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Offline galaksiTopic starter
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« on: May 29, 2011, 04:39:13 pm »
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Simple metal detector with a CD4011

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Offline mikebg
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« Reply #1 on: June 15, 2011, 12:37:55 am »
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Cornelius sent in  topic "Discriminating BFO detector",  two different  pcb designs.

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I gave both pcbs in reply #76 side by side for comparison. The left figure was sent by Cornelius on November 09, 2009, and the right one - on December 13, 2009. Note that they have the same part number 909003-1-4.

"Cornelius, please dig your archives with information and found the circuit diagram and parts list valid for the left pcb. It uses PLL IC CD4046 in shown position instead conventional reference oscillator. Wait so eagerly that information from you!"

I'm waiting nearly one year without answer.
Galaksi, I think the text in your circuit diagram is in Netherlands language. If you have more old Nederland circuits for BFO, please search for a circuit diagram according PCB in left side.

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Offline Homefire
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« Reply #2 on: June 15, 2011, 08:46:37 am »
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There's another one out here some place that is crystal controlled on the Ref Osc.

I have it some place but cant find it.

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Offline mikebg
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« Reply #3 on: June 18, 2011, 11:46:52 pm »
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Homefire, the crystal controlled Ref Osc is not the best design solution, but please excavate your archives of BFO circuits and help me to fill my collection of frequency shift metal detectors.
See a thread started by me:

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Do you met a such principle of Ref. Osc.?


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Offline GoldDigger1950
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« Reply #4 on: June 19, 2011, 01:54:19 am »
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Homefire, like Mike says, you want a drifty old oscillator in a BFO not one locked to a crystal. The more drift you get, the better the sensitivity in the detector.

I've told you that before. Write it down this time, mate! Detention after class if you forget it again.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
Let's Talk Treasure!

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« Reply #5 on: June 19, 2011, 02:44:24 am »
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hi and its interesting can you please post the pcb etch and other layouts   

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Offline Homefire
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« Reply #6 on: June 19, 2011, 07:00:26 am »
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OK GD.   Please remind me why it's better to have to re tune the detector every 5 minutes here?

Here is the X controlled version:

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http://www.geotech1.com/pages/metdet/projects/eti561/eti561_300.pdf


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Offline GoldDigger1950
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« Reply #7 on: June 19, 2011, 12:54:48 pm »
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If you're serious, the answer isn't what you are pointing to. The drift I am talking about is not the overall machine drift but the beating drift between two oscillators. Without that drift, the BFO cannot possibly function well. A crystal defeats that drift. That model, while looking very cool and containing the author's opinion that a crystal is good, never did perform well and subsequent revisions removed the crystal.

Use a crystal if you wish. Your crystal BFO will not be as good as a cheap old BFO without one. The BFO is designed around the instability.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
Let's Talk Treasure!

Offline mikebg
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« Reply #8 on: June 19, 2011, 10:51:57 pm »
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What is the best circuit for search oscillator?
I showed in the Geotech1 forum, that it should have separate TX and RX windings and powerful amplifier with high gain, for example with LM386. Both windings are situated near to induction balance.
I started a topic as puzzle here in this forum, however nobody interested for best search oscillator. Sad

What is the best circuit for reference oscillator?
As was showed in this forum, it should operate as PLL circuit made for example with CD4046. The oscillator is slowly self-adjusting to zero beat frequency. There is a button for quick adjusting. When appears a target, there is alert because the Ref Osc can not set quickly beat frequency to zero. However the operator can set zero for exact pinpointing. Detecting

Cornelius posted the pcb for metal detector having such Ref Osc, but he has not posted the circuit diagram.

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« Last Edit: June 19, 2011, 10:55:34 pm by mikebg »
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Offline faycel
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« Reply #9 on: November 04, 2011, 03:48:40 pm »
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i dont thing its good beggining

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