Weak Magnetic Field Sensing

Hi christopher,

With a Hall sensor you can measure distances. Here is a 2 ways to do this with high precision:

(1a) To measure a distance to a non-magnetized but magnetizable metal like iron etc: Mount a strong magnet on top of the sensor and move the object to meaure to measure to and from this sensor-magnet combination.

or

(1b) To measure the distance to a magnet: Only use the sensor, nothing else mounted. Here you may use a sensor that is more sensitive, all depends on the distances and magnetic fields you want to measure.

then measure it:

(2) Measuring the magnetic field: It must be a sensor that can handle larger fields like the Infineon KSY10, KSY13, KSY14, KSY44 (we sell those) or other ones. Let a current of 5 mA run through the inputs (you can also do it with a voltage, but a current gives more linearity and better temparature behaviour, all depends on how precise it must be). You can now measure the resulting magnetic field that is influenced by the distance. With a strong magnet, the output will get something like 100 to 250 mV at a very small distance and very low at a large distance.

Feel free to ask me any questions at: snipped-for-privacy@hoeben.com (without the NOSPAM)

Pieter Hoeben

I am not sure how far will these go

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

Keep in mind that once you get into the far-field region (ie, farther from the magnet than a few times its length) the field strength will drop off with the cube of distance, which is pretty severe.

I'd guess that it will be difficult for a Hall sensor to give you much signal 8" away from a "small" magnet. You might try it with a compass first to get a feel for magnitudes.

John

By AC excitation, the sensitivity of a Hall element can be enhanced by a few orders of magnitude. Lookup the term "lock-in amplifier".

Rene

Yes- but you will want to use a sensor + PIC/STAMP/uProc combination for calibration and linearization. Analog is largely a joke in applications like this.

In article , Boris Mohar wrote: [...]

The Zetex and Honeywell MR sensors generally out perform a NVE one. If the magnet in use is a "cow magnet"[1], you could get a detection range of about 20 feet. This assumes you are working far from any magnetic sources and that the magnet it turned end for end.

Hello Everyone,

The mean ones have not chewed me out yet so what exactly am I trying to accomplish?

Finding the best method using any type of sensor or effect for a non-tactile, hand controlled volume attenuating circuit. I just need to know what sensor would work best, I will design the support circuit.

Ken Smith !!! I do have a "cow magnet" which is chrome and about the size of my little finger, how did you ever guess that one? I only learned of these this week.

I am attempting to turn my "hand" into a human potentiometer with at least an 8" sweep range. I thought holding a magnet could give me a usable effect or force to do this.

I want to explore a new volume control method of a special musical instrument called a "Theremin". The normal theremin volume method uses a antenna and detects the shift in frequency of two perfectly balanced oscillators. It has very wide physical sensing area of more than one a foot diameter. Placing my hand out 12" then moving it next to the control antenna quiets the volume without touching it.

Yes, I can do the above technique, along with an optical method and a mechanical balance of two magnets opposing one another method which works but is not responsive enough and is sloppy.

I want to use a different approach that will have a working width in free space of about a 4" to 6" diameter and have detectable downward sweep range starting at least 8" to the outside, then have a controlled measurable output as my hand magnet moves down to the control sensor pickup.

This will allow me to have more than one (maybe four) sensor/detector spread out in the original one foot diameter or musical volume control panel area of which my hand approaches.

Non of the above values or measurements are critical and could be modified to adapt to the approach.

I have a webpage I show hobbyists/musicians how to build my theremin design and this volume control method would be a great enhancement.

"The theremin is the only musical instrument played without touching anything." It has can sound like a musical saw or an angels voice.

This is Clara Rockmore Circa 1940 .mp3 777kb

Thank you, your ideas are greatly appreciated.

• * * Christopher

Temecula CA.USA

In article , Christopher wrote: [....]

My spies are everywhere.

BTW: Either you've got a big little finger or a small cow magnet there.

Did this 10 years ago with a friend, using ultrasonics

martin

At 8" you need a sensitive sensor. But that may saturate at 1".

Pieter

...

Use LDRs (or PHDs or PHTs) and make a lumemin. A google search says "Popular Electronics, April 1955", but the link is dead. )-; Maybe someone has a copy of that issue. (yeah, right!) ;-)

You can still use your bare hands, and there's no RF.

Good Luck! Rich

Honeywell do a magnetoresistive sensor that has 2 bridges at 90 degrees, so it should be easy to make it sense a magnet waved around.

Paul Burke