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Post by Gary Lecomte on Mar 23, 2015 15:36:40 GMT -8
Sorry, 3c90, I Don't know What that rod is. That is a Very Small Diameter, so it will Pin Point Very Accurately, But Detection Distance for Coins Will be Shorter than a Larger diameter rod.
I would try about 180 turns for L1 and 60 to 80 Turns for L2.
If it Won't Oscillate, Make sure you have a Correct Polarity on the Coils. You may also Increase the value of the 5K Pot to 10K or 25K if the coil is too far out of range to oscillate.
The Exact Frequency isn't Important, But the Higher it is the Greater the Sensitivity to TINY Objects. Most of mine are oscillating in the 250 Khz to 350 Khz.
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Post by lamazoid on Mar 24, 2015 3:53:49 GMT -8
i made the coil, and on the Q1 collector i have 357kHz 3v amplitude clear sine wave oscillation. but it seems to be no reaction on metal objects at all
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Post by Gary Lecomte on Mar 24, 2015 6:18:37 GMT -8
Since it IS Oscillating, The Coil and that part of the circuit is Correct.
Using the two Controls, You should be able to tune it, So it Just Barely Stops Oscillating. At that point, the LED should light.
Now if you re-adjust the fine tune control, so Oscillator Comes back on and the LED just goes off.
It Should NOW Detect Metal.
If Not, you may have a problem in the circuit.
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Post by lamazoid on Mar 24, 2015 8:02:24 GMT -8
i got it working by picking up a resistor in Q1 emitter chain (including POT resistor value) to around ~12k. this is the point when it stops beeping and flashing by itself, and starts detecting metal. when distance to coin changing, sound and flashes rate also changes, just like your description. but i got VERY LOW sensitivity (despite your description says it is very high) - it detects large 3cm coin from max. 15-20mm where should i dig to?
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Post by Gary Lecomte on Mar 24, 2015 18:17:16 GMT -8
A FINE TUNE IS CRIRICAL, Just at the Point of Change. A 250 or 500 Ohm or 1K, TEN Turn pot is needed.
And Like I said, Your Ferrite Rod is Pretty Small Diameter. Smaller Diameter is LESS DETECTION Distance.
The Smallest Rod I use is 8 mm. Most are 12 mm Dia.
You could Bundle and tape 3 Rods together (in Parallel) and wind your coil on them.
Also You may need to run the circuit for One Minute to get Best Stability before trying the Precise Adjustment.
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Post by lamazoid on Mar 30, 2015 8:06:22 GMT -8
i have rewound the coil using 8x50mm ferrite from AM radio antenna. 180 turns L1 and 75 turns L2. sensitivity is EVEN MORE DECREASED which of your coils on this photo: chemelec.com/Projects/Metal-Pin-3/PinPoint-3.jpghad best detection distance?
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Post by Gary Lecomte on Mar 30, 2015 15:02:32 GMT -8
Both the 9 mm and the 12 mm worked good, But I also made Many others with 8 mm and 9 mm rods that were good. I doubt an antenna rod is very good. The Ferrite rods I have are all a 77 Material, which is mostly used for power applications. You might consider this Pin Pointer Detector by NUPI,. www.geotech1.com/forums/showthread.php?21373-Can-pinpointer-detecting-thin-chain/page10There are 22 Pages in this article, but you probably need to JOIN this Forum, to see schematics.
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Post by lamazoid on Mar 30, 2015 22:17:18 GMT -8
The Ferrite rods I have are all a 77 Material, which is mostly used for power applications. ok, i'll give it a try with power ferrite. and what about geometry of the coil? some of yours wound layer-by-layer (secondary over primary), and some are "sectional" style (secondary NEXT to primary), how it reflects on device performance?
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Post by Gary Lecomte on Mar 31, 2015 6:17:31 GMT -8
Did Not make any Difference
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Post by lamazoid on Mar 31, 2015 8:21:45 GMT -8
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Post by Gary Lecomte on Mar 31, 2015 10:30:02 GMT -8
Yes that is NOT very Good, but I don't know what else I can tell you.
Are you using a Relatively LOW Resistance, 10 Turn Pot to adjust it? This adjustment is Quite Critical.
Some Inductance Values for my coils were L1 = 925uh and L2 = 144uh. Other ones were L1 = 2 mH and L2 = 160 uH. But they all worked pretty good. Definately MUCH Better than what your video shows.
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Post by lamazoid on Mar 31, 2015 10:57:04 GMT -8
Are you using a Relatively LOW Resistance, 10 Turn Pot to adjust it? This adjustment is Quite Critical. . no. i'm using 47K pot, but i'm able to find the point, when it stops oscillating. i'll try with lower value pot...
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Post by Gary Lecomte on Apr 1, 2015 5:55:18 GMT -8
It is MOST IMPORTANT to have a relatively LOW Resistance, 10 Turn or 25 Turn Pot for the Fine Tuning. Preferably a 1k or even just 500 Ohms. On one of my units, I used a 1K, 10 turn Trimpots, with an Extended Shaft so I could put a Knob on it for easier adjustment. Unfortunately these Trimpots are Not ment for continuous long term use.
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Post by slymn03 on Mar 7, 2020 11:02:51 GMT -8
there is a problem in my pinpointer piezzo is constantly singing is this right?
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Post by volkswagenvan on Mar 7, 2020 13:34:16 GMT -8
Hi slymn03.
I don`t think it should be oscillating / singing. Looks to be an adjustment problem or at the worst a circuit problem. I never built one. perhaps lamazoid or retiredat55 can lend a hand.
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