XL500 sample timing

[porkluvr]

Hello porkuver and fiends
I have made the VCO as you have described...

Oh, nooo, you didn't. That was supposed to be an April Fool's joke.

(I'm kidding.)

Very nice work, fast too! Is that shiny blue wire teflon insulated?
What you should do is get several different colors of wire so you can color code your connections (in the future). PVC is much easier to work with than teflon, by the way.

You should color code the five wires, using a Sharpie, Magic Marker or whatever brand permanent marker you have in Oz. W2=red W4=black W3=green and you can make the other two whatever you choose. Or don't color code. Five wires shouldn't be too hard to keep straight.

You need to connect W2 to +5V, W4 to -5V, and W3 to ground. Making the connections near the voltage regulators would be ideal.

W1 is the target in. You must find the output from the next to last amplifier in your machine. Hopefully your detector's amplifier chain follows the older versions. Ummh, yes?

Find the base resistor of your output transistor (47k) and connect W5 to the signal input end. Make sure you disconnect from the old audio oscillator (LM35. The connection end will probably need to be left flying. Be careful not to rip the resistor from the board. It this works you can remove the LM358 (and solder the resistor end back on the board) but don't do so yet.

That should be it. I suppose the hard part is finding the "Target Signal" connection point. As I look at the XL500 schematic from Homefire it looks like the junction of the .022 cap and two 470k resistors may be a good place. It's between the CA3140 and the LM741.

It looks like you have a polyester cap for the 4.7nF. If your output frequency drifts you should replace that with PP or PS.

I see that next time I post a schematic I should make a parts list. You could have used el-cheapo 0.1 disk caps for C1 and C5, but mylar (aka polyester, "film") caps are better. Also, C4 should be temperature stable (polypropylene, etc.) because we want the VCO frequency to be stable even as temperature changes.

That's it! Fire it up and watch it smoke! For safety purposes you should wear safety glasses. I had an electrolytic cap explode one time. It became a projectile and missed my eye by about 1 inch. That's no joke.

[Micheal]

Hello porkuver and freinds
I have made the VCO as you have described...I have attached a picture so you can see my first ever electronic poject...The things im not sure are W1,W2,W3,W4,W5,.....I have assumed W=wire so I have placed wires there,If my assumption is correct where do these wires get connected to. And how do I now connect the VCO unit to the xl 500....( Please remember I am very inexperienced so describe accordingly...cheers)

[porkluvr]

I tried to make the reference designators the same (as much as possible) between the two drawings but I left some parts value differences?!! (That's careless.) From looking at a simulation display it's really not possible to know what this is going to sound like so the VCO was in a state of flux up until the time I posted. I could have done a better job of cleanup but I was too excited about finishing.

R4 = 470k (increase this value if VCO threshold frequency seems too high.)
R6 = 1M0
R10 = 10k
R11 = 10k
C2 = 10n ~ 47n or you can leave it out altogether.
1N914 = 1N4148. Common ordinary signal diode.

RV1 should be 100k. If you can't dial in, then try 200k or change one of the ancillary fixed resistors.

R3 can be made lower if you want faster VCO response. Start with 4k7 ~ 10k. You don't want instantaneous transition from low to high frequency or you won't hear subtle differences. Very high VCO gain is undesirable so long as the VCO frequency changes audibly at low signal levels, IMHO.

If you decide to use a pot for R3, use a fixed 2k in series with 10k pot. Me? I would just try a couple different values of fixed resistors and stay with one, instead of fussing with a pot. Don't play with R3 until everything else is dialed in. Changing R3 WILL make you need to adjust the frequency trimpot.

R10, R11 set the range of the level shifter trimpot, so by making them 10k you'll have a better chance of matching with the XL500 target signal level. The adjustment would be less touchy with 22k but it might not provide the necessary adjustment range.

I don't think it is a good idea to have a lot of front panel controls for the VCO but you may want one for threshold frequency RV1. Everything else should be preset then left alone. Even RV1; if you set everything up correctly - may not need be a front panel control. But, there may be something I've overlooked, to makes the VCO go out of adjustment. Using polypropylene or polystyrene for C4 will help here. You may want to bring out RV1 to the front panel, but it should not be absolutely necessary. We hope.

My suggestion is don't drill holes to mount any controls on the front until you are sure that you want them.

If volume is too low, Lower R8 (39k) to increase duty-cycle of VCO. This will affect frequency, however.

I hope I've cleared things up. There should be adequate adjustment range available to accomodate minor parts variations.

Let me know if you have any more questions.

[Micheal]

Hi porkluvr thanks for vco work (very greatful)..I will hopefully start on it this weekend...before I start On the diagrams some of the values are different from one another ...which daigram do I use so I buy the correct parts....
different parts are R4,R6,R10,R11,C2,D1,D3......should i use the diagram from your software or the black and white drawing....
Also you mentiont "Resistor R3 (10k) can be played with to affect the VCO gain. Try 4k7(should this be 47k ) if faster response is desired. I could have made R3 a potentiometer,
but I wanted a small PCB, and a variable VCO gain adjustment is not necessary for sucessfull VCO setup. The other two trimpots are"..my other question is can I use a external mounted pot and what value where R3 is and how would it be wired ..reason for this is for any tweaking if needed and just the extra option.thank you

[porkluvr]

Oh, yeah - good opamps are LF442, TL062, LM1458, etc. No special requirements. LM358 will work but not as well as the others.

Here are the Cadsoft Eagle v416 (Lite) files.

[porkluvr]

Here's a good VCO. This can be built on a piece of perf board or use the PCB layout I devised.

It has its own gain amplifier. Without that, every time you adjusted threshold volume you would also be changing threshold frequency.

Use a socket for the dual opamp because different amplifiers will give you
different frequency ranges. It may pay to experiment, but stay away from doggy opamps like LM358.

In the right box is your existing XL500 circuitry. The left box is what you must add. The circuit is borrowed from Fisher's GoldBug detector.
I borrowed the VCO gain amp from the XL500 audio threshold circuit.

Resistor R3 (10k) can be played with to affect the VCO gain. Try 4k7 if faster response is desired. I could have made R3 a potentiometer,
but I wanted a small PCB, and a variable VCO gain adjustment is not necessary for sucessfull VCO setup. The other two trimpots are.

I worked up a PCB in eagle lite. The layout has not been tested but hopefully I didn't make any serious mistakes.

Good luck. I'll post the Eagle (416 lite) schematic and board files in case anybody needs to modify device packages (or add a pot to R3.)

[homefire]

The schematic I posted is from the forum. It was correct on everything I've looked at.

On the 200 the Pot used for Power on the 500 had been replaced with a single resistor. The 200 does have a different PC board and some track changes.

Most Component are the same, same place and I could follow what was going on with it.

Cool photo you posted!

I'm thinking yours is Newer then the ones I have to work with.

You should see the solder job they did on the 200! Cold joints, Stingers, and a few Globs. Not Good.

It works and works most well. I think the Sheilded cable makes the defferance. I don't know if the coil is sheild or not but it is better then the 500!

The 200 was a surf and beach machine and it has some EMI protections as the 500 has none.

[Micheal]

I took this picture is when I first received it a few weeks ago in original condition without any mods .I will post the newer one with the mods tomorrow

[Micheal]

while I have been waiting for replies I have been investigating the posts about the xl 500 on the forum ..I have discovered that none of the schematics match my xl 500although they are close .I am trying to upload pictures of the main board so that you guys can see.

[Micheal]

I have finally been able to register...Thank guys

[Qiaozhi]

Hi there gentlemen....I have today made 2x 40 cm diameter coils for experimenting using 2 different 12core data cable and here are the results...
coil 1 is 12 core insulated with the alluminium type foil wrapping over the wires ...
coil 2 is 12 core insulated with the alluminium type and the braided wire insulation over that....



coil 1 coil 2
coke can .......................................... 90cm(veryvery faint 95) 86cm
20 australian cent coin........................ 40cm 36cm

First I will tell you this that the cheaper data cable is was the better performer.
Now I havnt tried these coils outdoors ...this test was in my garage shed with a tin roof and I think there is too much interference and I think the coils might go a little bit deeper outside free from any interference when I turn up the power.Any way I am very happy with the results.Although I am too far away from the goldfields. I am really wondering how this machine will work in the Australian goldfields but anyway I will put pictures on here when I get a chance and show it on youtube so we can see the results a bit better for discussion purposes.Looking at IRLMAN video where he finds 28 gram silver at very deep level ..I think this machine will be a superb machine for Larger size gold buried deeply...But that means a lot of digging.I will test the new coils out on the beach in the next couple of days and see how they react in a real test(and maybe find something more than a 20cent coin this time).Once it passes the test I will then somehow make a housing for it.
The other mod I did is the battery ...I put dean connector on it so I now can recharge the batteries with a 1 hour quick charger and it also works very nicely.

VCO and Auto threshold is a must for this machine....Then I think the xl 500 will come to life and in par with the high end machines.

Did you see my previous post telling you how to register and still keep your email address?

Hi there gentlemen....I have today made 2x 40 cm diameter coils for experimenting using 2 different 12core data cable and here are the results...
coil 1 is 12 core insulated with the alluminium type foil wrapping over the wires ...
coil 2 is 12 core insulated with the alluminium type and the braided wire insulation over that....



coil 1 coil 2
coke can .......................................... 90cm(veryvery faint 95) 86cm
20 australian cent coin........................ 40cm 36cm

First I will tell you this that the cheaper data cable is was the better performer.
Now I havnt tried these coils outdoors ...this test was in my garage shed with a tin roof and I think there is too much interference and I think the coils might go a little bit deeper outside free from any interference when I turn up the power.Any way I am very happy with the results.Although I am too far away from the goldfields. I am really wondering how this machine will work in the Australian goldfields but anyway I will put pictures on here when I get a chance and show it on youtube so we can see the results a bit better for discussion purposes.Looking at IRLMAN video where he finds 28 gram silver at very deep level ..I think this machine will be a superb machine for Larger size gold buried deeply...But that means a lot of digging.I will test the new coils out on the beach in the next couple of days and see how they react in a real test(and maybe find something more than a 20cent coin this time).Once it passes the test I will then somehow make a housing for it.
The other mod I did is the battery ...I put dean connector on it so I now can recharge the batteries with a 1 hour quick charger and it also works very nicely.

VCO and Auto threshold is a must for this machine....Then I think the xl 500 will come to life and in par with the high end machines.

[Qiaozhi]

I am trying to register but I am being told that I am banned ( I dont understand why this is happening)...how do you put pictures here coz I would like to put some pictures of the progress so far.

Read this -> http://www.geotech1.com/forums/forumdisplay.php?f=52

Then send an email with the user name you would like to use.

[Esteban]

I am trying to register but I am being told that I am banned ( I dont understand why this is happening)...how do you put pictures here coz I would like to put some pictures of the progress so far.

Maybe doesn't accept you email address, here you can't use, for example, gmail, no problem with yahoo.

I am trying to register but I am being told that I am banned ( I dont understand why this is happening)...how do you put pictures here coz I would like to put some pictures of the progress so far.