Instructables

Magno-Sniffer (Magnetic Sniffer Probe Whistler Thing Using A Hall Effect Sensor)

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Working with magnets and want a fast way to tell their NORTHs from their SOUTHs? Want to get an idea of their field shapes? Like making weeeeeeeooooooeeeeeeoooo noises?

Build a Magno-Sniffer using a hall effect sensor, 555 oscillator circuit, piezo speaker, tongue depressor, hot glue, and a few other doo-dads.
 
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Step 1: Whatsit Do?

It makes an annoying tone that changes pitch when the sensor sees a magnetic field.


Step 2: Disclaimer

This assumes...

Some knowledge of electronics and soldering.

Safe handling practices for ESD (Electrostatic Discharge) sensitive devices like the CMOS 555 or flagrant disregard thereof.

Step 3: Circuit Chunks

Picture of Circuit Chunks
Hall Effect Sensor - A sensor that changes it's output voltage when it sees and changing magnetic field. They used to be expensive and complicated, but now they are simple and cheap.

VCO - Voltage Controlled Oscillator. A circuit that oscillates (makes a tone) at some pitch. The pitch changes when you feed it a changing voltage from the sensor.

Piezo Speaker - Changes the electric signal from the VCO to an annoying audible tone.

Battery, Regulator, and Switch - 9V battery power is reduced to 5V by the regulator because this hall sensor doesn't want to see more than 6V power. Pushbutton switch switches power like switches do.
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geq11 year ago
Hi! I made it, but it only reacts to one side of magnet. Have you got any ideas why? Thank you very much!
MagicTK geq11 month ago

What Hall sensor did you use? If you used the Allegro A1301 or A1302, it should work well for either pole. However, if you used a different sensor, some are only triggered by one pole or the other and have no output if the other pole is detected.

MagicTK1 month ago

I like this instructable a lot. I have made a very simple one with a Hall Effect switch and an LED just for any magnetic field, and I've made an adjustable sensitivity version with a Hall Effect sensor and two comparators one for N and one for S so I could set specific thresholds. However, I haven't made an analog version like you have here. I will be making something like this soon, I think. If I do, I might consider adding something like this Mini Digital Volt Meter https://www.adafruit.com/products/705 on the output, or even this mini oscilloscope http://www.gabotronics.com/development-boards/xmeg...

Does anyone know the purpose of R3 in the schematic?
It is a pull up resistor, it keeps that connection to near 5v so not to accidentally trigger the 555 ic while R4 prevents damage to the sensor when we raise this pin manually with R3
arduinoe5 years ago
you should magnetize your dog ... they say blood contains iron lol
Jodex arduinoe5 years ago
I could actually do that on my finger =0 I have some tiny piece of metal in my finger, witch MAY be from a Dremel's wire brush... But I am going to a surgery pretty soon and they will remove it.. I just realized once when I bought couple of neodymium magnets and they stuck on my finger =D
arpoky Jodex4 years ago
Sorry to bump this, but...

It could be some sort of ALIEN implant doohickey! You has been abducted by aliens!

Crap, I forgot to take my pills...

Trololo.
Jodex arpoky4 years ago
Yeah, that's what everyone says. They took it off my finger almost a year ago, and the little metal wasn't definately a wirebrush wire. Looked a bit like some seed or something. Still don't know how the heck it got there and how long has it been there, and what it is.
Hey! Nice 'ible!
I've got a 4 pin hall effect sensor. Will it work for this project?
rac5 years ago
dude, those resistors look older than me 8D nice 'ible though, i paid $40 for my sensor 8(
Aeshir7 years ago
Your dog looks like my friend's brother xD
tinkerC Aeshir5 years ago
Then punch your friends brother, only dogs look cute like that.
vinodkp8 years ago
Nice Dog. Not so good idea, there are better magnetometers out there, hall effect device is costlier then these.
tinkerC vinodkp5 years ago
Where.
static vinodkp7 years ago
That's not right. Telling us there is something better, then failing to tell us about it. Not constructive at alll.
static7 years ago
Far out instructable. Do you have any video showing reacting to magnetic fields other than the horse shoe magnet? Depending on projected cost I make one to give mt sister's kid to drive her nuts with.
tinkerC static5 years ago
Do that. Put one in her shoe, or the sole of her shoe. That will really drive her nuts.
offlogic7 years ago
A great instructable! I work with magnets daily, it's a useful gadget, and a nice dog in Step 12.
What used to be in 12? Show your dog after the sensor goes off. Or does the dog chew the sensor, so that doesn't work?
Lil Bastard8 years ago
I'm tired of everyone talking about how he's gonna win the magnet contest. Just wait till you see my instructable. It's gonna be called, "How to stick a magnet up your butt". It's gonna be AWESOME!!!!!
This coming from someone who hasn't posted any instructable as of yet. Sorry, but I don't go around shoving things up my butt like you do and I'm certain no one wants to see you do it, so I guess you lose.
Really lost far.
Perv.
Ewww...
oooh magnet a*s LOL
YUK! IMHO dogs are disgusting.
it would be interesting to do the computer equivalent of that experiment with iron filings by using a hall Sensor in conjunction with a positioning system to map a magnetic field in 3d.
Yes i was thinking the same thing. Combine a Hall effect sensor with a 3D positioning system such as those used by 3D printers.

Howard Johnson explains about this in his amazing book Spintronics -The Secret world of Magnets. There is information on page 31 on how they mapped the 3D fields.

Have you ever wondered about:How magnets work?Why some elements are magnetic and others aren't?How a magnet manages to change things without touching them?This book may suggest at least partial answers to some of these questions. But most likely there will still be more questions than answers, for there are many things still to be discovered about magnets.More work needs to be done. Maybe YOU will do it if you get inerested in magnets.
Howard Johnson, Spintronics

In other words, who will be first to create an instructable for a 3D magnetic field mapper?

Damn, I love this site.
You wouldn't need a full on 3D positioning system like that. Just get an old plotter from a garage sale and hack it, add an output for the hall effect sensor. Now thats not a bad idea... im actually gonna do that, I have an old plotter... Expect one from me within next 2 or 3 months
5Volt7 years ago
The kind of three terminal hall sensors you use can be found for free on scrap PC heat fans. The pin arrangement can be found inspecting the fan's electronics before removing the sensor. I like your implementation. 5V.
JordanZed8 years ago
I love this. I don't really need one but I think I'm going to make one anyway.
MrMunki8 years ago
Very nice. Really well written. I especially like your schematic.
Have you thought to adding in a meter to tell how strong and which direction the magnets are?

Such as this:
http://www.web-ee.com/Schematics/GaussMeter/GaussMeter.htm

I think yours looks much more compact and neater though, but maybe adding two terminals on it to test out the strength will make it even better.

Hall Effect Sensors can be found here for anyone interested:
http://www.lessemf.com/dcgauss.html
thanks for posting that... I've been looking for a simple gauss meter :p
pronteon (author)  FrenchCrawler8 years ago
All good ideas. I think I will add terminals for a meter. Thanks.
Or you can just get the samples from his 4th step :D
VIRON8 years ago
Something's missing in this picture. Oh, you forgot the magnet! Here it is:
http://www.hfml.ru.nl/froglev.html
MrCakes148 years ago
Just a quick question - does the 555 have to be CMOS, or will any 555 (or 556, if you need two for some reason) work? As they are in fact different (slightly). Also...incredibly excellent (and amusingly annoying) project; very clever!
pronteon (author)  MrCakes148 years ago
The pin 5 input on a regular 555 takes a lot more current. So I don't know if the sensor could drive it. Might be fine if the 2 resistors on pin 5 were lower? Don't know. Thanks!
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