FAT THAT 1 - My Latest Project

[FatBob]

I've been wanting to do a PI with differential input for some time now so I
took several circuits and glued them all together.

There's Moodz protected FET isolated front end and Tinkers 3 channel signal
processing back end. Then I added my own tiny clock chip.

I'm close to building it I realized I need high voltage resistors in the front
end so had to order some. I'm sure there's some mistakes and problem areas
but it should be fun to mess with!

Here's the schematic;



And a perf board layout (all the connections are not pictured).



If anyone sees some problems or has idea's for improvement I'm all ears!

[Davor]

I'm a bit puzzled with a 10n capacitor that follows 1k resistor after THAT.
Otherwise it is a clever setup.

[Tinkerer]

Tinkerers RX board

Would you like my old board to play with? I would donate it if you want to further develop and improve the design.

[FatBob]

Davor your right that cap slipped in.

Tinker sure I'd love to have that board to work with.

Here's the mono diff version;

Schematic


Layout

[Tinkerer]

Where do you live?
Send me your address by PM.

[Tinkerer]

I'm a bit puzzled with a 10n capacitor that follows 1k resistor after THAT.
Otherwise it is a clever setup.

You are right, this LP filter is very low and will delay the first sample very much. Obviously a mistake in the value. A better value would be 1n or 470p.
The 1k resistor value is meant to limit the output current of the THAT.
One thing about the THAT, It has a very good noise figure at high gain, but at low gain not so good.
It would be good to check all values on the schematic in detail, as there are probably many more mistakes.

[FatBob]

I plan on running the THAT at 1000x. I realize this is not a finished design and hope
to "Tinker" with it a bit to polish it up. Truth be told I tinker more than actually using
my metal detectors in the real world.

Here in Florida it is too hot right now to be outside for any length of time so it is a
good time to tinker a bit!

[liudengyuan]

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[liudengyuan]

Where is the coil? Several coil? How the clock chip is designed, and the frequency, pulse width, time delay, you what is the purpose of increasing depth? Increase the stability?

[FatBob]

Here's a version with the XR2206 for a VCO with amplitude modulation;


The XR has a second resistor for a different tone. Maybe we can use that for an FE tone?

I have a test coil wound up using some Teflon coated twisted pair and a separate thread
with some code for the PIC chip. I need to build some hardware and try a few different things
before this becomes a buildable project. For now it's just a glimpse into my thoughts and ideas
for a different detector.

I have wanted to try a differential coil for a while as I believe it will work better. This is my
try at making something a bit different.

[FatBob]

I made a couple of homemade Vactrols today. A couple of LED's and some CDS cells
and an old pen is all it takes!