Metaldetector

[Smartsword]

Metal detector:
I have an urgent question!!
Like the video in the link:
The copper wire has two connections...But only PIN2 is shown in the video?!?

How i connect the two end of the wire?

 

[Smartsword]

I Need a Transistor npn normaly closed!
What Typ Name/number?

 

[audioguru]

I Need a Transistor npn normaly closed!
What Typ Name/number?

A door opens and closes. A transistor turns off, or turns on partially (is linear) or turns on fully (is saturated).
There are thousands of different transistors because:
1) Maximum allowed voltage.
2) Maximum allowed current.
3) Maximum allowed dissipation (heating).
4) Maximum radio frequency.
5) Lowest maximum noise (a good signal to noise ratio).

Normally closed?
An idle bipolar or enhancement mode Mosfet transistor are turned off and does not conduct.
A bipolar transistor is turned on when it has base to emitter current which needs some base to emitter voltage.
A depletion mode Jfet is turned on when its gate to source voltage and current are zero.

 

[Smartsword]

Is that Transistor bc557b normaly closed?

 

[Pommie]

You appear to think that transistors are similar to relays with NO and NC contacts. They're not. They will turn on (collector and emitter connected) when a current flows into the base. See wiki.

Mike.
Edit BC557 is a PNP transistor.

 

[tepalia02]

Instead, you can buy a KY-036 Metal Touch Sensor Module and make an Arduino-based circuit with it to make your metal detector.

 

[Smartsword]

Does the metal contact still work if I extend the middle pin by about 1m as marked in green and then touch it at the front?

 

[Smartsword]

Like that

 

[rjenkinsgb]

It would probably trigger all the time indoors or near any AC mains power; outdoors would be hit and miss.

It's a simple "Touch switch" type device, not actually a metal detector.

I think it works on hum pickup, like touching an open input on an amplifier.

 

[Smartsword]

The length marked in green of approx. 90cm is an ISOLATED cable as an extension of the middle pin, which is not insulated at the end and comes into contact with metal there!

would it work like that?

 

[rjenkinsgb]

I think you mean "insulated"?
Insulation does not block capacitive pickup.

I've found an article that shows the module schematic; it is just a "hum detector" type device as I thought.
Anything that acts as an antenna connected to the input pin (transistor base) and picks up enough stray signal will trigger it.
(And insulated wire is fine as an antenna).

KY-036 Metal touch sensor module - EasyEDA open source hardware lab

In EasyEDA open source hardware lab, open source square pools all kinds of electrical design engineerings together to realize resource sharing easily.

oshwlab.com

The effects of connecting wire to it will depend on the local electromagnetic environment.

 

[rjenkinsgb]

and comes into contact with metal there!

Also note it is a very crude touch switch not a metal detector! Anything conductive may trigger it - including damp materials or skin. If both you (holding it) and whatever it touches are at the same potential, it will not be triggered.

 

[Smartsword]

yes isolated

But there has to be direct contact between the base (antenna) and metal to trigger it so that it triggers a touch signal?!
Is it possible to adjust the sensitivity ev with resistors so that the stray signals are too weak to trigger the sensor, i.e. only if there is direct physical contact because then the capacity is much higher...???

 

[rjenkinsgb]

But there has to be direct contact between the base (antenna) and metal to trigger it so that it triggers a touch signal?!

No - touch it with your finger and it will trigger. It is NOT a "metal detector", that's what I keep trying to stress.

Anything conductive may trigger it, dependant on the surroundings.

Actual metal detectors use inductive sensing, with a coil driven by an oscillator and circuitry to detect the changes that being near metal has on the coil / magnetic field properties, not capacitive or hum pickup.

 

[Smartsword]

one more question:

If only a metal part without physical contact is touched with the base, is there a signal? or does there always have to be physical contact?

 

[rjenkinsgb]

It senses electrical contact with anything conductive, that is not connected to the same circuit ground at the module, and is picking up "hum" or electrical noise from the environment.

Small, otherwise unconnected metal items would have no effect. eg. Coins.
If you were holding it and touched it to the base terminal lead, it be like touching it directly with your finger.

A large piece of metal or moderately long wire, that could act as an antenna touched it, that should also trigger it.


Anything that would cause strong hum or buzz if touched to an audio amplifier input should trigger it. Things that would not cause hum will not trigger it - as it works by sensing that same "hum" or buzz, just in a very crude and simplistic manner.

 

[Tony Stewart]

CW = clock wise , pointer(2) goes from pin 1 to 3 (123) at max CW 2~3 is about 5% of fixed R between 1-3 and max CCW, 1-2 is 5% and 2-3 is 95% of R.

But your coil is far too small to detect much metal. You are better off to get a ferrite rod AM antenna and use that.

 

[rjenkinsgb]

But your coil is far too small to detect much metal

If you look at the original [supposed] metal detector, it's just a floating wire connected to the 555 trigger pin.

It's triggered by a combination of chance and static or noise pickup, not by proximity to metal.

 

[Smartsword]

Hi

I only want to have the analog output of this metal body touch sensor ky-036 without LED.
What can I leave out of the diagram so that the sensor still works but can do without digital components?!...
Maybe you can mark in red what I can leave out

 

[Smartsword]

Hi

I only want to have the analog output of this metal body touch sensor ky-036 without LED.
What can I leave out of the diagram so that the sensor still works but can do without digital components?!...
Maybe you can mark in red what I can leave out

 

[alec_t]

Just leave out any connection to the DO output.