound when detecting that and iron things!!)l

[mohandes]

Can someone explain the function of the pot threshod?. Is it necessary in this circuit?


thanks

HI my friend
olease read it :
golfnut

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Guru


Jand

Firsly you have D3 crossed out in the schematic....

You will need this..

Most have a IN4148 in here... as per silk screen - You can use a 2v7 zener also - fit as per the schematic ( i.e. The zener would go one way around, the dide must go the other way around. ) I think we covered this before, twice




The Disc pot when set CW will reject Iron
The Disc pot when set CCW will NOT reject Iron

The Geb pot when set correctly will reject ferrite

I call the Sens pot the Threshold whish is very confusing I apologise.
The pot tha goes to the two comparators - this sets up a small positive DC level for which signals on BOTH Disc and GEB channels must exceed for a tone.

the pot at the top has its main use when in PP - if set too high the tone rings out continuously. So in PP require to back it off CCW so just no tone.
IN Disc mode leave this pot CW almost fully. This puts more positive DC bias on MPSA13 base - so closer to loud conduction. Works a bit like volume in Disc mode, It does reduce volume of HIT if set CCW

regards

[Waka]

Can someone explain the function of the pot threshod?. Is it necessary in this circuit?


thanks

[Koala]

Detector is cased read for work. Very small case and short wires it's a pain to take apart.

Used a strip from a space blanket from a £1 shop. Conductive on one side so thin you can see through it. Did not check if PCB and schematics match just filled the values that was screen printed on the board. Did notice some of the resistors are different to the schematics on the first page of this thread.

[wlewis]

I used Poly(probably overkill)for everything except for the Aluminum Electrolytic ones near the PSU marked with a + on the schematics. C25,C27 and C29 Don't blame me if I missed one out my detector is all bolted up at the moment.

Watch the size if you are using the silverdog board and sockets as two were very tight againt the socket.

I got all the parts today save for a few resistors.. Why did your detector bolt up? I'm not using the silverdog.. I'm going to have to build it out. Separately, What foil did you use to cover the coils? Did you use a conductive spray? Ref: I checked out Dan's coil. Also do you know if the silverdog pcb and schematic match?

[Koala]

Parts question: which resistors are 1% metal? I thought %1 resistors were only necessary in the rx tx signal path? What capacitors should be poly? If I use a lm317t instead of the lm2930-8 do i risk frying components? Thanks

I used Poly(probably overkill)for everything except for the Aluminum Electrolytic ones near the PSU marked with a + on the schematics. C25,C27 and C29 Don't blame me if I missed one out my detector is all bolted up at the moment.

Watch the size if you are using the silverdog board and sockets as two were very tight againt the socket.

[Koala]

Parts question: which resistors are 1% metal? I thought %1 resistors were only necessary in the rx tx signal path? What capacitors should be poly? If I use a lm317t instead of the lm2930-8 do i risk frying components? Thanks

As far as I know in the original Whites IDX only R47 and R48 were a matched pair.

Someone with more design ability than me would be able to say if any others are worth going to 1%

[wlewis]

Parts question: which resistors are 1% metal? I thought %1 resistors were only necessary in the rx tx signal path? What capacitors should be poly? If I use a lm317t instead of the lm2930-8 do i risk frying components? Thanks

[mohandes]

Ferrite can normal be found in broken power supplies, on the end of some cables(the bit that bulges), inductors and old radios (long wave or medium wave)
Set THRESHOLD with PP short so you can just hear the speaker. Then set GEB with ferrite.
SENS pot fully one way will have slightly more depth than the other.
With PP open. DISC turn until iron is rejected.

If everything works as it should but depth is low try experimenting with different RX capacitors.

thanks
frist i should go and by 5cm ferrite,
and next my result here
so thanks
see you later

[Koala]

my friend
my lm358 have error(maybe chinese)i change both of them and know work well(just low depth , i will set it)

thanks again for you Mr and Mr golfnut.
i will try to best adjust that you tell me
i have not ferrit can use magnet ?

EDit:
for adjust i first short pp and fully trshhold on CW and then speaker have a big tone i do not touch more.
then i set Geb pot by frite until cannot detec it
then remove short of pp then by disk can set reject iron.
sens pot for depth,when i CW or CCW not change more and not good discrimination
thanks

Ferrite can normal be found in broken power supplies, on the end of some cables(the bit that bulges), inductors and old radios (long wave or medium wave)
Set THRESHOLD with PP short so you can just hear the speaker. Then set GEB with ferrite.
SENS pot fully one way will have slightly more depth than the other.
With PP open. DISC turn until iron is rejected.

If everything works as it should but depth is low try experimenting with different RX capacitors.