SURF PI Delay Mods ..... ??

[pelanj]

Thanks for the information. I will build the stock version first and then experiment with your modifications.

[Tepco]

Some more additional notes on this timing mod. Every madness have it's own natural end. As i mentioned before i acquired for free one malfunctioned SH200 without batteries and fixed it, (it is my 3rd SH, collecting them for waterproof casings for my own MD contraptions), and tried to modify it this way. At the end i abandoned this mod (and make another, if someone is interested i will describe). Anyway, i tried "magic" timing on it, 20+20+20+20, that is, 20us pulse, coil recovery (this is 7" shielded coil, can't go faster than about 12uS, originally minimal delay is adjusted to twice that), 20uS sample, 20uS intersample, 20uS second one, frequency somewhat over 8kHz (consumption was ca.260ma).After adjusting integrator offset (and later reducing gain), optimizing Rdump etc. it worked fine... BUT! Keep in mind, SH is static, non-motion machine, no S.A.T. mode. So stability problem became an issue. Aside some warm-up drift, threshold control became somewhat drifty, like walking on knife edge. And 7" shielded coil is not shielded good enough for this, (i don't know how it is shielded, or if it is shielded inside enclosure at all). So capacitive effects and changing surrounding medium (air-ground-water) produced significant variation in threshold level. Very unstable anyway. However, timing trick still worked, i know everyone on this forum will think this is BS, but coin or 2g ring @ 28>cm using 7" coil is reality, many people have trouble achieving this whit DIY Surfs and 10" coils. I didn't want to modify detector in motion (S.A.T) mode, because i intend to use it as a secondary-pinpoint machine, so i eventually abandoned this modification.

And some note on this "extreme "timing modifications in general:

-Problems like this may be expected if machine is not S.A.T. "motion" mode, but with Surf or HHd or similar, will be no problem at all.
-Coil must be shielded like atomic shelter, especially for underwater use.
-This mod is intended for beachcombing purposes only, probably not good for anything else. But when it hits the beach, you will have Rocketdyne F-1 for sure.

[bklein]

huh?

what is a SH200 or SH500?
I do a Google search of these and metal detector and come up empty.

[Tepco]

GARRETT Seahunter XL xxx

[Lev-HUN]

Will these modifications add more sensitivity for small targets such as gold chains?
I've tried a variety of options, but unfortunately without any result.

[Tepco]

Unfortunately not. For gold chains and similar stuff there is only one option: You mandatory must have very fast coil. Something that can provide sampling delay <10us, or8, or6 or as fact it can, and properly adjusted detector (minimum sampling time, Rdump etc) Chain like and some other targets have very fast decay times, and whit slower coils can be only detected at very short range, or not detected at all, you will pick up just rings. And only whit good coil you can consider any modification. If coil is bad, this or any other mod worth nothing, no means to compensate for loss of target information due to slow sampling. This and similar mods can increase overall detector sensitivity (and also add stability problems if coil is not mechanically sound or properly shielded), but cannot fix slow coil issue.

[Qiaozhi]

Unfortunately not. For gold chains and similar stuff there is only one option: You mandatory must have very fast coil. Something that can provide sampling delay <10us, or8, or6 or as fact it can, and properly adjusted detector (minimum sampling time, Rdump etc) Chain like and some other targets have very fast decay times, and whit slower coils can be only detected at very short range, or not detected at all, you will pick up just rings. And only whit good coil you can consider any modification. If coil is bad, this or any other mod worth nothing, no means to compensate for loss of target information due to slow sampling. This and similar mods can increase overall detector sensitivity (and also add stability problems if coil is not mechanically sound or properly shielded), but cannot fix slow coil issue.

Not to mention ground effect problems due to the very short sampling time ... and the Surf PI has no facility for ground balancing.

[Tepco]

Not to mention ground effect problems due to the very short sampling time ... and the Surf PI has no facility for ground balancing.

Ground balancing is not a primary problem for beachcombing machine. Some jewelry can decay almost to the noise floor in about 10uS,or even less, and fast sampling is the only way to pick it up. Simply, take it or leave it (to someone else whit faster machine), this is the only way, ground balanced or not.

[Qiaozhi]

Ground balancing is not a primary problem for beachcombing machine. Some jewelry can decay almost to the noise floor in about 10uS,or even less, and fast sampling is the only way to pick it up. Simply, take it or leave it (to someone else whit faster machine), this is the only way, ground balanced or not.

True ... but you will start to run into problems at the beach with wet sand if you sample at sub-10us. So you're caught between a rock and a hard place. Sample above 10us to avoid the salt problems (but miss small gold) or sample below 10us and be forced to stay in the dry sand.

[Tepco]

Newest version of Surf (pi pro or whatever they call it) can sample down to 8uS as i remember, and no one complains. And even 8uS is questionably fast for this purpose. I never experienced wet sand problem (in normal, nonmineralized sand) whit 4-5uS sampling.

[6666]

Hi Tepco
I just ran across this thread, what type of coil construction did you use to be able to sample at 4-5uS ?
thanks
6666

[Wahyu]

Very Nice topic, thanks