SURF PI HELP

[porkluvr]

The original Surfmaster used a trimpot on the PCB to set the minimum sample delay time.
If your primary sample is colliding with the trailing edge of flyback, you may need to increase the value of the fixed resistor in the primary sample timing circuit.

To try and stabilize the coil field before switch-off, you could try this mod:

1. add 5.1Ω series resistor.

2. Replace R2 with 8.2kΩ

3. Replace R1 with some parallel combination that totals ~89.3kΩ.

note: The original tx timing circuit used precision resistors. Changing R2 to 8k2 increases PW, but lowers PPS. Reducing R1 to ~89k3 will re-adjust the transmit PPS to approximate its original value.

The 5.1Ω resistor dissipates less than 1/2 watt but I would use a 1W resistor if it turns into anything permanent.

This mod would allow the coil to charge to about 95% of its maximum value. There are other combinations of series R and PW that would work.

But, seriously I don't know if this would be worthwhile and it would increase battery drain by about 50%.

good experiment?

[daverave]

im grateful for all your help to me on this...i need to try this cause i know that the detector can proform better than its doing...the diagram you enclosed..is that the original whites pi spec ???? if so why was the original altered ??? for now rather than mess around with my original pcb im going to partly make a second pcb and experiment with that and if i get improvement then i will alter my original pcb.

[porkluvr]

This has been doctored, but I think it is a pretty fair representation of the original drawing.

[kt315]

...

Change out #Q2= TIP32C with a IRF9640
Replace the 220 ohm resistor with a 390 ohm resistor (1/4 watt)

When finished installing the components cut a piece of aluminum foil 3/4" square.
We will use this to adjust trimmer pot #R25 turning on the unit and adjusting
the threshold so you can just hear it, adjust R25 for best response when the
3/4" foil is passed by the coil. This should do it.

You can try removing diode #D3=1N4148 and installing a jumper in it's place.
This will allow a little finer adjustment of the threshold on the soft deep ones.

[daverave]

thanks mate for that original spec...did the original surf pi work better than the modified version ???

[daverave]

i did some tests today on my surf pi and its drawing from the batteries only 37 ma with no signal present...seems a bit low to me...i think thats why im not getting the depth on some items...i can hear an english old penny at around 12"...what you think anyone ??

[WM6]

12" on penny is great result, low battery drain too.
Even more, such good result you can expect in soil too (not the same thing with VLF air tests).
Congratulations.

[Qiaozhi]

i did some tests today on my surf pi and its drawing from the batteries only 37 ma with no signal present...seems a bit low to me...i think thats why im not getting the depth on some items...i can hear an english old penny at around 12"...what you think anyone ??

I would say that's a good result.
What depth were you expecting?

[daverave]

i was expecting around 14 - 16" on old uk penny...i get about 6" on a thin section gold ring (small) cause my coil is 5 ohm and the current is 37ma i feel maybe i should increase tx pulse to around 100ma...surely a pi detector should draw more than 37ma....what you think ????

[Tepco]

Use larger diameter wire for coil, resistance of 5R is too high, limiting peak pulse current, keep it below 2R, do not add any resistance in series. Normal consumption is around 50-60mA.

[daverave]

i will have to use the 5 ohm coil as its already made but will make sure from what you have told me that the next coil i make will be low resistance...cheers for your help with my problem.
thanks Tepco.

[daverave]

i had a friend visit me today and he bought with him his whites dual field pi...i was hoping to measure the inductance but pcb had plastic box around it which i could not open so i gave up....but i did take current measurement and was supprised to see that it only draws about 44 ma from the batteries....i compared the depth with my home made surf pi and there was very little difference...both detected old uk penny at 12" but on a thin section 9ct gold ring the dual field did about 8" which was about 1" more than my machine...but on a small thick 18ct gold ring only about 8-9" which i felt was dissapointing from the dual field...but noticed even small silver ring gave good depth compared to gold item of the same size.

[kt315]

the inductance of the coil will be not something fantastic... it is ordinary classic for PI in 300-350uH range.

while main issue for us is to get an inductance of inner winding and an inductance of outer winding, being splitted one from another. second issue is damping resistor's value on inner winding. then we get all data we can right count the coil.

[daverave]

my detector has a problem which i have to sort out...i was doing some wiring last night and now the audio is pulsing instead of steady...when i turn the delay control seems to get worst...hope i can fix it.

[geoscash1]

daverave, were you able to sort out the pulsing in the audio? mine has that same issue, no steady threshold, just very erattic and very hard to distinguish signals beyond 6 inches at all with all the noise..