[QUOTE=Chet;198108]
I use Blue Jeans LC-1 Audio Cable at 12.2 pF/ft, it gets close to matching twisted pairs. It is very durable and handles better than twisted wires. And it looks better. If you plan on making a number of coils it is cheaper to buy one long cable and cut to length as you use it. Just toss the two connectors that come already attached.
Hmmm, thx for that Chet, seems like it would be some nice cable to try, I'll have to get some...[/QUOTE] .
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Hi KRinAZ, from post #75; “I measured a 4' length of twisted # 22 Teflon wires with thinner insulation than yours. It measured 39pf on the capacitance meter. Good to know - think there's any coax that would be lower in capacitance?”
I use Blue Jeans LC-1 Audio Cable at 12.2 pF/ft, it gets close to matching twisted pairs. It is very durable and handles better than twisted wires. And it looks better. If you plan on making a number of coils it is cheaper to buy one long cable and cut to length as you use it. Just toss the two connectors that come already attached.
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Hi KRinAZ, from post #77 "I've discussed this coil with Don Bowers and suggested that if a number of us build these coils and would like a housing he could make housings for us. Currently it looks like the housing would be about 8.25" x 10.25" x 1", could be any mount we all agree on (he usually uses the 19mm Whites/Tesoro/Minelab mount tabs unless otherwise specified) We will need to get the cost per housing from him when we are ready, it appears they would be around $15 each (US Dollars) "
Count me in for two housings; I would prefer the Minelab 24mm spacing on the mount tabs. The wider base is stronger and is the standard for most Pulse Induction after market coils except for Whites. Spacers/washers can be used to fit with the 19mm shafts. He may be able to make both widths by having interchangeable tabs on his mold form. The inside height should be a minimum of 1".Leave a comment:
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Thx, I verified again:
R33 is correct - & I measure 986 ohms across pin 2 of U9 & TP10 (measures R33, 1K resistor)
R34 is correct - & I measure 46.4K across pins 2 & 6 of U9 (measures R34, 47K resistor)
-4.96VDC on U9 pin 4 (VCC-)
+4.93VDC on U9 pin 7 (VCC+)
Battery pack power source 11.04VDC loaded - while powering the MPP
So it seems clear U9 arrived DOA, sigh, I will have to order one (or a couple) as I'm rural and there are no electronics components sources nearby (Radio Shack is 25 miles away but that store mostly has cell phones & does not have any of the IC's we use on this project). Will continue when I have the replacement...Leave a comment:
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[ I get a +.017 to -.017 VDC swing (on my scope).]
I calculate .17 volts with U9 removed. If you are getting .017 I would keep looking.Leave a comment:
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I have updated the basket weave coil templates for the increase in the inner wire slot depths from .4" to .55" to balance the wire anchoring in the slots. I have also added a version number to the templates in the lower right corner so you can know if you have the latest. The latest 8"x10" elliptical is v5, the latest 8" round is v2.
8 inch Coil Form v2.pdf
8" Round v2
8x10 Coil Form v5.pdf
8"x10" Ellipse v5
These are intended to be used with 32 turns (6 layers + 2 turns) (or less) of wire with OD up to 1.5mm, yielding about 324uH and around 3 ohms at 32 turns, depending on the wire you use. Smaller OD wire will allow even more turns and higher inductance.
As always, let me know if you discover any issues with these templates, and enjoy!Leave a comment:
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Well I'm having a problem with Step 8 - Second Integrator. Build manual says I should see a +5 to -5 VDC swing at TP9 as I turn the threshold pot. I get a +.017 to -.017 VDC swing (on my scope). The build doc says I should see a voltage change when a target is near but I see no change.
Step 7 went fine and I have a nice voltage increase at TP4 (which feeds into the Second Integrator) with target near coil.
I verified all the resistor values and ohm'd the circuit and no shorts, all resistances what they should be. I verified C15 & C18 are good, no shorts, and they are the right value (with my meter). I do have a +5 to -5 VDC swing at the middle pin of the threshold pot as I turn the pot.
TP 9 looks the same whether U9 (TL071)(which drives TP9) is in or out of the circuit. Made sure + & - VCC at pins 4 & 7 of U9 are good.
I checked everything I can think of, it's as if U9 is dead. It couldn't be, right!?! Of course I don't have another to swap with it - would have to get one online (unless someone knows some gear that usually has them that I can rob).
Anyone know of a way to verify the TL071 is functional (other than swapping it)?
Otherwise, if anyone has something I should check or other ideas I would sure love to hear them! Guess I'm stuck right here...Leave a comment:
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Interesting note on Step 6 - I am able to adjust the main sample delay (the pulse on TP5) down to a minimum of 5.25uS - cool! Now, for a TX circuit & coil that fast!...
I set it back to 20uS for now to be able to follow the build doc. Once MPP is operational I will go right to the mods and this will be set to probably 7.5uSLeave a comment:
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On post #76, "...seems like pretty much everyone has run into problems with the wire slot width..." I meant wire slot depth. The wire slot width of 1/8" seems fine...Leave a comment:
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