Tiny Metal Detecting device? Magnetic Sensor?

Thread Starter

PaulHollingsworth

Joined Jan 13, 2016
20
Hi All, I was wondering today if it would be at all possible to make a tiny metal detector device, no bigger than an inch squared or even smaller?

I wouldn't know where to start in terms of the type of sensor that I would need, but it came about by an app on my iPhone, where you can utilise the magnetic sensor in the phone to turn it into a metal detector. It measures the magnetic field and alerts you when this increases to a significant value. Obviously, this isn't entirely accurate but is a good start.

Has anybody had any past experience with certain types of sensors that might be useful for me to play around with.

Many Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
19,394
Isn't metal detector and magnetic field detector two different sources?
But you mention the sensor is already in the phone?
(SMD is Surface Mount Technology).
There are magnetic proximity sensors such as the miniature Honeywell SS400 series.
Max.
 

ISB123

Joined May 21, 2014
1,238
This is THT(Through Hole Technology)


This is SMD(Surface Mounted Device)


Generally SMD's are smaller which makes it possible to construct smaller equipment like today's smartphones.
You can use NE555 and a coil to build a simple metal detector.
 

Thread Starter

PaulHollingsworth

Joined Jan 13, 2016
20
Excellent. Thanks for the info guys. This has given me something to start looking more into. I appreciate your patience to explain things to me as a noob
 

Pinkamena

Joined Apr 20, 2012
22
Well, magnetic field sensors (Hall Effect sensors) only detect magnetic fields, not the presence of metal itself. Metal detectors use a coil with an oscillating current passing through it, thus generating an oscillating magnetic field. When a piece of metal is introduced to this field, Eddy currents will be induced in the metal object, which then sets up its own magnetic field. It is this field that must be detected. I also believe it's possible to only use the inductor itself. When a metal object is introduced to its field, it will change its inductance. If this inductor is part of an LC circuit then the natural frequency will change, and this change can be measured. I believe this is how the "door style" metal detectors used at airports, for example, works. The benefit of this method is that you will not need the Hall Effect sensor.
 

MaxHeadRoom

Joined Jul 18, 2013
19,394
Well, magnetic field sensors (Hall Effect sensors) only detect magnetic fields, not the presence of metal itself.
Not quite true, there are many manufacturers of industrial Hall effect sensors that will detect a ferrous metal flag, you can even get proximity sensors for non-ferrous metal.
Others are designed to use a P.M. for detection, it is all in the design, but all are Hall effect in design.
Max.
 

ian field

Joined Oct 27, 2012
6,539
Hi All, I was wondering today if it would be at all possible to make a tiny metal detector device, no bigger than an inch squared or even smaller?

I wouldn't know where to start in terms of the type of sensor that I would need, but it came about by an app on my iPhone, where you can utilise the magnetic sensor in the phone to turn it into a metal detector. It measures the magnetic field and alerts you when this increases to a significant value. Obviously, this isn't entirely accurate but is a good start.

Has anybody had any past experience with certain types of sensors that might be useful for me to play around with.

Many Thanks
There was one in an old copy of ETI, but I downloaded them from both americanradiohistory.com and electronicsandbooks, so I don't know which that issue came from.

It used a single transistor and an untapped single winding inductor - but you have to use it with a pocket AM radio to pick up the disturbance in oscillation frequency.
 

Pinkamena

Joined Apr 20, 2012
22
Not quite true, there are many manufacturers of industrial Hall effect sensors that will detect a ferrous metal flag, you can even get proximity sensors for non-ferrous metal.
Others are designed to use a P.M. for detection, it is all in the design, but all are Hall effect in design.
Max.
Oh, that is interesting. So they come with built-in coils to generate eddy currents? I mean, it can't only be a hall effect sensor and nothing else.
 

nsaspook

Joined Aug 27, 2009
6,577
Oh, that is interesting. So they come with built-in coils to generate eddy currents? I mean, it can't only be a hall effect sensor and nothing else.
Yes they have an internal field generator. What's neat about them is they work at zero or very slow RPM unlike most variable reluctance sensors.
This is a Honeywell Hall-effect based notched wheel RPM detector being used to trigger a signal to emulate (with a PIC18F1320) the original reluctance sensor output from a much higher speed motor.
http://www.farnell.com/datasheets/1485997.pdf

In operation:
 
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