I have the ebay tacoma 56 square board surf PI DD board, already asssembled.($AU100) It fits perfectly in the Futurekit box- $22 for 4 delivered from Kitstop (Au). My shaft is a telescopic dust broom(handle) Best Buys, $12. A 3x18650 holder supplies 11.1 -12.6 volts. Had to nick a little piece out of 2 corners to fit past the screwhole lugs. This board has 4 external pots.
Bought a s/hand 10x5 ML DD commander for it ($90).
I haven't set it up yet because I have been making a self designed IB/Beat Balance. Designed and etched my own board, but blew the pre-amp. The trimpot on the reg was faulty, and when zero resistance it put 12 volts through the TDA2822 pre-amp and smoked it! Just bypassed it to the LM358n amp. Not as loud, but workable. It was loud enough for a deaf person in a howling gale before. The DD coil was set up on a Matchless detector, I also etched the board for.
Coil shielding is silver powdered milk bag. This needs no earth lead.
It will see a 5c piece at 20cm, on the steel reinforced concrete. 25cm for a 2c piece. At 110khz it is better on gold/copper than silver/alloy. This design, as with the Matchless inherently ignores iron. Small side-cutters signal less than a 10c at the same distance. Steel signalling normal-high-normal. Non-ferrous signals normal-low-high-normal, or normal-high-low-normal, depending on swing direction.
I'm a member on geotech, but I could not believe the amount of corporate dis-information there.
I dis-assembled the ML Commander. It has about 50 winds of Litz wire one side (1.2 ohms) and about 40(?) of (looks about) .3mm enamelled on the other.(13.4 ohms). With my limited knowledge, I am presuming there is a 5:1 frequency ratio which enhances the signal better than 1:1., and eddy current advantages(?).
It has graphited paper shielding, connected to earth.
After the surf, my next projects will be silverdogs Minipulse Rev D (kit), and the XR 71 sniffer(built board) off ebay.
I don't own or know how to use an oscilloscope, but my multi-meter has frequency measurement, and I have just purchased a digital secohmeter(kit).
In my opinion PIs' are highly over-rated. The biggest furphy being their ability to discriminate. It's all well and good to have something that punches deeper, but as soon as the ground conditions deteriorate it must be dumbed down. Indeed much of the Triangle is beyond the settings of any PI. Many production vlfs, including my GMT, also cannot inherently handle ironstone. That is my reason for self-making.
