XL500 sample timing

[porkluvr]

whew

Micheal.
You did some pretty good troubleshooting but I would like to point something out. It is unwise for you to use your expensive machine as a test platform for the VCO. The board could be wired incorrectly, bad components, or faulty design. Find some other way.

Did you try turning the trim pots on the VCO? You never said. BUT.
Please get a powered breadboard and a digital multimeter and THEN do some troubleshooting in a manner which does not put your XL500 in jeopardy. If the VCO board you made has a mistake, putting it inside your machine will not help you locate it.

Your methodology is dangerous (as you may have realized this last couple of days).

[homefire]

Micheal.
You did some pretty good troubleshooting but I would like to point something out. It is unwise for you to use your expensive machine as a test platform for the VCO. The board could be wired incorrectly, bad components, or faulty design. Find some other way.

Did you try turning the trim pots on the VCO? You never said. BUT.
Please get a powered breadboard and a digital multimeter and THEN do some troubleshooting in a manner which does not put your XL500 in jeopardy. If the VCO board you made has a mistake, putting it inside your machine will not help you locate it.

Your methodology is dangerous (as you may have realized this last couple of days).

At least bread board the VCO and us a POT to see if it's working!

[Micheal]

I think I will put the vco on hold for a while.....by the way I did try the trimpots aswell but had no affect what ever I did ...
I am really starting to enjoy electronics,I have been going through the forum and I think I will leave the xl 500 as it is and have a go at making one of the detectors on here ...that way I can learn more ,I like the goldscan IV ,but what I wouldnt mind is something lightweight and powerful in the beach sand at least 40cm penetration for a 20cent ozzy coin.I have done research on making the pcb and it looks fairly simple.The features I really like are VCO and auto threshold I think these are a must...Simple but lots of power is what I want...what do you guys recommend? is there the Goldscan 5 on here because I couldnt find it I would love to make it or something as powerful but more basic in making....please dont discourage me guys I,m going to do this.

[porkluvr]

... please dont discourage me guys I,m going to do this.

Dont Do It!! (I just kidding.)

You're doing good but just don't get ahead of yourself. You really, really need to get some test gear! If you've got the money, get a decent scope, and LCR meter, and multimeter. 3 instruments.

You can find multimeters that seems to do everything (check diodes, transistors, resistors, inductors, capacitors, current, voltage, - I hope I didn't leave anything out... ) but you may have a tough time finding an inexpensive instrument that does all or most of those things WELL.

So, two carefully selected, -specialized- meters would probably do better duty. (That's my uninformed opinion, because I haven't really done much shopping lately. Things may have changed.)

Don't do like I did; for an LCR meter buying a cheap combination LCR/multimeter. My "LCR" meter is practically useless for what I intended it (L and C) and it will need to be replaced when I can afford to do so. For PI work you need to have more "L" resolution than most cheap multimeter/LCR combinations offer. (For IB detectors you want to have better "C" resolution than cheap meters usually offer.)

So, the LCR meter is for just that: LCR. A (DIGITAL) multimeter should handle volts, ohms, milliamps and probably have a diode check. Transistor HFE check is also good to have but don't go out of your way for that feature because a lot of junky meters will have it just to try and look good.

You won't need a dual trace scope right away, but when it's time to power up you should not be without it.

No GS5 is on this site so far as I know. If you plan to build something from scratch you should maybe get some practice manufacturing printed circuit boards. Do some research to figure out which method would suit you (or find someone to do the dirty work).

Some people swear by the "Etch and Peel" iron ons (you need a laser printer and basic PCB chemicals, and an iron). Others swear by one of the more complicated (but more precise - if done correctly) photographic method.

I read not too long ago where someone from Oz said he found a permanent marker available there which works extremely well for etch resist. Not Sharpie, and not Magic Marker... I forget, but maybe you know the name?

Hasn't EVERYBODY made a PCB with a direct etch pads, tape, and a laundry marker?

[homefire]

I've photo copied circuits from magazines to overhead projection sheets and Ironed the toner to clad.

[porkluvr]

I've photo copied circuits from magazines to overhead projection sheets and Ironed the toner to clad.

Laser printers sure come in handy. There are also some brands of photographic printer paper that work pretty good - but take some practice to make narrow traces. Staples Photo Basic Gloss. (Yeah, and I hope I get it right this next time. Those double sided boards are a pain when you mess up.)

(Etch and Peel - where did I get that? How about Press 'n Peel.)

[Micheal]

there is a marker pen available at the local electronics store but I like the iron on idea.its fairly simple you just print out the design using the iron paper on the laser printer ,iron it on and the baord peal it of and dip it in the solution .Its fairly straight forward...But im not sure which project to do.I am thinking the goldscan but I am going to use it on the beach -wet sand So I want something that can go deep on rings and coins,basically small objects (I this is a awsome project and I am really excited ),I will get the scope and LCR meter ( i am also enquiring at my local college for a part time electronics course).... Any recommendations on a proven project guys...I have read tonnes of material on the forum and am still unclear ?

[porkluvr]

Micheal
Goldscan is a complex project. If you haven't done so already you should have a look at Carl Morelands original Hammerhead project. I don't mean just look at it, I mean read the article - and consider building it.

Hammerhead uses many of the same concepts as the goldscan but is a lot less complex and much more suited for a beginner. For beach hunting I don't think you need Goldscan, and definately not for a first project.

Original Hammerhead is not as actively supported as it once was. Carl has started working on other versions using a PIC or something else as esoteric, but there are bunches of people who have built it, and it has its own section in "Projects".

If you build it, PCB patterns (or maybe even ready-made boards) are available but you would need to make choices as you go concerning which variation you prefer. All-in-all, it would be a good learning experience and you'd have a good, cheap, relatively easy first detector to build.

Yes, VCO (as an option) and auto-threshold are included.

http://www.geotech1.com/cgi-bin/page...head/index.dat

[Micheal]

hi there guys I have had a look at the hammerhead ...and it looks fairly straight forward at the moment...I have downloaded and read through the project instructions ,it has given me a lot bit more understanding although I have a long way to go before I fully understand all of it.....at the moment I have drawn it down to 2 options i have one is the hammerhead and the other is the Tesoro golden sabre .......
Whilst reading the stuff on these I have come to the conclusion that the XL 500 needs further relooking at and can be tweaked up much more and is knowhere near its full capability The 5k mod is just a simple mod with just a little more sensitivity and the Monotone mod definitely works aswell,and the coil idea is good also ... But there are more avenues to look at , but now I understand that without the oscilloscope "REAL" experimentation is not possible ....So i think I will re look at the xl 500 with a little more knowledge and start asking questions accordingly.
Cheers guys..

[Micheal]

Hi guys I have made the pcb today using the press n peel iron on transfer film then put it in ferric chloride for 10 minutes and heres the result ,I still need to drill all the holes and cut the excess of the board...what do you guys think of it .Porkluvr have you made the hammerhead pi ...Should I do a new post rather than carry on with it here...what do you guys think?

[homefire]

Dang! Looks Good.

Yes please start a new thread.!

[porkluvr]

Porkluvr have you made the hammerhead pi ...Should I do a new post rather than carry on with it here...what do you guys think?

Very nice! Be careful drilling the holes. You should have a small drill press for that many holes. And of course, multiple drill bits. Without a press, you will get tired and as the drill bit(s) gets dull you will start to miss the mark. And bits break more easily if you are the slightest bit off from verticle.

I have a bunch of SMD parts and so 75% of what goes into my layouts is SMD. It requires a halo-lamp (or good reading glasses) and good solder skills, but it avoids drilling all them dang holes.

I never built a Hammerhead but that is where I first got interested in PI's, from reading that article, that was my introduction to the idea of using a oneshot to develop timing. I knew nothing before that.

I tend to never finish things, because as soon as something better comes along - I'm on it, until something better comes along, and so on and on ad infinitum.
I was interested in building a Hammerhead, but then I read about the Goldscan. SO, I was designing a SMD Goldscan, but then came along the SD2000.

I couldn't make the SD2000 timer simulation work so I designed my own timer for it that makes two different size tx pulses with two different listening intervals.

I designed a timer board and switching regulator board for it but THEN I read something Max wrote so I decided that I should have alternating opposite polarity pulses. So I implemented that change. The single long pulse comes out one FET and multiple short pulses come out the other.

Tinkerer asked me to help with his positive voltage power supply, but then I had an epiphany and realized that I could use a positive supply instead of the negative supply I had. Dual transmitters like in my project begs for a DD coil, and with a DD coil I can use a positive power supply. Better efficiency from the switcher. Serendepity.
Finished last night. You can see it here: http://www.geotech1.com/forums/showt...2390#post92390
Posted five minutes ago.
Now, I either need to finish work on the IB project, or on the PI. Maybe I should flip a coin...

[Micheal]

sorry I forgot to reply to this post porkluvr I am currently working on the hammerhead and hopefully start it up tommorrow...this had been very educational ...as for the sd2000 that thing is too complex.Good luck with it.
In time I think I will go back to the xl 500 to see what else can be done to improve its detection but I need to learn more and its slowly happening.
The problem is that with the big coil it goes deep enough but pinpointing is hard therefore too much digging...the little coil is good for pinpointing but not deep enough and and everyone knows in the surfsand things get buried deep.

[Micheal]

Hi guys ...after more fiddling with the XL500 I have been experimenting with the 5K mod which worked really well making a huge difference in sensitivity,I decided to go down to 4.7K resistor and I have got more sensitivity again ...at this stage it works nicely ,I have tried it on coins and a flat small and thin 5mm stainless steel washer weighing no more than quarter gram and it picked up at 7cm which is awsome for this machine.
I have tried 3K resistor which is too low and the machine loses total sensitivity...i will keep trying resistors between 4.7K down to 4k and try to find the optimum resistor here and will let you know what the results are.


My question is the XL 500 operates quietly at when the Audio knob(which is really the sensitivity knob) is turned up until the there is a tone.As the knob is turned for more sensitivity then at maximum sensitivity which is just before when the tone is just audible everything is sweet .But just after that point turn the knob anymore and then you are increasing this tone louder (similar to a gain or feedback affect)which overides the sensitivity ,so you have a loud tone with no sensitivity at high tone level....why does this happen.I have tried removing the LM358N so there is no tone and what is going to happen and the result was just the buzz from the current is audible to see if the problem is before the final stage and the affect is still there any ideas on squeazing more sensitivity out of this machine.There must be other things to look at besides the 4.7K that can be modded ...help wanted with this

[homefire]

Cool beans on your 500.

I've been unemployed for the past six months scrambling around looking for work.

5k was the best I could do on the mod, I think all machines have a few variables in the manufacturing process.

Any more Sensitivity is going to come from the Front End and Sample Amp I think.

When I have more time , I may play around.

I need to box up the 200 and send it off to the owner here soon.

The 200 is the better of the two machines.

They used shielded cable and I think the coil is shielded as well.

Intended for beach use, they had to address the ground effects better.

I will still have the 500 to play with.


Jim