lobo improved

[tchoci]

To put NE555 timer or SE555 but in any event LM555-I know from experience.


Tchoci!

[tchoci]

Hello to vsichki.sazhalyavam, chenyamah time to participate in outings with diskusiyata.Byah of Lobo and was very pleased with it nego.Ostavih frequency = 17,2 KHz, because I want to catch different types of fine bronze coins in Bulgaria they have a lot also catch large coins dalbochina.Ima good to gold, so I think some frequency = 17-18KHz priemliva.Po is a higher incidence in low sensitivity to the subjects in nadalboko.Osnoven problem generator transistors is "tried a lot, but at my sound into a 2T914A.
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[FOMA]

Hy ALL.
Has Selected the resistor R10.

[maxbiri]

I porkluvr

I stopped the lobo project because poor deep end no time for hobby;
i can resume project in the next days, let me know where i must connect probe referred at my last schematic and i will take pictures from oscope.
In my opinion tx capacitor must be selected for resonance around 20 khz, the problem is rx capacitor, it affect the phase of signal and these is more important respect amplitude.
If i remember right best conditions, on my pcb, is with a 1.3-1.5 nf rx capacitor.
I suspect that all my problems of low deep are a conseguenze of non perfect rx phase.
Circuit is very stable even at full power with no false signal even if i have pcb on desk without schield.
Sorry for my bad english.

By Max

[porkluvr]

Max, Foma,
Thanks Max It's hard to keep up with this project because everybody seems to have different ideas about what works. That's OK, but without proper explanation it becomes a hodge-podge of confusion, especially when there are as many unknown quantities as this started with.

Max, A while back you offered to post some scope shots. If that offer still holds, we'd all appreciate it - or, what about a schematic, updated with your parts choices?

My detector will get finished before summertime, or I'm not the Duke of Windsor (approximately).

[maxbiri]

Hi All

On my pcb with 2.5% tollerance capacitor around 555 i have 20 khz with pot set near half. May be problem is a capacitor with large tollerance +-20%.

By Max

[porkluvr]

I read Tesoro com. No need this believes.
Frequency Tesoro Gold(en) Sabre there 12 Khz
But indeed 15kHz.

What does that have to do with LOBO?

It's nonsense.

I provided a link to the LOBO manual which plainly states 20kHz, not 12kHz, not 15kHz.

Operating FrequencyApprox. 20 kHz
If either 15kHz or 17500 is approximately 20kHz, then I am approximately the Duke of Windsor.

[simonbaker]

We need someone with actual Lobo to put oscilloscope probe near search coil and measure actual frequency. But make sure very clear which model (version) it is!

Cheers,

-SB

[FOMA]

I read Tesoro com. No need this believes.
Frequency Tesoro Gold(en) Sabre there 12 Khz
But indeed 15kHz.

[porkluvr]

VR2=0, R4=14k7 C1=2H2 under such parameter F=17500HZ
Ñ1 I did not change.
But who has measured the persisting frequency LOBO?

Why would you chose the operating frequency at 0% pot travel?
What is meant by Ñ1? I do not see it on the drawing.

I am not an authority, but here is my logic: When an engineer designs a circuit that requires potentiometers for frequency setup, he will select component values with the goal of making the target frequency easy to attain. Preferably, that target frequency will occur with the potentiometer somewhere near its center of adjustment range. It would be a poorly engineered product if it was needed to turn the potentiometer all the way to one end or the other to attain the correct frequency.

Here is a link to the LOBO manual: http://www.tesoro.com/info/manuals/older/lobo/
20khz is listed as the approximate operating frequency.

When I setup a LOBO simulation with the component values shown in our "faked" schematics, I obtain 20kHz operating frequency with my virtual potentiometer turned to about 45~55%, depending on which way it is facing. (Ah-HAH! That was good Tesoro engineering!)

You show that 17500 is your operating frequency, which would be OK except that it can only be obtained with the frequency selection potentiometer turned all the way to 0%.
And, (assuming that 47H is .047 microfarads, correct?) according to the tank circuit components on your schematic, 20kHz would your approximate operating frequency. That's from basic electronics math. You say 17500, but the component values say 20000. I think those two numbers are not very close.

Soooo, you are either driving the coil circuit off resonance or else, more likely, your tank circuit components are not as shown on the schematic. You give confusing information.

Because correct phase reference and demodulation setup depends on having correct operating frequency, I cannot know what to do from following your drawing because 17500 and 20000 do not match.

[FOMA]

VR2=0, R4=14k7 C1=2H2 under such parameter F=17500HZ
Ñ1 I did not change.
But who has measured the persisting frequency LOBO?

[porkluvr]

correction

I think Math's fun. I'm not real good with it, but it's fun.

[porkluvr]

Thanks, Foma. Most of the schematics posted so far have had some IMPORTANT information missing, or else did not agree. Maybe it's because of lack on commonality in the coils - different coils requiring different capacitors.
The first schematic I saw was totally lacking probe information. There have been several diffent versions seen here so it's hard to know which one is best.

Your schematic is very complete, you have information for both the TX and the RX coil sections. But I just noticed that you are showing 17500 for the TX frequency. I am confused because Lobo is supposed to operate at 20k. SuperTraq works at 17.8. There is no mineralization control, so this cannot be a supertraq.

Another problem I see is that if the TX coil and capacitor are 1.33mH and 47nF (.047uF) then the natural resonant frequency for the tank circuit is about 20000. So instead of giving good information this is just adding confusion.

Another thing: I might be wrong but I do not believe that the component values shown will allow the 555 to output 17500 (except at the very end of the frequency trimpot's travel). So, what is going on here? I don't think you are intentionally giving bad information, but this is not what I am looking for.

[FOMA]

C5-very important capacitor, it is necessary to select with each sensor.

[porkluvr]

Tchoci, do you have measurement for your RX coil inductance? I think I can go back through earlier posts, get coil dimensions and then use that data to calculate inductance, but that method is very inaccurate.

Even a relatively small amount of change in coil value would affect receiver phase, so any more information will be greatly appreciated.

Forgive me if you have already stated this. I saw transmit inductance but I can't find it for your rx coil.

Thank you.

Almost forgot- I am looking over the schematic where you marked 2x2.2nF (4.4 total) for the rx capacitor but I read an earlier post where you said 1.3nF. Which one is correct?