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Simple Metal Detector Circuit Keeps Beeping - Help

itpelecnewbie

Apr 17, 2018
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My daughter created a simple metal detector circuit using an example from the internet with the components listed below. When she attached the battery it keeps beeping, and when any metal is placed around the coil the frequency or level of the beep does not change. What is wrong with the circuit (see picture attached). I appreciate feedback on how to get this to work. Thank you

image.jpg

- breadboard
- resistors: 1k, 100R, 330R
- buzzer
- TDA0161
- 10K Ohm Trim Pot
- NPN Transistor 2N2222
- Single Polyester Film Capacitor (470nF - 470uf) 1nf
- High Voltage Capacitor Radial Lead - 47nf
 
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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Perhaps you could post the circuit?

It is possible that you have wired it up incorrectly or that the stray capacitance of the prototyping board is meeting things up.
 

kellys_eye

Jun 25, 2010
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That looks suspiciously like UN-enamelled copper wire making up the coil - it's also very 'thick' wire. What are the specifications for the coil?
 

itpelecnewbie

Apr 17, 2018
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That looks suspiciously like UN-enamelled copper wire making up the coil - it's also very 'thick' wire. What are the specifications for the coil?
It’s 26 - 30 AWG wire of 150 turns of diameter 5-6 cm. I think we purchased the wrong one. What would you recommend?
 

Chemelec

Jul 12, 2016
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The picture is posted.

Can you Post Your SCHEMATIC?
The TDA0161 is a Proximity Detector and Only detects for a Very Small Distance. (Possibly for 1 Inch)
Also the Coils is Supposed to be wound on a Ferrite Rod.
 
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hevans1944

Hop - AC8NS
Jun 21, 2012
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The picture is posted.
In this case, a picture is NOT worth a thousand words. Your picture is almost worthless in understanding what your daughter has cobbled together. What @(*steve*) requested was that you post a schematic diagram, NOT a picture of a jumble of wires and barely visible, value unspecified, components on a breadboard. That picture is worse than a Fritzing image, and those are pretty damn useless except for "monkey see, monkey do" activities.

If you really want our help here, please post a link to where you obtained
a simple metal detector circuit using an example from the internet
And if the link doesn't contain a schematic diagram, perhaps you can draw us up one by hand, photograph and post it? Or maybe your circuit is a variation on this one (copied from this blogspot post):

TDA0161%2BMetal%2BDetector.png


@kellys_eye: at first look I thought the OP was using bare copper wire. Typical newbie mistake. It is almost impossible to tell from the picture whether the wire, which appears to be stranded, is covered with a clear plastic insulation or not. The soldered connections to the breadboard wires also look a little hinky. But the worst thing is this a an oscillator running at about 10 MHz. The 2005 datasheet from STMicroelectronics for this, now obsolete part, says "When using Litz wire instead of single wire, the parallel resistance of the coil becomes higher and value of R1 may be increased, resulting in better sensitivity."

There are several You Tube videos demonstrating this circuit. It appears to have a very short, probably not a practical, detection range. Mainly useful as a proximity detector, although Hall-effect devices do a much better job if you don't mind having to use a small magnet as the proximity target.

Kaman Nuclear (now Kaman Precision Products) used to make and sell a similar proximity detector, based on eddy-current induction in an aluminum (typically) target in the 1960s. It was a linear device that provided a precision analog output signal representing distance to the target.

The ST application notes indicate a ferrite pot-core was used as a coil-form to wind the coil for the TDA0161 in various sizes, but it doesn't indicate whether the ferrite was left in place after winding the coil. I doubt whether it was because that would increase the inductance a lot and concentrate the magnetic field to the nearby vicinity of the coil. Most of the videos I have seen use an air-core coil, which "feels" about right for a hundred or so turns about two or three inches in diameter to resonate at somewhere between one and ten megahertz. An oscilloscope would be a big help in getting this contraption to actually work. Stray capacitance plays a huge role with this type of circuit at these MW radio frequencies.
 

kellys_eye

Jun 25, 2010
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Looking at the breadboard layout I can see the white wire link (from one of the coil wires) isn't connected to anything.......

similarly, if the copper wire DID have an enamel coating there would be signs of it where the wires are soldered to it - I can't see anything.
 

Chemelec

Jul 12, 2016
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It Looks like Enamel Coated, Just a Light Color Coating.
I have some like that.
But Yes that one white wire is in the Wrong Hole.
However, It will NEVER Work with that type of Coil.
It Must be wound on a Ferrite Rod or Pot Core With the Correct Inductance Value.
As per the Data Sheet.

Detection Range (*) L1 (mH) C1 (pF) fosc


(kHz)

R1

(k
W)


C2

pF

2mm 30 (1) 120 2650 6.8 47

5mm 300 (2) 470 425 27 470

10mm 2160 (3) 4700 50 27 3300
 

73's de Edd

Aug 21, 2015
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Sires . . . . .

In contributing a BIT of visual enhancement upon that proto breadboard board . . . . . . now you are able to be a much better examin - OR while it do be the examin - EE . . . .deah, Andy.

This seems to be the closest unit to be compared to, that is using that selection of parts values.

Its whole write up is here . . . .

https://www.electronicshub.org/metal-detector-circuit/


The YELLOW ovals are definite errors, where only one lead of the inductor gets connected into circuitry.
That wire size is looking like #18 or possibly 20 to my trained eye gauge.
If I give it credit to it as being enamel insulated, I still don't see the beginning and end of wire soldered connections.
I can see YELLOW A making its proper connection into the Br Bd but Yellow B seems to be the only connection of that 5 conn tie strip.
With that whole coil about to go SPROOOOOING and come apart, two 180 or four 90 degree ties migh be in order, by using some binding twine.

NOW . . . . .what is that being used for the almost two side by side round binds . . . .twine, with it being permissible, OR . . . is it being hook up wire or solder braid that completely encircles the inductor and is making two shorted loops around it?

I still can't see some of the hidden connections for confirmations.
But . . . . the incoming power wires are improperly color coded, and 5VDC supply definitely might be a bit low for that chip...

ENHANCED VISUAL REFERENCING:

Metal_locator_Ckt_Enhanced.png


73's de Edd
.....

 

hevans1944

Hop - AC8NS
Jun 21, 2012
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@73's de Edd: Bit of nice detective work there! Unfortunately, the only feedback we have received from the OP, @itpelecnewbie, has been the rather terse and uninformative comment: The picture is posted. Some of these newbie posters are incomprehensible in their attitudes. For someone who is asking for help, they are not themselves very forthcoming with details. IMHO, this type of poster is a friggin' total waste of time (FTWOT)... and probably a "drive by" poster, too, seeking only a quick answer, not knowledge or discourse. Humor them at your own risk, but remember: Life is short. Eat dessert first.
 
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