Surf PI Pro

[Jose]

Sdesic
2.3 K seems low, increase to 3 or 4K, if not you take the IRF9640 temperarura, no problems.
If you set the control gain the maximum value, the threshold remains at silecio, even with this control fully open, then redusca R28 to 22K. I had this problem.
Then try to increase the turns in the coil and R2 reduce to a point of compromise between sensitivity and power consumption.
Jose

[sdesic]

R2 is now set to 3.6k and I have 22 cm
gain is now 3/4 and treshold is on max

[Jose]

Threshold to maximum audio tone is heard?.
Silent?

[sdesic]

R2 at 4k I can get 25 cm but it not clear ... making noise with no metal around
must try somewhere without RF inteference
Coil is 40 cm off ground - reinforced concrete
delay pot is at max 9.5k

I will adjust R2 to 3k6 to reduce heating and consumtion for now
it gives 24-25 cm at max gain - with some noise

[sdesic]

Threshold to maximum audio tone is heard?.
Silent?

with max treshold it has some audio - little short beeps

[Jose]

with max treshold it has some audio - little short beeps

I would have to hear a continuous tone.
Test replaced R28, by 22K.

[sdesic]

if treshold is at max and gain at max it should be no sound or constant ?
with delay at max

[sdesic]

what can be done with offset r10 trimmer ?

[Jose]

Sdesic
Pardon the error, is not R28. "Is R18".
The tone threshold should move from silence to audible more or less in the center of the potentiometer, control threshold.
This should occur while the delay controls and max gain.
I leave for a while, then I'm still here.
Jose

[sdesic]

changed that R18 from 47k to 22k
now with tresh at max at sens at half I get silence
and detect 1 euro at 22 cm

[Jose]

Do the opposite.
Try to gain control ("gain") at maximum.
Then reduce the threshold to the point where it gets maximum sensitivity.
R10, set to a voltage between 0 and 500 millivolts, (0 to 0.5 volts), measured between GND and pin No. 6 of 5534. With the coil away from all metal.

[sdesic]

R10 is set - pin 6 has 0,07V

[Jose]

Sdesic
You are between 22 and 25 cm for one euro, and not bad, I think it can be improved, the coil of 21 turns, I get a value of 230 uH, according MiscEL.
Increase the turns in the coil should improve performance. It should also increase the delay, since the original values give 10 to 15 us, for coil fast.
Our homemade rolls, are slower.
To give you an idea, in my SurPI, minimum delay resistance is 25K, (R25) and the delay is 50K pot, with values below works,works just but increases noise.
Jose

[sdesic]

Best results are with gain on 50%
tresh on max (turned to right)
delay on max (turned to right)

[sdesic]

Jose,

Thank you for your help!
I will make another coil with more turns when I receive LRC meter from China.
For now it is good, I must dig a little (not too much deep).
I will try this surf pi pro in field out of power and other disturbance.
Sinisa