XR71 Operation Help

		Quote:			Posted by fathertime
	LOL ...I have no idea what all that means, but thank you. I have alot of free time, and and almost uncontrolable desire to assemble things so that will work out for me.

If you made decision to make one simple but relatively good detector, rather find Diagram of the "Hammerhead" (by Carl Moreland, revision 1.5 - 21 July 2006) PI MD.

Also, I suspect that this diagram has one (maybe minor) error: R16 of 1 MOhm should be connected to non-inverting input of the IC6 not at pin 2 (inverting input). I have that .pdf document, only revision 1.5. Maybe later revisions are corrected, don't know.

I made Delta Pulse, not because it is simple, but because at first look it looked more promising. Now I have bad taste in my mouth, and will consider to make my own hybrid - utilizing the best parts of various circuits.

This is my first DIY PI MD project (long time ago I gave up of making BFO MDs), and I may consider it as a learning platform only - to see how it behave, and what which part should to do, or how it actually works. Many sleepless night and infinite o-scope tracing lead to conclusion that this unit works 'somehow', but I believe that it can perform much better.

In Delta Pulse circuit, there is covered all basic principles, but not so good realization. Out there is another attempt of modification of this circuit, such as DBP 2010, but it has the same problem with scrambled circuit.

So far, Hammerhead is the best learning platform, considering relative small amount of parts and lower cost.

Regards,
m--

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Sweet thanks for the info.  Do not want to start something and give up on it later.  So i will check out the Hammerhead. 

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		Quote:			Posted by raff33
	hello, can you put here your final modification(changed parts).......... and how deep can detect your detector with excellent stability ? Regards.............raff33

Well, stability is about self tuning or auto tuning. Not about increased sensitivity.

R29 was 1M - should be 22k,
R34 was 22k - should be 1M,

That two is replaced, and now at pin 3 of opamp D7A come strong pre-pulsing signal from Tr2 for auto tuning. To filter it, put one electrolyte of 1 uF - pin 3 positive end, ground negative end. This will filter out signal from Tr2.

Also, threshold worked at bad point - it show signal on uA-meter, but no sound. To fix that, instead jumper between tap of potentiometer "threshold" and base of transistor T9 (BC557) put resistor of 6k8, and instead resistor R41 (was 6k8), put 2k2 resistor.

This button "reset" or "tune" on some diagram works for both functions: quick set in range for auto tuning circuit, and for battery check. With that change, battery check work without difference, but signal peg scale when threshold is set to maximum sensitivity (CCW).

Since that changes, no more need to push reset button after turning on MD. It quickly get to working point and only sounds when metal change position in respect to coil. Once close to metal, sound cease and if more close to metal, it sounds again. When metal is removed, auto tune back relatively quickly to proper operational point.

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Side note:

Instead LF356/7 there can't be applied any other operational amplifier as is NE5534 or LM318 because last two are not JFET opamp. Operating point is close to +E rail and only opamps with JFET input can manage such case. That is because there is compromise in circuit not utilizing additional DC/DC converter to get +5V above +12V of the battery, so that +12V is actually connected to ground as is in many other MDs. Any operational point close to +/- rails are bad point for operational amplifiers, but... eh... It is as-is, and we should live with that.

Regards,
m--

		Quote:			Posted by fathertime
	Sweet thanks for the info.  Do not want to start something and give up on it later.  So i will check out the Hammerhead.

Well, Hammerhead's circuit is not without errors. Actually I not found any circuit without some errors or need for some improvement. Currently looking at Goldscan 4 circuit. It is very challenging circuit, and there also exist few errors.

It utilizes J113 JFET, but on PCB - there is gate at wrong place for that transistor - in the middle instead at one end. So, I think that there may work 2N3819 JFET. Also, two transistors in power supply are not 2N3904 and 2N3906, but rather BC546 and BC 557 - emitters are at wrong place because that two kind of transistors has different pinout (swapped emitter-collector positions). Two clamping diodes 1N4148 should be anti-parallel, and not in the same orientation as is in circuit.

Instead NE5534, there may be used LM318 - better slew rate (NE5534: 13V/uS, LM318: 50V/uS), but I think that relatively cheap NE5534 may work nicely.

Also, in circuit, there is mentioned pulse width of 10 uS, but calculation of RC components clearly show ~260 uS pulse width.

With working frequency of 450-550 Hz and such wide pulses, battery will be very soon empty. Also, battery is not 12V but 14.4V. So, we can't use lead acid battery for UPS purposes. Aside that, it is difficult nowadays to find germanium diodes OA85 or similar.

I like small PCB of Goldscan 4, but serious drawback is using SMT components on bottom layer of the PCB. Many people can't afford that, or it is pain in the neck to solder. Also, PCB has very thin stripes, so it is very challenging to make photoresist and etch copper without destroying that stripes.

I think for first project, it is better to make simplest as possible circuit - less time consuming and less frustration. One simple diagram is "Underwater" PI MD. It is made for pinpointing gold with ferrite coil (at least I saw some one made ti that way), but coil may be scaled to big one (air core) and working on treasure hunting.

Regards,
m--

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Seems to me that reply is not easy at this forum to someone who post earlier than last post. When quote or reply, it add all posts in one... Bad thing.

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if you ar eli you dont need metal detector too find a gold   

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hello Powerlab,
many thanks for informations  I hope this help ......... proplemes with DP i will do....................
please to put here picture after completing all parts ( final MD ) for helping who has'nt good experience in electronic.
Regards.....raff33

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