XL500 sample timing

[Micheal]

Hi there porkluvr ..thanks for the concern ...Its most definitely is my fault(not enough knowledge) ...you dont have to be sorry thanks for your input I greatly appreciate it...I will give it a go a gain later...
The automatic self adjusting threshold is what I really want for this machine ...something where I can adjust it to the tone level I want and then it just maintains that level of threshold tone automatically without fading away all the time.Do you guys think it is possible to do on the xl 500 and would it be very complicated to do.

[porkluvr]

Micheal - I am truly sorry my VCO would not work for you. Perhaps I made a mistake copying the simulation from LTspice into Eagle. There is no error checking in that process, only my good ol' eyeballs. (Good??)

I spent a good deal of time trying to contribute something that would work - so it's not working comes as a dissapointment, although not entirely unexpected. Your saying "... did not work" gives me nothing to start with to troubleshoot.

Homefire, I think you should consider level shifting and/or threshold adjustment along with the 555 VCO you've looked at. But maybe I'm just over-complicating.

[Micheal]

something like this but very simple

[Micheal]

Using the +& - wires that go to the speaker of the xl 500 these 2 wires go into a independent VCO box and out to a speaker or little separate amplifire which I use anyway
I was thinking of this kind of idea and I dont see why it wont work.Is it possible maybe there is one out there already made like a guitar affects pedal box kind of thing.

http://www.youtube.com/watch?v=faJq4BLI4_8

[Micheal]

That VCO looks a lot more simple do you think it will work ...and how can I convert this to a pcb ....I think it will be possible to take the power from the existing batteries maybe or incorporate it to the xl 500 battery power supply.


What mods have you done that works?
what do you think of the auto threshold idea.

[homefire]

I think the better on the gold was the resistor mod.

I worked on the XL 200 and 500.

Pulling in the sample sees the gold better fer sure.

I was going to take a different route on the VCO.

http://www.ecelab.com/circuit-vco-555.htm

Less parts count and kinda weird.

Problem is More amplitude lowers the tone. Sorta cool.

[Micheal]

here the results in the airtest I did whilst the lm1458 was in the board ,and I really dont know if it is supposed to make any difference to the depth at all but I did an airtest anyway...

20cent ozzy coin...42cm
10cent ozzy coin...27.5cm
5cent ozyy coin...22cm
gold ring same as the one I have used before...27.5cm ..faint but still distinguishable at 31cm
Coke can....84cm

So what I have noticed from this is that there seems to be an increase for the gold ring by about 3.5cm and the aluminium can had a decrease in depth by 4cm-5cm.and the 20cent coin increased by 2cm.
The other thing was that the tone was a bit higher pitch than the lm358..
and the audible pulsing in the tone was faster than the lm358....
seems like is now better suitable for gold(althugh more tests will be required to confirm this)

I would like to ask this.I think the problem with this machine is (and lets just leave the vco thing on hold at the moment)With very slight threshold tone the xl 500 has got decent depth.however the problem is that the threshold keeps fading and I dont know if it is from the fact that as the battery drains so does the threshold,because continuos adjustment is required to push threshold tone up.My question is this and I know you gentleman you have the know how for this.How can we make an auto threshold for this ,is it possible to do ,I think that this is the most important thing it needs.Something where you adjust the pot to the threshold tone level required and lock it at that level so it maintains that level of threshold.I believe that deep inside the xl 500 lies a monster waiting to be discovered.

[Micheal]

Thanks homefire ,that picture is not the is not the same board as mine.Anyway I have tried to wire up the vco and it didnt work,so I am thinking that I didnt get the connection places right...(very rugged circuitry ....still working fine if you know what I mean).
The other thing was whilst I had the lm1458 in the board I tried out some air tests and the results were that it was fine but I wasnt sure if it was doing any damage , so back in went the 1m358. All the connections are as you told me ...but Im not sure with the input and output signal...I will take a picture so you can see ...The wiring is temperory wiring not soldered could that be the cause...

[homefire]

Must be the later version! The 500 and 200 use Bipolar transistors.

(But it does use 2N5566 dual FET.)

I'd like to see how that was set up!

[porkluvr]

Micheal's board has LT1037 opamp, CA3290 dual comparator, and RFP8N18 FET so it doesn't match any schematic seen here so far. (But it does use 2N5566 dual FET.)

[homefire]

Trying to find the other schematic i had on this one. It used 4066 switches.

[homefire]

Is this what you need? The one I'm working with!

[porkluvr]

... This VCO mod is going to take me a few days to work out where those wires go ,so please be patient for any results...

Yes, your model is different from earlier version.

You should maybe get your board and compare to the parts placement pic that Homefire posted (pane #5 in this thread) to get an idea what the differences are.

Of course it would be easier to find your way around if you had the correct parts placement diagram but I am betting that there are more similarities than differences between the older XL500 and your model.

Hang in there!

[Micheal]

thanks for explaining it all porkluver...This VCO mod is going to take me a few days to work out where those wires go ,so please be patient for any results...amongst all of this ,heres something funny for you when I went to buy these parts from the electronics store(coz I cant read schematics yet) I thought the op amps were 2 looking at the schematic so I bought 2 of each ....when I was finished with the little vco board realising there was only 1 needed .I had a opamp and a saddle left over(guess where they are at the moment...Gone lm358 in went lm1458 with the saddle )The XL 500 sounds like its beating faster and stronger now,It works fine however I dont know if it will cause damage but I had to try it ,you know what curiosity can make you do.Regardless of all of this I will do some airtests while this lm1458 is in it ...Cheers

[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 and W4 to +5V and -5V, respectively 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 and connect W5 to the signal input end. Make sure you disconnect from the old audio oscillator. The connection end will probably need to be left flying. Be careful not to rip the resistor from the board. If this works you can remove the LM358 and solder the resistor's flying end back on the board. But, not 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 instead of film caps, but film caps are great. Also, C4 should be polypropylene or polystyrene because we want the VCO frequency to be temperature stable. Polyester caps aren't so great for temperature stability.

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 and it became a projectile. Missed my eye by about 1 inch.