TINKERERS_TEM-TX

[Tinkerer]

Diptrace Oh I wish I could figure out a way to export between the 2!

Cheers Mick

Hi everybody,

attached are the latest DESIGNSPARK files. Enjoy.

I hear a lot about Diptrace. Is it really so good? what does it is better than Designspark?

Is it not just a learning curve?

Tinkerer

[Tinkerer]

I don't think that's quite correct. Adding the capacitance actually slows down the rate of current change, that's whats allowing you to regulate the fly back voltage. However because the TEM method allows you to get more current flowing in the coil before 'switch off' you can sustain a given di/dt for a longer period of time. The net result is stronger stimulation for many targets. However for very small targets that already saturate with a standard PI pulse you probably won't see any increase in response.

Midas

Your analysis is correct. The traditional PI has a higher di/dt per se, but the limit is the Flyback voltage. Also the high current is extremely short in time, so the skin effect is very high.
One fundamental problem with traditional PI, is the coil to shield, cable and Mosfet output capacitance.
All these problems are much mitigated with the TEM method.

Tinkerer

[Mechanic]

Hi everybody,

attached are the latest DESIGNSPARK files. Enjoy.

I hear a lot about Diptrace. Is it really so good? what does it is better than Designspark?

Is it not just a learning curve?

Tinkerer

Hi Tinkerer,
Give it a try, it just seems to flow easy. I tried many tools before I found diptrace. I was in love within an hour! Easy to select the footprint you want, either manual or auto route, if you want to move a trace just click on it, same with a part, just click on it. I started out using the pcb program only, but over time I had to learn to use the pattern editor, then the schematic program and the library editor! Yes in that order too!

The only downside is the pin limit. You can request a free key for 500 pin (2 layer?) The other way around it is there is a free 30 day trial, no restrictions whatsoever. System restore is your friend every 30 days....

Also it can import a lot of different file types, including eagle libraries. See attached pic.

Alright, now time to download your file.

Cheers Mick

[Mechanic]

Hi Tinkerer,

Well after much hair pulling, I have finally got the layout to somewhat resemble what I said in my earlier post! It is a bit rough but you will get the picture. Someone who is a bit more fluent in DS might like to tidy it up a bit..... It would be nice to move the 4 resonant tank caps to the top Lh corner, but it will take me too long! Anyway with the layout as it is it has reduced the size of the current loop a lot. Also none of the high current is passing through any vias.

I must find a way to import from DS into Diptrace........ would have only taken 1/2 hour to do what I have done in several hours..... Who's complaining? Not me!

Cheers Mick

[bklein]

Not really related to the goals here but I noticed your "overvoltage protection" circuit and it looks incomplete plus it will be the first thing to die if overvoltage does occur. There is no current limiting.
OVP would be a good topic in a separate thread...

[Tinkerer]

Not really related to the goals here but I noticed your "overvoltage protection" circuit and it looks incomplete plus it will be the first thing to die if overvoltage does occur. There is no current limiting.
OVP would be a good topic in a separate thread...

Thanks for the tip. Please check the latest files, I added the resistor.

Tinkerer

[hdphilip]

hello Tinkerer,

I've been following your Tem-TX idea, one item I'm trying to figure out is the bucking coil,

what is the relationship between the main coil and the bucking coil, or i should say the physical placement of the bucking coil?

Philip

[Tinkerer]

hello Tinkerer,

I've been following your Tem-TX idea, one item I'm trying to figure out is the bucking coil,

what is the relationship between the main coil and the bucking coil, or i should say the physical placement of the bucking coil?

Philip

The Bucking coil balances the TX coil. Below are 2 very good articles that explain the functions and the building parameters.

In simple words, the Bucking coil being 180 degrees phase shifted, nulls the voltage in the RX coil. I like to wind the RX coil on the Bucking coil. When the coils are well balanced, if I have a Flyback of 500V on the TX coil, on the RX coil I have only a residual of 50mV.

I mention above, that I can sample at any time during the full RX-TX cycle. This is only possible with a balanced coil arrangement.

There is another advantage in the bucking coil arrangement. External noise, like the current generated by the coil sweeping through the Earth's magnetic field, get cancelled the same way. The current in the TX coil is nulled in the RX coil, by the Bucking coil.

It is very easy to balance the coils, however, any minute shift, causes the coils to be off balance. This often happens during the finishing touches of the coil, like casting the epoxy etc. For this purpose I have added an adjustment on the PCB, that allows to correct small balancing differences.

http://www.geotech1.com/pages/metdet...planar_300.pdf

http://www.geotech1.com/pages/metdet/info/coils.pdf

Tinkerer

[Carl-NC]

There is another advantage in the bucking coil arrangement. External noise, like the current generated by the coil sweeping through the Earth's magnetic field, get cancelled the same way.

Careful, most IB arrangements don't help with EMF or EMI noise. Exceptions are Figure-8 and coaxial (stacked, RX-TX-RX) coils.

[Tinkerer]

Careful, most IB arrangements don't help with EMF or EMI noise. Exceptions are Figure-8 and coaxial (stacked, RX-TX-RX) coils.

Yes, this needs a closer look.
TX+, Bu-, RX center tapped.
The Bucking coil cancels the TX signal that is coupled from the TX coil to the RX coil. It will also cancel the signals that the TX coil picks up. But it is a one way road.

The Bucking coil does not cancel the signal that the RX coil picks up.

A figure-8 coil picks up the EMF signal on both lobes, since the 2 lobes are 180 degrees apart, they cancel each other. Hmmm, how do we get the target signal? We get the target signal, when the target is under one lobe only. There is still the TX coil signals.

RX+, TX+, RX-, coaxial, stacked, same diameter. TX+ and RX- cancel each other. There is still the signal from RX+. RX+ picks up the target and the EMI.

RX+, TX- RX- some distance above the other 2 coils. With different coupling things change. Many variations possible. Is there a free lunch somewhere?

Common mode is good for the cables, but does not work for coils?

Tinkerer

[hdphilip]

Tinkerer,

What kind of receive strategy did you have in mind for the TEM-TX ?

Philip

[Tinkerer]

Tinkerer,

What kind of receive strategy did you have in mind for the TEM-TX ?

Philip

The latest circuit I have been working with is here http://www.geotech1.com/forums/showp...&postcount=447

Once I have the new TEM-TX board running, I will go back to the RX and start improvements on it. The TEM-TX and the RX have some run time that shows that the methods works. Now come the improvements.

I would be happy to get your feedback and suggestions for improvements.

Tinkerer

[Halo]

Thanks for making this project.

I used R12= 8.2K on the level shifter. Attached is a picture of output at TP1 (blue trace).
My question is if it is normal to have a ~200mV overshoot with a long decay back to zero?
I've noticed the same thing in other circuits since I got my scope, even on the FET output of my HH2 without coil attached.
I'm trying to find out what causes this... it doesn't seem inductance or capacitance would be large enough but maybe I'm wrong.

[Tinkerer]

Thanks for making this project.

I used R12= 8.2K on the level shifter. Attached is a picture of output at TP1 (blue trace).
My question is if it is normal to have a ~200mV overshoot with a long decay back to zero?
I've noticed the same thing in other circuits since I got my scope, even on the FET output of my HH2 without coil attached.
I'm trying to find out what causes this... it doesn't seem inductance or capacitance would be large enough but maybe I'm wrong.

Is your channel 2 AC coupled? Try DC.

Tinkerer

[Halo]

Chan 2 is definitely set to DC. Probes properly calibrated. Hmm? I wish I had another scope on hand to compare. Maybe someone could post what their TP1 looks like?

A couple other question Tinkerer? Did you have ideas for the 4 FETS and their driver (U3710)? I was going to try 4 IRF740 FETS and a TC4421(inverting). I'll LTSpice this circuit first. For the 24V IN would be battery or boost? I'll post some pics as I progress.

Thanks.