Sunday, March 31, 2013

Lost in translation...

A delightful email from the folks sending me some linear motion bearings.  I have parenthetically responded to add a little levity to this already amusing epistle:

We are excited to inform you that our Mr. Pigeon has started off and covered 25% of its journey. As stated in our auction, the shipment will take about 10-25 days during the delivery. Please be patient and wait for the arrival of your lovely item. 
(Actually, there are 10 of them, and I have little other choice than patiently waiting.  I suppose I could jump up and down, but what good will that do me?  Also, you might consider how PETA will react to your forcing a pigeon to carry nearly a dozen stainless steel bearings. On second thought, the western world is concerned about how China treats it's own people. So I suppose birds that have been pressed into service as beasts of burden aren't really on PETA's radar.)

(Notice: Since the air cargo capacity of China Post has been impacted due to a high volume of items, there might be a delayed shipment of some items.  So if unfortunately you haven't received the item within the expected time, please be patient and wait for some more days. Thanks for your kind understanding.)
(I'm a little suspicious that the air cargo capacity of the Chinese postal service is impacting the delivery date of my bearings.  If the air cargo capacity actually is the cause, I'd advise not using pigeon delivery.  My guess is you forgot to fill my order or mail it in a timely fashion.)

Should you have any queries, please feel free to contact us via 'eBay Message'. We will try our best to assist you to resolve the challenges facing ASAP. 
(Though this might provide for entertainment, while I wait, I doubt anything can be gained from further communication.  If my bearings never arrive then I shall be contacting eBay for a refund.)

Once again, thank you for giving us the opportunity to share with you our products. We strongly believe that quality, blended with excellent service, is the foundation for successful business. 
(Telling me my stuff will arrive later than I had expected, when I have no expectations is not what I'd call "excellent service".  In fact I doubt the bearings will be very high quality, I purchased them because they were dirt cheap and everyone else wanted 10 times as much for the same damn thing.)

Yours Faithfully Seller, 

Saturday, March 30, 2013

If at first you don't succeed...
Ask for help, then buy an off the shelf solution.

Finally got the bigger solenoid working,  just ended up having to pull all of the current limiting resistors.  By work I mean I made the nail actually move, not with much force or very far, more worryingly the power supply was making an ominous hum the whole time it was plugged in.  For the moment I'm done trying to build my own solution, it would take way too long and far too much wire to wrap 56 of the damn things (for the prototype).  Ordered 10 of these pesky things.  Many thanks to +Michael Seedman for talking to me about solenoids and sending me this and other photos.

(surprisingly made in the USA) 

Friday, March 29, 2013

Failure to transduce...

I've been poking around, looking for solenoids to fit into the block lifting mechanism I'm designing. Nothing I've found looks terribly compelling, inexpensive or the right size. So I tried to make one (it's a simple concept, wrap a wire around a non-conductive tube (a bunch of times), stick a ferrous cylinder inside the tube.  Then apply a current to the wire and (hopefully) a directional magnetic field is generated.  I've wrapped 2 different solenoids and run current from a 12V 3A supply through them and no dice, no ferrous material moving.  Grrr...  Any ideas?

 (one with 2 layers of wrapping another with 4)

(the circuit I'm using)

Wednesday, March 27, 2013

More Nerdy PCB Stuff

So, if you are nerdy (like me), and you're curious about making your own PCB's for your projects, you might be interested in our experience designing the Hall Effect Unit PCB.

There's tons of software out there for PCB development, the consensus among most hobbyists seems to be either Eagle CAD or KiCAD.  My own preference ended up being KiCAD, for one it's free (gpl) and free ($$), also it runs under several Linux distros, and after using it a bit, I liked the component library editor better than Eagle's (critical, since unless you have a large commercial library at your disposal, you are going to be making a lot of your own component models, which is annoying but pretty easy with a good editor).   There are plenty of tutorials available for both KiCAD and Eagle, I won't bore you with details, I found this one for KiCAD to be pretty useful.

The whole process, from an idea, to completion of all CAD work took me about 8 hours (that includes installing KiCAD and Eagle and then deciding on KiCAD, messing around with a tutorial, creating 2 library components, and then creating the schematic and board).  It's really pretty doable / even easy, or at least I hope it was, this was my first PCB design, so we'll see if all the components actually fit on the thing when we build one.

The final output from the CAD design flow is a set of gerber data files (one per board layer) that describe where you want copper or not when the board is etched, plus a drill file for the vias.  This is all that's really needed to manufacture one of these boards.  For a two layer board its very straightforward, but sorta cool looking, see screenshots from my gerber viewer for the Hall Effect board ...

Top Layer

Drill File

Bottom Layer

Amateur PCB Night

We just finished the unit circuit board for the position sensing network that will be used with the "project" which will remain unnamed until Ian's blood pressure subsides enough for additional Google searches on the words "labyrinth" and "maze" to proceed.  The board is pretty simple, a couple 2.54mm pin header strip connectors, and two open drain omni-polar (switch output drives low for both north and south pole fields equally) hall effect switch IC's.  Overall, very similar to the circuit we bread-boarded in an earlier post with the exception of the latches which are replaced with omni-polar switches in the final circuit.  The switches should be much smoother in actual operation, they are roughly twice as sensitive as the latches (magnets do not need to be placed as close to the sensors), and of course we were able to dispense with the circuitry needed to clear the latches in the absence of a field (the switches stop driving as soon as the presence of the magnet field is removed).

KiCAD Board Layout
KiCAD Board Schematic

The idea is to string together a bunch of these 28 sq mm PCBs in a grid shaped sensor array underneath the game board (the final project will utilize 256+ PCBs).  Each moveable piece on the board / sculpture will be embedded with a small rare earth magnet which will induce a magnet field to trigger the sensors.  Ian's friend Michael came up with the (pretty cool) idea to connect all the open drain outputs in a particular row or column in a wired-OR configuration.  If any unit circuit in a row (or column) detects the presence of a magnetic field it pulls down the wired-OR output for that collection of sensors.  This reduces the number of GPIO's required to read a position from the grid, and using an Arduino to read each row and column output, it's simple to detect which squares in the 256 sensor grid are occupied by reading only 32 inputs.

Monday, March 25, 2013


No, it's not national talk like a pirate day, I'm just pissed that the word labyrinth has been co-opted by fucking religion and spiritualism.  On Google's top 10 links for a search on the word 'labyrinth' you'll find "The Labyrinth: Walking your spiritual path".  Googling the words 'active' and 'labyrinth' leads to even more superstition and religious horse shit.  Is it really that hard to leave be the concept of a horrible maze where a freakish half-man/half-bull slaughters sacrificial victims on an anual basis (demanded of the Athenians by Minos, King of Crete)?  Is nothing sacred?  So much for 'active labyrinth' as a name for this project...  It'll have to be Mighty Morphin Maze or the Moving Maze.

Sunday, March 24, 2013

Block Lifting Mechanism

Been working on a design for a mechanism that will lift and lower blocks for the active labyrinth project.  Have some linear motion bearings on order from China.  The rack and pinion are not the correct size.

Tuesday, March 19, 2013

Pink Floyd laser light show... No, no, no...

The tilting table (that draws with a ball rolled in graphite or ink) was a project for my kinetic sculpture & embedded systems course about a year ago.  Most folks called it the "Eiffel Tower" which, I admit, partially inspired the piece.  It was popular among my classmates and probably a bane to at least one of my professors (who spent a large amount of time, at least 10 hours, supervising me with the art department's laser cutter).  Anyway, the project never really got the time it deserved, the control software was never great and the servos have always been a bit jerky.  +Jason Hoff  and I set it back up and started working again on the electronics and software, we didn't make as much progress as either of us had hoped.  The servos, even when slowed down, were still quite jerky and the new control software I've been working on didn't really do the trick of imparting better control over the drawing ball.  In the long run if I want this thing making drawings and art I'm thinking I'll need stepper motors and a far better set of control algorithms.

Here are some shots of the table with the lights off, a small shutter and long exposure times.

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.