Sunday, March 17, 2013

Hall effect sensor circuit prototype

Amendment to this first sentence: I'm not going to explain exactly what we're working on till our primary prototype is done.  The astute reader will be able to connect the dots. However, I'd like to maintain a level of suspense about the exact nature of this project.  A full overview will have to wait for our Kickstarter campaign.
Perhaps this post places the cart before the horse (talking about a project before I’ve explained scope and goals), but I feel a bit of momentum and want to blog about the past three days.  +Jason Hoff , was out for a visit and we had an opportunity to monkey with a couple of projects.  One is from the past, a (2 degree-of-freedom) tilting table drawing machine, whose design evokes the words “Eiffel Tower” (from all who gaze upon it’s visage) .  The other, is an upcoming project that Jason and I are partnering on, a dynamic labyrinth/maze game/kinetic sculpture.  Both utilize Arduino micro-controllers for sensing and control of the kinetic structures of these “sculptures”.  Needless to say we spent a bit of time fooling around with electronics and software.

Using hall effect latches we were able to prototype a 2 x 2 sensor array that can detect the presence of small rare earth magnets within about 1/4” of the sensors.  To represent the presence of a south pole field we also wired up some LEDs in a 2x2 grid (circuit diagram to be provided).  The IO for the sensor circuit and LEDs were all run into an Arduino, where we handled the signal processing and control.

(video of sensor circuit working)

We learned a number of things from this little project: first, Jason can still do simple electronic (after a 15 year hiatus), second, using a Hall Effect latch is not the appropriate choice for this application.  The problem springs from the nature of the latches we were using, being a “latch” means the device retains it’s state information even after the magnetic field is moved from its proximity .  A word to the wise, don’t send a computer scientist/artist (me) to buy electronics parts (you’ll usually end up with almost, but not quite what you need).  This property required us to “clear” the latches by driving current into their sensor leads (no specs given whether this is a good idea or not).  After my trusty EE (Jason) researched and poured over some spec sheets he determined that we should be using omni-polar Hall effect switches.  These switches don’t require clearing (thus eliminating the clearing circuit) from the production model of this circuit.

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