Surf PI Pro

[multieagle]

Is there a difference between IC L78L05 GE238 (purchased replacement) & 78L05 1122 (original kit)? I would assume anything labeled 78L05 would be the same part. Just want to eliminate that as a concern.

[sled]

Hi,

I had some spare time and put a LtSpice simulation of the SurfPi Pro together to play around and understand the basic circuitry although I'm not sure if the output should look like that

If someone knows and has the time, I'd like to know:

1) Why are the signals to the non-inverting and inverting input of the second op-amp ( LM358 ) delayed? (I have attached a plot of the CD4066 switch trigger signal for the inverting (inv_trig) and non-inverting (ninv_trig) input)
2) Why is there a 100nF capacitor (C4) between the NE5534 amplifier and the LM358 integrator?

PS: One can also export the audio as WAVE file from LtSpice (gives ~600Hz beep in my simulation)

Thanks!

[Tepco]

Your simulation is correct, waveforms should look exactly like on pictures. 5534 must be DC coupled, signal is highly asymmetrical so “baseline” will shift slightly if AC coupling is used. Rest of circuit can be AC coupled however, 100n cap is added to separate DC component, residual offset from 5534 output, to prevent it from interfering with rest of the circuit. First 358 is “differential integrator”, in first sample, signal from target is integrated, in second, delayed sample target signal is already decayed, just earth field is present, and residual integrator offset, these two samples are effectively subtracted to produce output signal. Signal at first 358 is DC voltage varying in presence of metal. Second 358 is connected via RC network, of same time constant as of integrator, this is “motion filter” See original patent for more detailed description.

[sdesic]

Today I found hotbrick
brick from "magnetic" material ...
it is classic red "clay" brick ... old one ... may been in fire
tried to break brick in half and did ... both are hot also ...
"lighter detection"

I tought that surf pi pro doesn't find hot rocks ... not sensitive to them ?

[jfais1717]

I recently completed a surf pi and have been having issues, I am getting +5.8V and -4.5V as well as able to set offset and even adjust threshold. However I have little to no sensitivity. By this I mean that I only get a response at 1-2mm or when I touch the metal to coil.

The threshold tone is solid and I have checked all values on components on board with multimeter.

I do get a humming from the board, but I am lead to believe this is normal...

My coil specs are 10.5" diameter 30AWG @ 19 turns. 440uH and 5ohms resistance.

I have been told that the coil resistance is high but I have also been told that these surf PIs are extremely tolerant machines.

Any help or nudge in the right direction would be helpful(and I dont have access to an o-scope)

[Dixix]

The diameter of the wire is very thin indeed! (0.25 mm).
Pulse induction loves rather thicker wire. From 0.5 mm (AWG24) up.
But in your case, then try to change the dumping resistor. But it is difficult to adjust without scope.
Better get thicker wire and make a new coil.

[Dixix]

I forgot something: Do you know the very informative article about PI coils of bbsailor?

http://www.geotech1.com/pages/metdet...s/FastCoil.pdf

[jfais1717]

actually, I did read this and followed exactly. My inductance didnt turn out the same as his but I attributed this to use a enamel coated wire instead of the teflon he recommends.

This is the reason I think something other than just an incorrect coil is the issue. I had located an article about how to adjust the damping resistor but I can no longer find it and also, someone on there said the damping resistor doesnt need to be changed... So Im not sure what to do there

[Dixix]

Here's a clue. (Dumping resistor)
http://www.geotech1.com/forums/showt...955#post122955

If the resistance of the coil is too high, then all the power is lost. You heat the coil. But you want to transfer energy to the target. That can not afford the small surf PI.

Why not just wrap a new coil? with less resistance. Teflon is not necessary. I have PVC insulation. Enmalled copper wire but goes. Only thicker the wire needs to be.

This is my coil: (i have also tried various coils, but this is the best) 0,5mm wire, thin pvc insulation, in resin cast:

[jfais1717]

the new wire came in yesterday. I wrapped a new coil:

24awg enamel coated single strand with 21 turns, 10.5" diameter. I get 360uH and 1.8ohms

best of all... it works!!!! I can detect a 1 mm thin wedding band at 12"

thanks for the help!!!

[liekwang]

?The real test in the field you are trying to do on the air is there a false signal

[sdesic]

Third in a row Surf Pi Pro doesn't work for me.
Same problem ... don't have -5V on 7660 pin 5

Tested without ICs and no pots ... only IC 7660
7660 is not defective - tryed with new one
I have 12 V on board and +5 V is there too.

Looking for solder oveflow ... but no luck...

PCB design Surfxx
Schematics J. Owen

I have one working surf pi pro at this moment.
Used components from schematics

[Silver Dollar]

Well if you have power on pin 8 and a clock on pin 7 and a cap from 2 to 4 then you should get an output....

[sdesic]

Well if you have power on pin 8 and a clock on pin 7 and a cap from 2 to 4 then you should get an output....

I have +0,72 V on pin 5
On pin 8 there is +5.2 V
Cap is connected ... C13, C14 and C15 are 220uF

[sdesic]

I third pass searching for solder bridges I found it ... now there is -5V ...