DELTA PULSE / SNIFFER XR71 PULSE INDUCTION METAL DETECTOR

I am building my own Tesoro right now, and made a coil plan, if you want I can share it.

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Hello Forum,
If you do a google search on ""aware of chinese electronic components" you are going to be amazed!Thats why such high discrepancy of results from person to person on DP and others.
here is an article:

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I agree it is about the knowledge but it is about components too! One can have a completly well built by schematic circuit and have a totally different result then others. I believe Tuxnor and others was talking about good quality componets.. and  topic must be more debated on...we will get better result when we get to use the right "quality": components...But quality componets from where China?

Regards
Marius

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		Quote:			Posted by BR*simonn
	Hello my friend. Firstly sorry about my bad english, ok?

Hello. Don't worry about English. So far I can understand you.  

		Quote:			Posted by {author}
	I am building my DP, but I have some problems. Can you help me?

I will try as much as possible.

		Quote:			Posted by {author}
	My DP are using 2 eletrolitic of 4.700 in parallel. This is correct?

Yes, that is correct.

		Quote:			Posted by {author}
	Bobin: 32 turns of 0,5 mm wire / 25 cm diameter. when the bobin is disconnect, all the potenciometers apparently works (the noise increase and decrease), but with the bobin connected, apparently the 3 first potentiometers (20 , 50 and 500k) don't work .

Uh, that may indicate many things. Can you provide us oscilloscope trace of the timing diagram, and outputs after first operational amplifier (Tr1, Tr2, Tr3, Tr4, and Tr5)? Without that it is hard to tell what is wrong.

		Quote:			Posted by {author}
	I check all the components and PCB many times.

Well, maybe you should check it again lately.

		Quote:			Posted by {author}
	My DP works, but the detetion is poor: 1 gold ring  = 18 cm / 1 aluminium coke = 40 cm.

Yes, that is about what I get without proper adjusting of the pulse width, timings and other things. Still, after adjusting - detection range is not much better for small targets, only for large targets. Which transistor you use for T5? On circuit, there is BC546, but that transistor play some important role for sensitivity. I used BC546C (high gain). There is difference between BC546 A, B, and C in it's amplification. A, has low amplification (x220), B modest (x330), and C high (x600).

Also, adjust first delay properly. Second delay has "sweet spot", somewhere about midrange (at center) where sensitivity is the best, and depend of coil type, and dumping resistor R5 (parallel to coil). In case of 400 uH coil, this spot is at center of the second delay pot, but with higher inductance it is moved to the right (pot clockwise).

		Quote:			Posted by {author}
	In other post, You instruct to change the diode 1N4001 for other. This is help?

Diodes VD8 and VD9 are 1N4148 in original circuit. Replace that two diodes with 1N4001 or 1N4007 (I replaced it with UF4007, only because have plenty of this diodes). Using 1N4148 may cause it's failure after whole timing/analog circuit drain too much current (various reasons - circuit shorted, burned other parts...).

With voltmeter check voltage between -12V and -E (Tr9). You should read about 1.4V. If close to 0V or much higher than 1.4V, then this diodes are damaged. That may cause bad performance you mentioned. Also, between -E (Tr9) and +E (Tr0) you should read between 10.5V and 11.1V (depend of how well is lead acid battery charged).

		Quote:			Posted by {author}
	Thank you very much.

You welcome. I hope my answer helps.

Regards,
m--

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P.S. Here is how my DP MD works:

<a href="

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		Quote:			Posted by BR*simonn
	Hello PowerLab. Thank you very much for your patience of a Saint. I am just a confused hobbist. Best regards, my friend. Claudio (BR*SIMONN)

You welcome. All we are confused sometimes, especially with schematic that not worked properly, or if we do some mistake. Don't worry, just ask, and someone will answer.

Regards,
m--

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		Quote:			Posted by BR*simonn
	Hello again, PoweLlab. I am still have problems with my DP Delta Pulse.

Heh, me to. Last night realized that one 4066 bilateral switch not working properly. Reason is damaged IC. Seems that I damaged it in earlier stage of building DP. I replaced it with 4016, but result is not much better because already did many changes in auto-tuning circuit and integrator part.

Unhappy solution is to make sense (or gain) pot after main amplifier. When amplification changes, auto-tune changes too - and lead to instability. When signal is strong, this ruin stability too. I compared how it is made in GS4 and Hammerhead, and make some hybrid.

In GoldScan 4, pot gain or sense is last in whole chain of amplification - in DP it is first after main amplifier.

Auto-tune is now separated and signal for tone generator is feed from integrator, not from auto-tuning circuit. But it drastically reduce sensitivity. Now, I have to add proper integrator, but also another amplifier for the signal. By changing circuit and using part of auto-tuning from GS4 circuit, got possibility for "hold" function, and different reset of operating point (also adding one trimer for manual offset point).

Hold function disable auto-tuning at point where it already made proper offset for amplifier (by feedback control of auto-tuning circuit). I abandoned DP project and made big changes, so I can't back and will not back to this project any more. I will make prototyping board and make my own hybrid.  It will take some time, but hope will get exactly what I want.

Core part of DP is made more or less correctly - driving and timing circuit, auto offset for first amplifier, but the rest I not like. First at all, I can't change first amplifier to anything which has not jfet or mosfet at input. NE5534, LM318, AD843/5/7 or other non-jfet input opamps excluded. LF357 give the best result, but I haven't one. I have LF357J, Motorola product (ceramic package) - which is bad because it has some temperature compensation, which ruins slew rate.

Oh, not to forget - second and third amplifiers (D5A and D5B) works better if using TL072 instead TL062 - slew rate increased from 3.5V/uS to 13V/uS. This not helps too much, because low slew rate of first amplifier is magnified with low slew rate of second... and whole thing has too wide pulses for my taste.

		Quote:			Posted by {author}
	IN my coils (25 cm, 40 cm and 110 x 110 cm) I am using 1.3 m. stereo cable, without solder the isolation wire. Is this correct?

If coil is not shielded, it not make any change if you use stereo cable instead coaxial cable. Amount of interference is already too high. Especially indoor, during testing device (or close to high voltage power lines).

		Quote:			Posted by {author}
	Other problem: (sorry!) Can I change the BC's 546C BY 549C?

Yes, you can. That two transistors has the same small signal amplification.

		Quote:			Posted by {author}
	Thank you again, my friend! Best regards. Claudio

You welcome.

Regards,
m--

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P.S. Few days ago, I tried to use D7A opamp as differential integrator and got tripled sensitivity! But also more than tripled instability due to bad auto-tune circuit, and way how it process signal. Got to the point when further modification of DP has no any meaning for me. This PCB now serve partially as prototyping board, and learning platform. (I learned it hard way)

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