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• High voltage DC?! Seems safe...

  fool • 09/04/2017 at 00:19 • 0 comments

  The next step of this project was to move beyond using an existing "self-oscillating" supply and instead try to design one of our own (that didn't spike without a load, and that didn't make an annoying 1-2KHz buzzing noise).  

  We decided that it would be nice if this supply ran off of 5V, so the first step was attempting to design a DC-DC boost converter that transformed 5V into ~150.

  To do this we first tried using the LT8304 for the control circuit, and then tried the AZ34063UMTR.

  
  Both of these had problems with efficiency though, and ultimately, we decided to return to the problem of designing a better DC-DC converter at a later time.  For testing, we took a standard wall wart, and rewound the transformer so that it would output 170V DC. 
  

  This is not a particularly safe thing to do (and would almost certainly violate some safety guideline regardless of where you attempted to distribute such a thing), but for testing it's been really handy :).
  

• A concrete simple instance!

  fool • 09/02/2017 at 20:18 • 0 comments

  Here is a better, and brighter way to power things with an external supply:
  

  And here it is in action, powering a large panel and a surface painted with electro-luminescent paint (developed by a company called LumiLor).
  

• DO NOT DO THIS!

  fool • 09/02/2017 at 18:58 • 0 comments

  Here we're going  to document our first experiment with connecting an external supply.  

  It worked, but it is a BAD idea (for a few reasons that we will detail here). Please learn from our foolish explorations - don't electrocute anyone!

  Ok, so what are we looking at here.  We are looking at a regular american power plug, that fits into a supply that provides ~120V (RMS) at 60Hz.  We attached a resistor (and didn't include a TVS diode because there is one on the board and because the voltage in the wall shouldn't exceed 170V as long as there isn't a spike).  We flip the supply switches on the board, and connect this as an external supply. 
  

  Okaaaay, so why is this a BAD idea?

  The main issue is that because we are driving the panel directly from the wall, if you touch the panel then there is a potential to create a ground loop through your body, because there is no galvanic isolation between the supply and your feet. 
  

  BAD BAD BAD!
  

  This is particularly worrisome because the board is exposed, and so it's easy to touch an exposed lead, and because the panel in question isn't sealed/laminated, and so can shock you when you touch the edges of it (as has happened to us, particularly when touched with sweaty/moist hands).  

  If you want to draw power from the wall, it is much better practice to pass the signal through an isolating transformer.

  That said, EL materials really glow much more effectively when driven at a higher frequency than 60Hz, and so it is better to use a more specialized supply, as we will describe in later posts! 
  

  -----------------

  There are, however, some redeeming things about this experiment, as we illustrate in the image below:
  

• Choosing a TVS diode!

  fool • 09/02/2017 at 18:54 • 0 comments

  Fill fill out more information here later!
  

• A simple solution!

  fool • 08/31/2017 at 03:48 • 0 comments

  As mentioned previously, the limitation of the whoa board is that we are not allowed to put more than 3A and 150V (300 peak to peak) through it. 

  Accordingly, a simple solution which can make it compatible with any power supply is simple to limit the current and voltage going into the board.  

  NOTE: THIS APPROACH REQUIRES THAT A NON-TRIVIAL AMOUNT OF POWER BE DISSIPATED IN THE EXTERNAL COMPONENTS.  PLEASE REFRAIN FROM STARTING ELECTRICAL FIRES.
  

  This means that they have to be chosen appropriately to withstand the situation where the whoa board doesn't provide a load (as happens for part of the time during every touch sensing cycle).  

  This is important because the self oscillating power supply designs (like the ones in the videos in the previous post, and generally most commercially available EL supplies) increase in frequency and voltage as the load decreases.  In fact, some supplies cannot be turned on without load because they will fry themselves.

  Annnyway, in the interest of documentation, let's work out the math of how to appropriately choose these resistors and diodes here.  

  Let's suppose at it's max, the external supply outputs 400V peak to peak, and to be conservative, let's limit the max current to 2A. 
  

  In order to limit this current, we need 100 Oms of resistance.  The path that the current flows through is already ~50 Om, so we need another ~50 externally.  For the sake of symmetry (and to distribute the power dissipation) it's probably better to instead include two ~25 Om resistors, as drawn in the above schematic.  

  Because EL loads are capacitive, they have a much higher peak current than average current, which makes it difficult to compute a power rating for the resistors you choose.  For most applications, a 1W resistor will probably be fine, but if you aren't sure, there's no beating experiment.  If it starts getting uncomfortably hot, increase the power rating :).  
  

  In the next log, we'll talk about power dissipation in the above TVS diode! 
  

• EL Power Supply Resources

  fool • 08/29/2017 at 16:16 • 0 comments

  Online resources for designing a high frequency, high voltage power supply that is happy driving a capacitative load are not particularly easy to find. 
  

  The closest project to ours which we could find was this one:  http://www.kobakant.at/DIY/?p=4101, http://www.kobakant.at/DIY/?p=2992  (and for those that haven't seen it, the rest of the Kobakant site is also worth exploring!)

  
  Jeri Elsworth also made a few videos about EL materials (above is her exploration of a self-oscillating EL supply). 
  

  And here is a video that tears down another (self-oscillating) commodity EL supply:
  

• A technical challenge!

  fool • 08/27/2017 at 04:30 • 0 comments

  So far we've defined an assistive technology product for integrating interactive lighting into spaces for the mobility impaired. Now we can start hacking to figure out what needs to be done in order to get this implemented!
  

  The main challenge here is that the on-board power supply on the Whoa Board is based on the MIC4833.
  

  The way that it works is by first generating a 110 volt DC signal (from 5v, using a high frequency boost circuit), and then generating an alternating current out of that by passing the DC signal through two alternating half bridges (which we have set to oscillate around 700Hz).

  We chose because it was quiet (ours is one of the only EL drivers that doesn't make a 1-2KHz buzzing noise), but is limited in it's power output, and cannot power EL elements on an architectural scale.  Fortunately, we manufactured the whoa board with the ability to accept an external power supply!  

  The way it works is as follows:  At the core of the Whoa Board sits a fast high voltage switch (that we control using a bit-banged serial protocol). In order for the switch to switch, it needs a "min" and "max" voltage reference as an input to it's level shifters.  

  We obtain this reference for an external supply by disconnecting the onboard supply (to protect it) and then by passing it through the coupling circuit at the top of this post.

  Note: If you forget to flip the dip switches and connect and external supply, you will probably fry the onboard EL drive circuit (and maybe something else as well).  

  The ground marked optional is something that we've found helps protect the board, but is not currently integrated.  We are happy to provide instructions on how to add this for anyone interested.  

  Finally, note that the touch sensing doesn't work on "first edition" boards with the external supply without a bit of rework.  Again, if you have a board and want more insight, happy to answer questions. 

  The onboard switch also has a few additional constraints which end up presenting challenges.  First off, it is rated for a peak current of 3A, which is worth bearing in mind because EL loads are capacitative.  Secondly, it cannot safely bear a peak reference voltage of more than 150V.  
  

  ---

  Now that we have this circuit, we are ready to define our hack!

  Namely, we set out to create a power supply capable of driving a capacitative load at ~100V and ~1KHz, that can safely output ~5 watts, and is also compatible with the above constraints!

• Y Du Dis?

  fool • 08/26/2017 at 21:38 • 0 comments

  Existing Solutions

  There are a number of existing solutions for adding night time lighting to living environments.  There are of course light switches and lamps on your bedside table. There are the ever present night lights.  There is the infamous clapper (which is sure to startle your partner).  More recently there has been an influx of motion sensitive LED lights, as well as time sensitive lights that only activate at night.  

  There are also a number of app based wireless lighting controllers that are emerging.  

  Why Moon-Lites?

  We have spent the past two years developing a technology for prototyping applications for making electro-luminscent materials touch activated.

  This board makes it possible for MOON-LITEs to offer several novel features over what is otherwise currently available.  

  • Touch them anywhere to turn up the brightness

  The Whoa Board at the core of each MOON-LITE is the new technology which makes this possible!

  • A low brightness motion activated mode

  MOON-LITEs are wirelessly networked and are configured to turn on in a very low brightness state when they detect motion.  This makes them easy to find, while making it less likely that they'll wake someone up if they roll over in bed, or if their cat comes into the room in the middle of the night. 

  • They can be turned off.

  The Light-Lite integrates into any light switch cover, making it easy to tell your MOON-LITEs that you are done using them and you are ready for them to turn off, something not currently possible with more traditional motion activated systems.

  • Easy to integrate.  

  EL materials come in paint, panels (like sheet of paper or strips of tape), or wires.  You don't need to call a contractor to install a complicated lighting system only to find that it doesn't work for you.  Just stick some tape on your wall.  If it doesn't make sense, move it around.  There is a low barrier for experimentation to help people arrive at the best solution for them.  Stick some tape on the edge of your furniture to make it easier to avoid at night.  

  • Seamless operation.

  MOON-LITEs are simply evolutions of existing household objects.  There is no new interface to learn, you don't need to find a phone.  Simply continue moving around your space as you did before, but with more confidence!

• A user story!

  fool • 08/26/2017 at 19:57 • 3 comments

  After doing these interviews, we came up with an archetypal human that we'd like to help with the technology we have been developing.  In the following post, we detail a scenario where we imagine interactive lighting could help a mobility impaired person live a fuller life.
  

  
  

  For Rose, we created three modules which work in tandem to make her life safer in seamless way, by augmenting her existing interactions.

  
  

  Consider how these three MOON-LITEs interact in the following scenario!

  
  

  Rose wakes up hungry in the middle of the night.

  
  

  The MOON-LITEs detect her motion and enter a low brightness mode, highlighting obstacles in the room, and making it easy for her to get a bit of extra guidance if she needs it.

  
  

  When she grabs on to any MOON-LITE, all other lites (as well as other optional LED lighting) enter a high brightness mode to give Rose a bit of extra assistance as she moves around.

  On her way back to bed, she can tap on the outside of the light-switch to deactivate the MOON-LITEs, something not usually possible with a motion activated system or turn on the room lights if she needs to find a book on her shelf.  

  If she forgets to tap the Light-Lite, the MOON-LITEs will all turn off automatically if they don't detect motion for a few minutes.

• A physical trail marker!

  fool • 08/15/2017 at 00:09 • 0 comments

  One suggestion that received lots of enthusiasm was working with physical therapists to create a rehabilitation game.  

  We designed a very crude visualization, however there is lots of room to flush out and improve on our idea! 
  

  
  The sense that we got though is that it would be helpful to create an interactive "mat" that physical therapists could easily program to create exercises for people recovering from strokes!
  

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