January 2011 Archives

Originally we were tasked with automating a DMX board, and syncing some of its functions with audio.  There are literally zillions of ways of doing this, especially if your pockets are deep.  One option was to use a Gilderfluke or Alcorn-Mcbride product-- a programmable show controller, and interfacing it to an expensive lightboard like ETC or Horizon.  However, we had the hardware lying around to change a mac mini, into a full show control system with lightboard function and gui. This is nothing groundbreaking, but it's still fun.  Most of all, we didn't have to source a lightboard.

The i/o interface was the Phidgets 0/16/16.  This was convenient since it was usb based and provided a total of 16 inputs and 16 outputs, all opto-isolated.

The DMX interface was the Entec DMX usb pro, utilizing a purchased copy of dmxusbpro by Olaf Matthes. 

Everything was then tied together in the max/msp programming environment.  The "under the hood" was covered up with a nice interface for the general user.  The prize-winning max object on this one was "col."  It essentially allows a user to program cues via text files (which is nice if you are programming 12 cues at a time to a fixture), without knowing a thing about max/msp.

In the end, for a little under $1000 we have a mini show controller with these features:

-control 1 DMX universe, 512 channels, via GUI.

-trigger events on a schedule for complete automation

-16 digital triggers

-16 digital outputs

-audio and event playback via trigger

-programmable and expandable cues/events

-diagnostic panel (power, status, connection, etc)

-nifty interface

It was mostly a rush job, and a lot of sweat was poured when nothing worked, at all.  The manufacturer's manual for one of our DMX devices, was written so that a lot of guestamation had to be used.  A contractor had also done some funny stuff with dmx to microplex adapters, ensuring that failure was imminent. In the end it was a success.  if i had more time, i would have added a log feature and terminal access.  The "exciting" bit is that the entire system can be tweaked to interface with shell scripts.   

A few years ago I was at a pub, celebrating a peers birthday, when a friend in education asked about using electronics to teach children sound--specifically how bats echolocate.  I was stunned, and probably turned alcohol into enthusiasm all night long.

Well, the joke was on me, because then I really had to build them.  The actual wiring and programming of the devices are pretty much textbook.  I was already familiar with the Basic Stamp and Ping sensor.  So the hard part was really making something novel, attractive and durable for children; it also had to meet the teacher's criteria.  A lot of this came down to the casing, and small tweaks in programming.

So a couple of prototypes were made.  One version was very ghostbusters, with a column of LED's that went from green, to yellow to red (corresponding to distance over 12 feet), all housed in a shiny handheld aluminum casing.  In the long run this wouldn't work; the proto box wasn't meant for something "real."  After that i tried some off the shelf items from tap plastics, but nothing fit the durability and pricepoint which had been spec'd.  Finally, i found a bunch of acrylic q-tip containers with lids at the container store, and began to modify them under the drill press.  One, or two of these boxes, may have died by my hands.

When the first unit was ready, there were two forms of output: 1) the 7 segmented display indicating the distance (up to 7 feet)  2) the audio, which was an analog of the digital output from the ping sensor.    

However, the teachers thought the theremin quality of the device was confusing, so instead it simply beeps in correspondence to the major scale, getting higher as the distance approaches 0, in steps of 1 foot.  If you're wondering why it only reads to 7' on the display when a prototype went to 12', it's because i didn't pay attention to the stamp's max output current per pin rating.  We'll leave it at that.   

Anyhow, the first one was made, by hand, all wire-wrapped, with zero documentation.  This would prove to be a fatal lesson as I would eventually need to make a total of 8 devices.  However, it's pretty cool that san francisco school children have been jacking bat-ear headphones into these, closing their eyes, and navigating a custom syllabus for over 2 years.

Of course, most of what really happened was our "cart of toys"-- a collection of relays, solenoids, motors, microcontrollers, sensors etc.  We gave our presentations, answered questions, but most of all, let them play.  It's really motivating to see how quickly children can comprehend a subject so often bathed in mystery and abstraction.