Andy Flind MFD.

[abdou2014]

is those winding are necessary, and what is their detail ?

what are the changes to detect a watch, I do not think that will detect anything without

reaching this sensitivity ?

[Geo]

If the gain is ok then you must receive the watch (at least if you touch the watch to the coil).
Do you have oscilloscope and signal generator to test the MFD???

The small coils at Cryfton don't do anything. Constructor use them with gold sample and try to catch the phenomenon. He says that this small coils with gold paper is gold filter. Anyway, averyone can say it as he like.....
For me 30 turns are enough, just tune them at 80Khz.

[Geo]

Here a photo from my Andy Flind's MFD as lrl

[abdou2014]

is there a difference between the coil location :
the coil below the PCB and in front of 12 cm ?
the coil is it shielded ?

[Geo]

No it is not shielded.
The distance is a small secret: lol :: cool :.
So ..... if the coil is near to pcb and to buzzer, then when the buzzer beeps there is feedback to the coil, and all leds turn on and beeps continuely.
If coil is far then .... NO problem.
This Trick is a present for you ...

[abdou2014]

Thank you Geo , to be precise, this inconvenience is caused only by the buzzer, or even the PCB ?

[Geo]

As i remember, from buzzer and coil

[abdou2014]

so I remove the buzzer to keep my design , I think it's the speed that made Andy flind MFD particular ?

[Geo]

It is a good way... but if you will see problems remember to move the coil.

[abdou2014]

there is a remark that I would like to have some explanation :
there is OBMD builder that used all regulator 100mA, the small,
and others who have used the 100mA just in the ANDY LM 358, and the others all a big regulator 1A, is there a diference and what is the right choice ???

[Geo]

No Problem, all are the same because the total consumation is lower than 100ma

[abdou2014]

Thank you Geo !

[Geo]

What preamplifier do you use???

[abdou2014]

Your Email ?

[abdou2014]

I have never used the audio stage, only the VU meter and I detect a magnet at 1 meter and TOTEM transmitter at 5 meters, I do not know if the 4066 + 555 will give more amplification or sensitivity ???