SandPig's a-sqealin'

[Anonymous]

I got some resonators yesterday and tried them out in the SandShark. The SS comes stock with a 3.58MHz resonator, which puts the main sample delay at about 22.8us. I tried a 5MHz, then a 6MHz resonator, and got these results:

<pre>
--------------------------------
Freq. (MHz) 3.58 5.00 6.00
Pulse delay us 22.8 ?? 14.5
--------------------------------
1-cent 8.0 8.0 7.5
Nickel 9.0 10.0 10.0
Dime 7.5 7.5 7.0
Quarter 8.0 7.5 7.5
Half D. 8.5 8.5 8.0
Silver D. 9.5 9.5 9.0
Mens 14k band 11.0 11.0 11.0
Ladies 14k ring 7.0 8.5 9.0
--------------------------------
</pre>
.

All coins US; dime, quarter, half & dollar all 90% silver; all measurement inches, air tested; SandShark was set to max. pulse width and non-VCO mode, used a 10.5-inch coil.

The big improvement was in the ladies 14k ring, which was relatively thin. The men's ring was a 8mm wedding band, no change on that. Slight degradation with the coins, except for the nickel.

I expected the audio frequency to increase, which it did, but it was still very decent. The VCO mode is higher but still pleasant, and the non-VCO frequency is adjustable so it can be set to a low frequency even with the 6MHz resonator. The PIC chip is having no problems, either.

This looks like a winner to me, so I'm gonna stick with 6MHz. I'll haul it Florida in July, see how it does in the surf.

- Carl

 

[Anonymous]

Good report Carl, for the non-laymen, is changing the resonators difficult? I think some where looking at the possiblity of nugget hunting, would be interesting if you have gold or lead at say 10 grains and 5 grains to see how the 5 or 6 will detector. The 6 should respond about like any of ther PI's with 15uSec, the 5 should do a good job at 5 grains maybe lower, Thanks

 

[Anonymous]

By lowering it to 15uS. it becomes a little more sensitive to lower conductive items like the nickel, and the ladies ring.
The assumption that it being at 15uS. and it will respond just like any other 15uS. unit is not quite right. Although the pulse delay is the same, circuits are different on how they handle the returned signal. Looking at the test on the nickel, (the standard that doesn

 

[Anonymous]

The resonator is a white ceramic surface-mount device, made by Panasonic and labeled "3.58" on the top. It is a royal pain to get off the board, because it's SMD and is soldered to some large pads. In fact, I had to take it to work where we have some specialty irons for SMD that heat all the leads at once. You are not likely to get it off with a regular iron, unless you break it in pieces, which risks damaging the PCB pads.
I don't have any gold nuggets, but I can try lead.
- Carl

 

[Anonymous]

Bill's absolutely right. Just getting the delay the same as other machines doesn't make it as sensitive. There is also coil resistance, damping, and how the sampled signal is processed.
The measurements I made were for good repeatable signals, something I would consider easy to distinguish and make me want to dig. I agree that the SandShark is a mediocre detector, especially with the stock 8" coil. I also suspect part of it is due to the printed spiral coils, and have been wanting to wind up a custom coil.
I'll take these same targets, and try them on a SMPI.
- Carl

 

[Anonymous]

Carl,
I haven