XL500 sample timing

Its gonna take me more than 2 days for me to decipher the above porkluvr . I will get it in the end,I will wait for your updated version before I do anything.Actually I was thinking there is a red led light that goes brighter as you go over the target and it gets brighter as you get closer to the target and dims as you move away from the target .Once again Im thinking the power source for the led obviosly must be conected to the speaker out( as the volume goes up the red led goes up as volume goes down the red led goes down).Maybe Im being silly but can the + & - connections of that led be used to turn it to sound and a vco made around or from that circuit ...would this be easier , (I know you guys are probably laughing)its just an idea you know I am still at preschool.

[porkluvr]

cheap, dirty VCO

You don't say how or if you measure inductance. ?

Yeah, what he said.

Here's a vco that might work for the XL500, but it is not foolproof. It should be easy to wire but it may not work well "straight out of the box".

Just about all the components are interactive and setup is not as simple as I would like. Some R values may need be changed. There are no potentiometers. The C might need changed for setting frequency threshold.

The output frequency increases for Vc from -5 to 0, but then starts decreasing if Vc is increased above zero. Input voltage must be clamped to ground to limit positive excursions. A level shifting scheme would be nice but that would require a pot.

The major advantage here is that there's no major surgery to see if it'll work or not. Use the existing LM358 but of course some connections will need jumpers and maybe a few extra holes.

Everything outside the box is the existing XL500 and can remain unchanged. Inside the box is what's different.
Feel free to change component values from what I have, in fact you'd better count on having to do some tweaking.

I'll have something better in a few days but I wanted to get this out of the way first.

Hi guys ...thank you for the replys...
I have tried all of these things you are mentioning but I still cannot get any more depth than my previous trials..has anybody made the 2 coils IRLMAN has made ...I would really love to know how they are made but I am wondering the reality of the depth sensitivity figures are correct.If they are true please somebody put them here in detail so we can make them ...thanks guys

[Tinkerer]

Hi guys...My level of knowledge (please dont laugh )in electronics is very basic ,lets say preschool level ...But I catch on real quick I would like to start from the fundamentals and progress from there Basically I would like to start from scratch so I can learn it and understand it properly....
The other thing I would like to ask is at the moment while I am waiting to get a scope and some helpful tutorials I have been tinkering with coils .....So here it goes ....When I touch the + & -leads of my multimeter switched to continuity mode which is also in ohms mode to the coils connector pins (2 wires) I get a reading of 1.2(I am guessing this is 1.2 ohms)I have the small factory coil and the large 12.5 factory coil and both coils read 1.2 so what I have tried now is I have found that when making a new coil I must keep the 1.2 value when trying work out the wire length .So If for example 15metres of #wga 25 wire with the multimetre showing 2.8 I cut the wire short until I get a reading of about 0.9 and then once connected to the coax cable and connector I get a reading of 1.2 Am I doing this right ,am I on some kind of right direction and how much higher than 1.2 can I go without doing some kind of damage to the electronics.Any way I wrap it with plastic coil wrap to test it and it works ok,but with this method I dont get to many winds eg.10 winds on a 25cm diametre ...I have tried diferrent wire aswell and I dont get too many winds .Strength is not as good as the first coil I had made.I have tried diferrent dimensions and I cant go past the figures I Have posted the other day what ever I do with wire length or coil diametre and winds it seems that this is the depth limit of the xl 500.So I am kind of baffled how IRLMAN has got his 2 coils to achieve those results...I really want to make the 14x18 coil and the 3x3 coil,I have tried exactly what he has stated in the PDF but no way I can get those figures for the 2 coil sizes.So has anybody made those 2 coils with success to achieve these results and can you please explain it here in more detail than irlman describes it really is vague so more detail is needed to achieve success.....Thanks guys

Michael,

http://www.eskimo.com/~billb/tesla/wire1.txt

here is a AWG sheet. You can see how many feet for each wire gauge and how many Ohms. If you have a lot of AWG #25 wire already, try using 2 or 3 wires parallel.

Tinkerer

[Tinkerer]

Hi guys...My level of knowledge (please dont laugh )in electronics is very basic ,lets say preschool level ...But I catch on real quick I would like to start from the fundamentals and progress from there Basically I would like to start from scratch so I can learn it and understand it properly....
The other thing I would like to ask is at the moment while I am waiting to get a scope and some helpful tutorials I have been tinkering with coils .....So here it goes ....When I touch the + & -leads of my multimeter switched to continuity mode which is also in ohms mode to the coils connector pins (2 wires) I get a reading of 1.2(I am guessing this is 1.2 ohms)I have the small factory coil and the large 12.5 factory coil and both coils read 1.2 so what I have tried now is I have found that when making a new coil I must keep the 1.2 value when trying work out the wire length .So If for example 15metres of #wga 25 wire with the multimetre showing 2.8 I cut the wire short until I get a reading of about 0.9 and then once connected to the coax cable and connector I get a reading of 1.2 Am I doing this right ,am I on some kind of right direction and how much higher than 1.2 can I go without doing some kind of damage to the electronics.Any way I wrap it with plastic coil wrap to test it and it works ok,but with this method I dont get to many winds eg.10 winds on a 25cm diametre ...I have tried diferrent wire aswell and I dont get too many winds .Strength is not as good as the first coil I had made.I have tried diferrent dimensions and I cant go past the figures I Have posted the other day what ever I do with wire length or coil diametre and winds it seems that this is the depth limit of the xl 500.So I am kind of baffled how IRLMAN has got his 2 coils to achieve those results...I really want to make the 14x18 coil and the 3x3 coil,I have tried exactly what he has stated in the PDF but no way I can get those figures for the 2 coil sizes.So has anybody made those 2 coils with success to achieve these results and can you please explain it here in more detail than irlman describes it really is vague so more detail is needed to achieve success.....Thanks guys

Michael,

here is a AWG sheet. You can see how many feet for each wire gauge and how many Ohms. If you have a lot of AWG #25 wire already, try using 2 or 3 wires parallel.

Tinkerer

coil L?

... I have found that when making a new coil I must keep the 1.2 value when trying work out the wire length...

You don't say how or if you measure inductance. ?

Hi guys...My level of knowledge (please dont laugh )in electronics is very basic ,lets say preschool level ...But I catch on real quick I would like to start from the fundamentals and progress from there Basically I would like to start from scratch so I can learn it and understand it properly....
The other thing I would like to ask is at the moment while I am waiting to get a scope and some helpful tutorials I have been tinkering with coils .....So here it goes ....When I touch the + & -leads of my multimeter switched to continuity mode which is also in ohms mode to the coils connector pins (2 wires) I get a reading of 1.2(I am guessing this is 1.2 ohms)I have the small factory coil and the large 12.5 factory coil and both coils read 1.2 so what I have tried now is I have found that when making a new coil I must keep the 1.2 value when trying work out the wire length .So If for example 15metres of #wga 25 wire with the multimetre showing 2.8 I cut the wire short until I get a reading of about 0.9 and then once connected to the coax cable and connector I get a reading of 1.2 Am I doing this right ,am I on some kind of right direction and how much higher than 1.2 can I go without doing some kind of damage to the electronics.Any way I wrap it with plastic coil wrap to test it and it works ok,but with this method I dont get to many winds eg.10 winds on a 25cm diametre ...I have tried diferrent wire aswell and I dont get too many winds .Strength is not as good as the first coil I had made.I have tried diferrent dimensions and I cant go past the figures I Have posted the other day what ever I do with wire length or coil diametre and winds it seems that this is the depth limit of the xl 500.So I am kind of baffled how IRLMAN has got his 2 coils to achieve those results...I really want to make the 14x18 coil and the 3x3 coil,I have tried exactly what he has stated in the PDF but no way I can get those figures for the 2 coil sizes.So has anybody made those 2 coils with success to achieve these results and can you please explain it here in more detail than irlman describes it really is vague so more detail is needed to achieve success.....Thanks guys

[homefire]

What level do you know on electronics? Where do you want to start?

DC + - , AC Z L, Radio, RF, EM, .........Name a starting Point and I can find you some tutorials.

Back in the 80's I did a 744 hour course in the USAF in Basic Electronics most Communications Based..

I can use all Basic Test equipment , VOM, O-Scope, OTDM, and a pile of other test equipment and I'm Still lost on this stuff.

I have worked one Wide Band HF Radio, Microwave, Fiber Optics, Laser Comms!

This is All New to me Too!

There Was not Internet back then!

I worked on one of the first versions of Internet called DDN, Digital Defence Net Work.

Did you know that the first Packet Switching was done by HF radio HAM people.

They Started this mess! Not Al Gore!!!!

I'm lost when it comes to new computers.

I learned to program in basic and run it through a compiler to machine code to make it faster.

You can't even get a code set for the computer your on any more.



You have the World in your fingers now.

I can find you any Collage Course type materials you need.

What do you want to know?

Hi guys...I thank you porkluvr and homefire for willing to help me with my xl 500 ....I think that the machine has a lot more potential and I love tinkering and modifying things and when it all works its a great feeling...So I will get a scope and a probe and start attempting some of your ideas...the other thing I need to ask is ...I need to accelarate my knowledge ..I need to find good learning resources and maybe some kind of tutorials that might be available on electronics and metal detectors maybe some thing basic then slowly advance my knowlege as I have a real passion for this kind of stuff and so that that I can understand what you guys are saying .I would like to tackle some of the DIY pi projects aswell in the future...Thanks guys

[homefire]

I need a Job!

My unemployment runs out in a few weeks and I Sir, Will be soooooo skewed!


I have found access to a scope but time and money are at a loss right now.

What schematic are you using?

The one I posted here?

It seems to be true on the xl 500 .

the 200 is missing the power setting pot and is the same other wise.

[porkluvr]

My horror story has a happy ending that I almost forgot. The poor detectorist who over-modified his XL500 has a job and some income so he bought a functioning dual trace oscilloscope on ebay. When he got to poking around he realized that he could reduce receiver gain, which reduced receiver settling time, and his machine started working again.

Yesterday's pontificating is over. Today's a new day so I can start all over again!!

I played around with the VCO idea last night and decided yes, it's possible. But I'm unable to flesh out the details without some feedback from you, the victim. (An unfortunate choice of words we hope. My brain is still half asleep.)

Look at this from my perspective. I don't have a physical lab, only a spice simulator. You don't have an oscilloscope. This is not a good start.

edit: IRF640 is not as good imho as IRF740 for IB detector outputs, but you don't need a HV probe to work with the 200V signal that results.

I'm not 100% sure the reverse engineered schematic I'm working from is correct. So, what happens if I do my best to describe a VCO modification, but it doesn't work quite right? But, then you can't tell me what's gone wrong because you don't have a scope to see what's going on.

I have seen similar situations more than once and it is no fun.

I would feel bad on several counts and probably run out of patience before hammering out the solution.

If you are unable or unwilling to scope the detector then I feel that we are not meeting half-way.

edit: IRF640 is not as great as IRF740 for IB detector mod imho but you don't need a HV probe for the scope because you only have 200V instead of 400V.

I am trying really hard to understand porkluvr what you are saying as well as trying to educate myself in metal detector electronics at the same time ....I am still trying to understand the basic terminology....I do have a sore foot so I guess I have shot myself in the foot but dont know about it,but I am keen to give things a go ...I have taken the xl 500 out in the park today and it seems to be running very smoothly.It seems very sensitive ,I still think it has more to offer If only I knew more .... I am really pleased with the results...I have vco on my garrett master hunter so maybe I will examine the pcb and see if I can make anything out of it.I know I have seen someone add vco to their machine somewhere on the net but I just cant find it again...Anyway I think the main and most important mod to the xl 500 is an auto threshold feature that is what it really needs now...VCO and Aouto threshold please help ...

porkluvr I have a solderer and a multimeter which I am still trying to learn how to use...(the solderer I am pretty good at)

I dont think I am ready for a oscilloscope just yet ...

[porkluvr]

there's more

I said the TX is a system. That's only half the truth. The whole detector is a system, is more correct. That's obvious, and so what, you say? I'll try not to ramble.

Lets assume the receiver preamp goes into overload after each transmit pulse and we must wait until overload recovery before the primary sample is taken. (That is pretty much status quo when the preamp is running at gain of (-)1000, as in the XL500.)

If you do something that improves TX energy (such as replace the BJT with an FET) it will very likely result in an increase in the time for the receiver to recover from transmitter "bang". Waiting longer before taking the first sample would now be appropriate.

But you may have also done the 5k resistor mod, which hastens the primary sample. Remember, the receiver remains in overload longer because you have increased TX energy. What is the net result?

You just shot yourself in the foot!!

TX may work great, and RX may work great, but you've forgotten about system wide repurcussions and so they work poorly together.

[porkluvr]

Micheal, so why don't you register?

I'll tell you just like I tell everybody. I don't want this to read like a lecture - but if you want to do any serious modification to your machine you must have an oscilloscope. You're brave to attempt an FET mod without an oscilloscope, but it is unrealistic to expect success. It is not a "drop in and go" modification. I hope I didn't give the impression it was, because it's NOT.

By changing to a FET you would need to change the value of the damping resistor and it is best to use a scope to find a good value. There is no way around that unless you have a set of components that have been previously verified to work together. You don't.

Also, pulse width would need to be be adjusted and you need to be able to see that. And, scope the FET driver to make sure that's OK.

The transmitter is a system and you cannot go and rev it up without looking at it as a whole. With an IRF740 you also need a higher voltage damping resistor. Which reminds me:

If you do get a scope make sure you get a high voltage probe or two. Most probes are not rated for the 400V that IRF740 would subject them to. I have a source for cheap HV probes somewhere and I'll try to dig it up if you need it. (I'll need it, soon - I hope.)
**************************
I think you could remove the .1 capacitor from section A of the 358 to disable that unused oscillator. Definately leave the 100k to ground intact.

If you can make simple PCB you could maybe build a VCO on an outboard and wire it in. But putting it on the existing real estate - I just don't know about that. Then, there's the veroboard option. That could be quick and easy. BUT, no scope, no hope. (Hey, I made a rhyme.) (Sorry)

just a correction I will add is the ring was supposed to be (very very faint at 30cm)