XL500 sample timing

[homefire]

Good Ideas on the PW and timing.

I could copy the HH 555 set up with pots.

As for the Photo! All of my photes and Schematics are via Photo Bucket.

If I purge the File all photos or graphics will go away.

If your want them you better save them now.

[porkluvr]

Sorry, I don't have anything on the GroundHog other than what the local search has turned up. Maybe it's similar to Andy Flind's Magnum? Maybe not.

If you change the transmit transistor to IRF740 I have some more possible (and easy) improvements you can make, to change PW and PRF.

And, if you use shorter sample PW you may have better sensitivity to gold. That's a maybe, because those other things might be
considered co-requesite.

On the other hand, you might lose some overall sensitivity (especially to larger objects) by reducing sample PW.
As an experiment you could solder another resistor on top of the 22k sample PW resistor. This would shorten the sample, and would be very simple to undo. Maybe, 47k?? This would give a parallel combination of 15k.

Do a google search on "Reg Sniff" and "Understanding the PI Detector" (two parts).

Hey, how did you insert the dead bug image into the main message??

[homefire]

YeP Changed the Resistor and it's better on Small gold stuff fer sure.

Need to find acess to a Oscope as the one I had access to Did the dead Bug.

This was all on the SeaHunter 200. The 500 Is for the Provider want's the 500 no moded yet and would like to make sure all is square before I Do it and send it off.

As set up it should be hitting the low mark of 17us and Don't have any way to check it out in Salt Water.

As a Ring Fisher he should be ok.

Got a Garrett GroundHog coming Next week!

Do you have any schematics or info on it.

I plan on getting this one working and trying for nuggets with it about 60 miles from here.

[porkluvr]

You Still out there?

Ahh, you're back from holiday. Have you tried any mods to your XL500?

I've been working on a Tesoro Golden Sabre "clone". It's not really a clone because it will have a switching power supply. A 9V battery can be used down to a 3V discharge voltage (cough, cough, at least in the simulator it can). For the audio, I'll beat the oscillator from LTC1044A DC-DC converter against the received target frequency. A two pole active filter can extract the lower sideband (and thank you, BurrBrown FilterPro). There should be -some- frequency information, but it won't be profound. Better than none at all.

This is sort of a VLF with BFO audio. I'll have regulated +/-5V supplies and run the transmitter from 10V, with a 3V~9V source. If you like things simple, you won't like this - although it's not as hard as may sound. It would be impossible without LTspice to work with.

I was working on a LOBO with VCO audio but ran into a problem fleshing out the audio. Buhhh, tricky stuff. My concept was flakey. I need something with better odds of success. I'll learn to walk before I start running.

I'll maybe leave out the TGS notch circuit (much like Ivconic's TGSL) and try to fit my contraption to my Super Sabre II cabinet. The SSII cabinet is pretty small - and the faceplate doesn't have much room for knobs and levers.

How's your XL500 coming along?

[homefire]

You Still out there?

[porkluvr]

Thanks for the info!

Alright, I figured out my problem. The output from the first opamp is a negative signal. For a positive voltage to occur
at the output of the CA3140 (and then the 741) the primary sample goes into the 3140 inverting input. That's what happens.

But I'm not out of the woods. When I wired the rest of the circuit together, the signal to the headphone turned OFF
as the output of the 741 went high. That defies my logic and understanding. As I look at the circuit I am absolutely
baffled at what the simulation results show. Boo-hoo it makes me want to cry. I might have to pull my hair out
before I can understand what's happened. OOOwwww. OOOwwww.
Should I skip it or tough it out. Gaaa. (I should have stayed in school.) When I replace the 2N3906 with 2N3904 It works
to my liking, but I still can't get my head around the "why" this happens.

Moving on. If you examine my output file, observe that the plotpane at the top is drawn on a different time scale from
the other three. Primary sample is delayed by 14us (it should be 12us from the RC values, but I won't sweat over it.)
I extended the secondary delay by 20% by changing from 1nF to 1.2nF. The "target" is something I concocted.

My test circuit can in no way duplicate any overload that may occur in the 709. Sampling at 14us may not be
feasible, so that's why we use oscilloscope. I'll get one some day.

[homefire]

Here is ware I found the schematics.

http://thunting.com/geotech/forums/showthread.php?t=13132&highlight=xl500+schematic

[porkluvr]

I found them both here on the forum.
PCB is there too if you want it.

That's a pretty good knock-off. Instead of just posting the picture, could you post the hyperlink so's I can browse whetever other goodies are available??

So, what's the diffeence between the XL200 and XL500? I looked on Garrett's website for operators manual(s) and all I could find was one, for the "XS-XL Sea Hunters".

http://www.garrett.com/manuals/XS-XL-Sea-Hunters.pdf

I'm working on simulating the scat you posted. It's a pain because, although I have 709 models from three different manufacturers, and even though the models are not exactly the same, they all have the same defect. Only seven pins are illucidated. The 709 uses all eight pins. To salt my wound, two of the pins are simply called "compensation". That would be OK if their connections were mirror images of each other, but according to the device's schematic - they are not mirror images. Which is which, and where is "output compensation"??? Why'd they even bother? How utterly USELESS. It must be a conspiracy to make me go crazy!.

What's even worse is that my CA3140 model run extremely slow. The sim's already pretty slow because of all the 4538s. They're bad slow, but at least they have movement. CA3140's rediculous. I'll need to substitute something in place of it, simple as that.

I need to correct something I did. When I posted the picture showing 616Hz on a transmit waveform it's actually more like 833Hz. F=1/(.1878-.1866). I must have changed an R or C after I took the measurement. How's that for being methodical? Anyway, changing frequency is simple to do with the 555. Changing pulse width is a little trickier because frequency is affected. I don't know the best combination of frequency and pulse width. You'll have to figure that out.

I've still got to figure out the "annuciator" circuit.

[homefire]

The first schematic seems to have been reverse engineered from the board it's self.

The 200 and 500 use the same board. Only exceptions is the power control pot.

The second one is someones knock off I think.

I found them both here on the forum.

PCB is there too if you want it.

Post no. 60 is from...... William Lahr ! I build it, years ago, it is working very good !

[porkluvr]

Before I forget, some PIs have a small value resistor in series between the MOSFET drain and the coil. Something like 2.2Ω maybe more. I just today saw a design using 5.6Ω. I don't think it's absolutely necessary, but it's intended to help the FET run cooler.

In all reality, I do not know why that "small value resistor" is sometimes used. I said "it's intended to help the FET run cooler", but that's just a guess.

My spice simulations indicate that even a small amount of resistance there will severely affect the output signal. I'll leave it at that, for now.

Anybody is more than welcome to add their knowldge to this argument.
Somebody? Anybody??

[porkluvr]

I still don't understand how they are seperating the samples.

Do you know which model is this second schematic you posted?

Just think of the jfets as SPST switches. The one-shots provite the control cignal. Only one switch is on at a any time. The one-shot timing determines their spacing and on-times.

The first part of your circuit is the easy stuff. I'm having trouble understanding what happens after the 741. I'll need to simulate it before I can understand what's happening. Tarrrr-nation. It's damn convoluted.

[homefire]

Yea! Backaswards!



Ok.

14oz

I still don't understand how they are seperating the samples.

You was right! Not 10 h it was 100.

Nap time. Man your OK!

[porkluvr]

Ok! Let's see if I have this right.

Sample one is taken and subtracts noise .
Sample two 15 us later is taken containing noise plus target signal.
Q: Why is the target signal not present in the first sample?
I will try to verify L of coil with this method.

No, that's not what I said. You got it backwards. So, while I'm typing my little fingers off, you are kicked back doing the 12 ounce curls? That ain't right.

Here's what I was trying to say:
Sample1 is (target+noise)......... [ pin-3, + input, aka noninverting input]
Sample2 is (noise)................... [ pin-2, - input, aka inverting input]
Result: (target+noise) - (noise) = target

That's my eighth grade educashun paying off! Time, well, spent.

Before I forget, some PIs have a small value resistor in series between the MOSFET drain and the coil. Something like 2.2Ω maybe more. I just today saw a design using 5.6Ω. I don't think it's absolutely necessary, but it's intended to help the FET run cooler. FETs get NOISY when hot (so do resistors, come to think of it) - which could reduce sensitivity to small targets. Just keep that in mind. Also, a small heatsink on the FET is good - if you can fit it in. IF not, then don't. I would use both a 2.2Ω
resistor AND a small heatsink, but that's just my being a stubborn perfectionist.

Although the average dissipation of the resistor may be less than 1/4W, it needs to handle 7W peaks. So, don't use a pee-wee. 2W should be good. You might be able to lift the drain lead on the IRF740 and solder a resistor to it to avoid having to cut the trace - should you deem it appropriate to use a resistor in the first place.

note: Although the MC14538 has internal connections between the capacitor discharge terminals (1&15) and pin-8, the datasheet suggests that an external path be provided. I suppose it's no big deal - because we are dealing with microsecond pulses. But that's why I show pins 1 and 15 connected to the negative supply and your schematic doesn't.

[homefire]

Here! Just to muddy the waters, I have this one too from the forum: