Looking for metal sensor

Hi, I am doing a project that requires my system to detect metal. What is the best metal sensor that I can use with my UNO board? I search up on google and found inductive proximity sensor and hall effect sensor. What are the difference between two of them and which one should I use? I could not clearly understand the difference between two of them from google search. I hope someone in this forum can answers my question. Thank you :smiley:

A hall effect sensor will detect only magnetic materials, or magnetic fields generated by electric currents. An inductive sensor will detect most electrically conductive materials.

jremington:
A hall effect sensor will detect only magnetic materials, or magnetic fields generated by electric currents. An inductive sensor will detect most electrically conductive materials.

Thank you for your explanation. Are there any suggestion for inductive sensor that would be compact and easy to use for my project?

Commercial inductive sensors are expensive. What is your definition of compact?

In my recent project I used inductive proximity sensors . They work really great. They detect all metals in the proximity range. I used 4mm sensors. They are very accurate and available at Rs. 250 in India ( £ 3) which is not expensive.

http://www.nskelectronics.in/inductive_proximity.html

I used 12V, PNP, 3 wire sensor . Connections are as follows

Brown - 12V
Blue- Ground
Green- Signal

Place a suitable resistor between Ground and signal . Due to current flowing in resistor, voltage develops. Put a potential divider and feed it to arduino.

Hope this helps ..

To interface it to arduino use a 7805 regulator.

No no no no no.
Never use a voltage regulator to reduce the voltage on a signal, that is just silly and causes you all sorts of problems.
It is like going out and buying a large book just to hold the door open.
It is the sort of thing beginners think of.

Use a two resistors in a potential dividor, or a transistor to get the signal to the right voltage.

I tried using resistor as potential divider. But that didn't work. Somehow it would give 12v at output. I found a regulator lying around. Although I have never used a regulator like that , this time I tried and it did work properly. So far no errors. If you could tell me the problems that I might encounter using a regulator there, I would be thankful to you.

I tried using resistor as potential divider. But that didn’t work. Somehow it would give 12v at output.

Don’t know what you were doing but what ever it was it was not right. A potential divider is a the answer.

I tried different resistors but voltage is always around 12V.

With a single resistor yes it will. A potential divider is two resistors in series and you connect the arduino across the resistor that goes to ground and give it a ground in common with the arduino.

So far no errors.

Have you looked at the signal on a scope? What about the rise time?

If you could tell me the problems that I might encounter using a regulator

The major problems are oscillations, instability, problems with minimum current draw and speed of propagation through the regulator.

krishnapatil:
In my recent project I used inductive proximity sensors . They work really great. They detect all metals in the proximity range. I used 4mm sensors. They are very accurate and available at Rs. 250 in India ( £ 3) which is not expensive.

http://www.nskelectronics.in/inductive_proximity.html

I used 12V, PNP, 3 wire sensor . Connections are as follows

Brown - 12V
Blue- Ground
Green- Signal

Place a suitable resistor between Ground and signal . Due to current flowing in resistor, voltage develops. I tried different resistors but voltage is always around 12V. To interface it to arduino use a 7805 regulator.

Hope this helps ..

Yeah, I was looking at this sensor also earlier. But it looks big for my system since I am building a small robot that can detect metal for this project.
What if I change my objective instead of looking for metal I want to look for a magnet. I did some research and found some smaller sensors such as digital magnetic sensor (Gravity:Digital Magnetic Sensor - DFRobot) and hall effect sensor (Shop by Category | eBay). Can anyone tell me the difference between the two? Which one is better or is there any other sensor that better for my project?

Thanks

The first is just a reed switch on a board, the second an electronic sensor.
The range of both is only a few mm.
What sort of range do you need?
You might be better off using an electronic compass.

Grumpy_Mike:

Don't know what you were doing but what ever it was it was not right. A potential divider is a the answer.

Yes, I was wrong. There was connection fault. Potential divider worked perfectly. Thanks for rectifying me.

Have you looked at the signal on a scope? What about the rise time?

No I didn't. I didn't notice the rise time. It would be in milli seconds. I was using induction motors in my project, It has inertia effect , so milliseconds didn't count much. But anyhow my approach was not right.

The major problems are oscillations, instability, problems with minimum current draw and speed of propagation through the regulator.

Yes, these matters much when using for a precision task. Thanks for correcting me.

Grumpy_Mike:
The first is just a reed switch on a board, the second an electronic sensor.
The range of both is only a few mm.
What sort of range do you need?
You might be better off using an electronic compass.

Thank for your response,

Which one is better the reed switch or the electronic sensor?
What I have in mind is to make a small robot, setup a closed course, and let the robot find a magnetic object and beeps and continue to find the next magnetic object. I am not really sure if I need to have a large range or short range sensor to do this.
Does electronic compass better and easier to use than the reed switch or electronic sensor?

Which one is better the reed switch or the electronic sensor?

They are very similar in terms of range, both have a range of about 3mm max which I suspect is a lot shorter than you were thinking.
The hall effect being solid state lasts a lot longer but we are talking of many years in this sort of application even for a reed switch.

I suggested a compass because the range would be greater but a lot more difficult to interpret. Basically it will be a point where the field changes rapidly and not in response to your direction of travel.

It depends what you are trying to do. Looking for gold nuggets ? Lost coins at the beach ? Nails in the wall ? Sorting garbage ?

You might find it useful to google "diy metal detector" and read some of those.

Grumpy_Mike:

Which one is better the reed switch or the electronic sensor?

They are very similar in terms of range, both have a range of about 3mm max which I suspect is a lot shorter than you were thinking.
The hall effect being solid state lasts a lot longer but we are talking of many years in this sort of application even for a reed switch.

I suggested a compass because the range would be greater but a lot more difficult to interpret. Basically it will be a point where the field changes rapidly and not in response to your direction of travel.

Yeah, it is shorter than what I was thinking of. For this project I want to build a simple system, such as driving the robot in a grid pattern with a closed setup course and beep when it detects a magnetic object. I am not to sure on if I can accomplished that easily with magnetic compass.
How will you drive a robot if there are a couple of magnetic object on the ground and having the robot to go trough each spot to beep without getting it to comeback to the spot that it already been? I think this will be great if I can understand the programming behind this as the robot will not have to go through a grid pattern that might take a long time to sweep the entire course.

The thing about using a compass is that you must also know where the robot is from other means, like inertial navigational. Therefore you will know what the compass should read at any point. When you find that the compass is giving a wildly off reading you know you are close to your magnet.

A conventional metal detector would also work for you here providing it is not disturbed by the motors.

as the robot will not have to go through a grid pattern that might take a long time to sweep the entire course.

That implies you need a much longer range with proportional sensing.

How will you drive a robot if there are a couple of magnetic object on the ground

To be successful, you are probably going to have to improve your understanding of what you are actually want to detect.
Magnets ?
Pieces of iron that respond to magnets ?
Other objects ( mostly metals ), which are electrically conductive ?

Grumpy_Mike:
The thing about using a compass is that you must also know where the robot is from other means, like inertial navigational. Therefore you will know what the compass should read at any point. When you find that the compass is giving a wildly off reading you know you are close to your magnet.

A conventional metal detector would also work for you here providing it is not disturbed by the motors.

as the robot will not have to go through a grid pattern that might take a long time to sweep the entire course.

That implies you need a much longer range with proportional sensing.

Thanks for the idea, but it seems too complicated for my little project. For the course, it will not be a big course. It is just going to be a small set up course with a couple of magnets, let my system to sweep the course and beep whenever it detect a magnet, and continue to sweep the course to find the next magnet.

michinyon:

How will you drive a robot if there are a couple of magnetic object on the ground

To be successful, you are probably going to have to improve your understanding of what you are actually want to detect.
Magnets ?
Pieces of iron that respond to magnets ?
Other objects ( mostly metals ), which are electrically conductive ?

Yes, I want to detect a magnet that I will put on the ground. The robot will have a ground clearance so that the magnet can go under it.

Can someone explain to me the difference between unipolar and bipolar hall effect sensor (non latching type)?
From what I know:

unipolar = turns on when it detects north pole and do not do anything when it detect south pole (or the other way around).
bipolar = turns on when it detects either north pole or south pole.

Can someone clarify this or correct me if I am wrong.
Thanks.