IB Rx coil at Tx off

[green]

Hi Green can I ask a couple of questions, when you were doing your ground balance experiments what were you useing for a pre amp, was it inverting or non inverting , was it one op amp or two and what was the preamp gain, thanks.

Started with https://www.geotech1.com/forums/show...967#post205967 Tried with 1, 2 and 4 DMMT3904's for lower noise(different R and C values). Preamp I'm using now has (2) with a gain of 450.

Missed the 4 in 3904 in schematic. Not sure why it works because of high spike at turnoff.

When I make another I want to try higher emitter resistors, think I over damp some of my Rx coils. Maybe 3k instead of 1k?

[6666]

Hi Green can I ask a couple of questions, when you were doing your ground balance experiments what were you useing for a pre amp, was it inverting or non inverting , was it one op amp or two and what was the preamp gain, thanks.

[6666]

Used double side tape first time I tried a few years back without success. Started winding basket spiral, worked. Awhile back I tried again with double sticky tape, worked that time, made two or three with tape. The last few times I used super glue, works but slow. Tried using double sided with the last small coil but gave up and used super glue instead. Wrap maybe three inches, add a drop of glue, wipe it, continue.

Coils reply #189. Tx is on one side of 3/16inch foam board, Rx on other side. Don't know how close to balanced it is yet.

The coils look very neatly done, in the R/C model world we use both thick and thin Cyanoacrylate glues ( super glue) the thin stuff is like water and wicks into the balsa wood, but there is an extra product called kicker, its probably not much more than a mixture of bicarb of soda and water, but you just spray it on the glue and it sets instantly really speeds up making things, you can also sprinkle dried bicarb soda powder on wet super glue and it sets like concrete.

[green]

Charted 133mm figure8 Rx reply #189 https://www.geotech1.com/forums/atta...6&d=1601513076 vs 133mm mono calculated with HyperPhysics. Close out to 266mm before it starts to loose signal.

IB was close. First coil I made winding Tx and Rx on same foam board. Before Tx and Rx weren't so I could balance coil. Winding both on same board looks better.

[green]

How is your wire stuck down ? is it double side tape ?

Used double side tape first time I tried a few years back without success. Started winding basket spiral, worked. Awhile back I tried again with double sticky tape, worked that time, made two or three with tape. The last few times I used super glue, works but slow. Tried using double sided with the last small coil but gave up and used super glue instead. Wrap maybe three inches, add a drop of glue, wipe it, continue.

Coils reply #189. Tx is on one side of 3/16inch foam board, Rx on other side. Don't know how close to balanced it is yet.

[6666]

Made smaller coil. Inductance close to calculated https://www.geotech1.com/forums/atta...4&d=1600271977 need to add Rx damping resistors before finishing coil.

How is your wire stuck down ? is it double side tape ?

[green]

Thinking about making some more figure8 coils(two round Rx coils connected fig8 with oval Tx). Posted a distance vs amplitude chart awhile back(mono coil). Make Rx coils same as chart. Want to compare distance vs amplitude for the fig8 against the mono chart. I get higher inductance for spiral coils than calculated. More data for comparing inductance. Make smaller coils first, maybe change number of turns pending on test results. Thinking stage, any thoughts appreciated.

Made smaller coil. Inductance close to calculated https://www.geotech1.com/forums/atta...4&d=1600271977 need to add Rx damping resistors before finishing coil.

[6666]

Hi Green, today I rewound my folded fig 8 coil, much neater, folded 328uH equals two 6 inch coils, got to add a 1 meter lead, be interested to see what it does on a detector, hoping it reduces some emi.

[green]

Playing today with the 8inch figure8 Rx. Charted measured signal vs distance against calculated for a 200mm mono to see at what distance the figure8 starts to lose signal from calculated. Looks like around 2x diameter, still not bad at 3x diameter.

[green]

Tried some distance measurements today. Looking at differentiator out after integrator with the scope. Target swinging on a 11 foot maximum pendulum last time. Wanted to test a coke can and quarter this time. Didn't think 11foot maximum would be enough for the coke can. Held target at desired distance and removed quickly today. Wasn't easy to move target and operate scope so I just stored 3 tries with quarter at 24 inches. Loose about 4inches detection distance each time signal is halved. Signal at 28inches should be twice peak noise, should be easy to detect. Noise was maybe 2 times higher today than last time, don't know why. Need to add the rest of the detection circuit so I don't need to use scope.

Forgot delay time on scope picture. Delay time was 20us.

More tests, Quarter_31inches, 12oz aluminum Coke can_66inches

Added comparator and led to circuit. Took circuit outside for less noise. Distance between target and coil was adjusted until led flashed almost every time. Lower yard stick was held just above coil(didn't touch) and removed quickly. A test I could repeat.
GEB off
Tx_500pps
Tx on_324us
Tx peak current_3A
delay_20us
target sample_104us
detection distance_31inches for quarter, 66inches for coke can
GEB on
Tx same as above
delay_20us
target sample_25us(adjusted to cancel ground signal, quart bag of hot dirt from California)
delay_4us
ground sample_116us
detection distance_26inches for quarter

N and I integrator in are connected to amplifier(gain=450) N and I out. Threshold adjusted for 40mV

[green]

Thinking about making some more figure8 coils(two round Rx coils connected fig8 with oval Tx). Posted a distance vs amplitude chart awhile back(mono coil). Make Rx coils same as chart. Want to compare distance vs amplitude for the fig8 against the mono chart. I get higher inductance for spiral coils than calculated. More data for comparing inductance. Make smaller coils first, maybe change number of turns pending on test results. Thinking stage, any thoughts appreciated.

[green]

Tried some distance measurements today. Looking at differentiator out after integrator with the scope. Target swinging on a 11 foot maximum pendulum last time. Wanted to test a coke can and quarter this time. Didn't think 11foot maximum would be enough for the coke can. Held target at desired distance and removed quickly today. Wasn't easy to move target and operate scope so I just stored 3 tries with quarter at 24 inches. Loose about 4inches detection distance each time signal is halved. Signal at 28inches should be twice peak noise, should be easy to detect. Noise was maybe 2 times higher today than last time, don't know why. Need to add the rest of the detection circuit so I don't need to use scope.

Forgot delay time on scope picture. Delay time was 20us.

[ZED]

No worries,just make sure the red wire goes to +VB,i have seen many examples of blown detectors because of reverse polarity connections.

[Ferric Toes]

This should get you going if you have a version one SD2100 (green control box). ...Never mind about the rotary switch,its a mod incorporating the power switch,the picture shows a SD2000 setup but it still applies to the SD2100.
If you have a SD2100 version two (blue control box) it should be the same setup but send me a pic so i can be sure.

Many thanks ZED. Mine is a green box, and this is the back plate with the threshold control and toggle power switch. I will wire as per your picture.

Eric.

[ZED]

This should get you going if you have a version one SD2100 (green control box). ...Never mind about the rotary switch,its a mod incorporating the power switch,the picture shows a SD2000 setup but it still applies to the SD2100.
If you have a SD2100 version two (blue control box) it should be the same setup but send me a pic so i can be sure.