Step 5: Schematic

I drew this from looking at the finished sniffer that I built a couple years ago. I hope it's right.

C1 - .01uF (sets pitch, larger value = lower pitch)
R1 - 100k (also sets pitch, larger value = lower pitch)
R2 - 10k or so
R3 - 22k (or 2 10k's in series)
R4 - 10k
C2 & C3 0.1uF but not critical, probably anything 0.01uF to 1uF would work.
Hi! I made it, but it only reacts to one side of magnet. Have you got any ideas why? Thank you very much!
<p>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.</p>
<p>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 <a href="https://www.adafruit.com/products/705" rel="nofollow">https://www.adafruit.com/products/705</a> on the output, or even this mini oscilloscope <a href="http://www.gabotronics.com/development-boards/xmega-xprotolab.htm" rel="nofollow">http://www.gabotronics.com/development-boards/xmeg...</a></p>
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
you should magnetize your dog ... they say blood contains iron lol
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<br />
Sorry to bump this, but...<br><br>It could be some sort of ALIEN implant doohickey! You has been abducted by aliens!<br><br>Crap, I forgot to take my pills...<br><br>Trololo.
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!<br/>I've got a <strong>4 pin</strong> hall effect sensor. Will it work for this project?<br/>
dude, those resistors look older than me 8D nice 'ible though, i paid $40 for my sensor 8(
Your dog looks like my friend's brother xD
Then punch your friends brother, only dogs look cute like that.
Nice Dog. Not so good idea, there are better magnetometers out there, hall effect device is costlier then these.
That's not right. Telling us there is something better, then failing to tell us about it. Not constructive at alll.
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.
Do that. Put one in her shoe, or the sole of her shoe. That will really drive her nuts.
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?
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.
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. <br/><br/>Howard Johnson explains about this in his amazing book <a rel="nofollow" href="http://www.scribd.com/doc/34317/Spintronics-The-Secret-World-of-Magnets-2006-by-Howard-Johnson">Spintronics -The Secret world of Magnets.</a> There is information on page 31 on how they mapped the 3D fields.<br/><br/><pre>Have you ever wondered about:How magnets work?Why some elements are magnetic and others aren&apos;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.</pre>Howard Johnson, Spintronics<br/><br/>In other words, who will be first to create an instructable for a 3D magnetic field mapper?<br/><br/>Damn, I love this site.<br/>
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
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.
I love this. I don't really need one but I think I'm going to make one anyway.
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?<br/><br/>Such as this:<br/><a rel="nofollow" href="http://www.web-ee.com/Schematics/GaussMeter/GaussMeter.htm">http://www.web-ee.com/Schematics/GaussMeter/GaussMeter.htm</a><br/><br/>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.<br/><br/>Hall Effect Sensors can be found here for anyone interested:<br/><a rel="nofollow" href="http://www.lessemf.com/dcgauss.html">http://www.lessemf.com/dcgauss.html</a><br/>
thanks for posting that... I've been looking for a simple gauss meter :p
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
Something's missing in this picture. Oh, you forgot the magnet! Here it is:<br/><a rel="nofollow" href="http://www.hfml.ru.nl/froglev.html">http://www.hfml.ru.nl/froglev.html</a><br/>
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!
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!
Best Instructable to come through in a long time. 10 out of 10 without a doubt. Im pullin for you in the magnetics contest.
Excellent gadget. I think this goes up next to the magnetic stirrer for the magnetic challenge (so far)... Not sure which will place first though. That's up to the judges :P One thing that would make this even better would be steps of you putting one together from scratch. Still It's put together nicely (both the gadget and the instructable, especially your dog giving you a funny face)
I really like how you threw the 7805 into the schematic--I always hate having to look up which leads are power and ground, Tres cool, dude
That's cool!!! 10/10 for the nixies and 10/10 for the puppy!!!

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