Electroluminescent paint and multi-channel control circuit

tonight on Applied Science we're going to talk about electroluminescent spray paint that lets you put an electroluminescent display on any curved or even flexible surface and then also I'm going to show you a custom driver circuit that I designed that lets you get really smooth animations with your newly created electroluminescent device the electroluminescent paint is a commercial product called luma lure and when you buy it it's sold in this kit of different layers and what you do is spray these things down sequentially to make a display so the kit includes everything you need except for a way to deposit the paint and generally I've been using a little airbrush like this this one is called a neo it's about forty or fifty dollars on Amazon but you can also use this cheapo Harbor Freight one the difference is that this is sort of a siphon feed and this is sort of a gravity feed and the gravity feed cup is very small so if you're if you're doing very small objects it's helpful to have a really tiny airbrush so you don't waste paint this stuff is very expensive it's about 450 or 500 dollars for the set of paint and you know it sounds bad but if you're doing small displays this amount of paint will last you quite a bit I don't know what the coverage is exactly but I've been making all kinds of different test panels and you can easily spray something this big with the airbrush and it only uses you know a 50 if they're less of your bottle loom allure is targeted for the automotive industry and this company actually has quite a few good tutorial videos so I'm not going to rehash the whole thing but I am going to add what I've learned from it and also step through it quickly just so you can see the trick is if you want to make a pattern like this like if you actually want the light up area to be a pattern the easiest way to do that is to use a vinyl cutter and so the trick is that you load this vinyl into the cutter cut out the section that you want to light up and then use a transfer sticker to move the vinyl onto your substrate and then spray the copper paint which is the first step of this loom Alaura process through the vinyl cut thing so you end up with the copper pattern where you want the light to come out I've tried patterning every other part of this whole luma lore process and found that patterning the coppers by far the easiest way to control how the light comes out after the copper paint is fully dry what you want to use is a little thousand grit sandpaper to make sure there's no bumps sticking up I've noticed that the most common failure mode for this whole luma lure system is that there's a bump either a dust particle or a hair or a little bit of crust leftover from where you had a tape line where the paint kind of wicks up to the edge of the tape what this does is create a puncture point through the dielectric layer and shorts out your whole panel so you always want to be sure that your dust free and if you notice some kind of a bump you have to get some sandpaper in there and smooth it down and then repaint to make sure that there's no puncturing through the dielectric after everything is nice and smooth you can spray the dielectric on and this is more than just an insulator don't think that this is just that the sole purpose of this layer is just to keep these things electrically isolated the purpose is actually to create a tiny capacitor in there so the way electroluminescence works it's basically like a leaky capacitor and every time you charge and discharge the capacitor some of that energy goes into creating light so if your capacitor is no good to begin with because it doesn't have a high dielectric constant then you don't get very much light out in fact it doesn't really work at all so the dielectric constant of the stuff that's in this special paint is quite high its barium titanate is the powder that's in there and that's commonly used in all kinds of ceramic capacitors the next step is to spray a phosphor and there are about eight different colors available you can even mix and match them in the same panel which is pretty nice some are a lot brighter than others so this orange color is not particularly bright the green I think is one of the brightest ones they've got so you can kind of see the difference in light output here and then after the phosphor is dry we want to apply a clear conductive electrode to the top so that we can get light out of this whole stack up and the trick is there's this special material P dot P SS which is an acronym for polyethylene dioxide the afine polystyrene sulfonate I believe so it's a intimidating name but it's actually very easy to use material you just spray it on and let it dry and you've got a conductive clear electrode pretty nice and the electrical resistance is surprisingly low it's comparable to an IPO film but this is nice because you can spray it on with an airbrush and as it dries it becomes conductive and so you get this really cool effect when it's drying you can use a heat gun to kind of accelerate it it becomes conductive and sort of creates the display as its drying which is quite nice in order to attach your electrical connections to the panel that you just made luma recommends like jb weld or something i kind of prefer using this conductive tape made by 3m and so the the adhesive in this tape has little particles of medical of metal in there that pierce through the adhesive so you stick it down like this it makes a conductive bond to the surface and the adhesive is not particularly aggressive it's kind of like a post-it note I mean a little bit stronger than that but it's not crazy so you can pull the tape off and put it back on and it makes its it's a very low resistance connection it's totally fine for what we're doing you can also solder a wire onto the tape before you've applied it and then stick the tape on so that you don't expose your panel to anything high heat works great for these really thin substrates like the the printer transparencies too I've also noticed that I can touch the top layer I was going to say I've noticed I can touch the top layer without getting shocked but I actually kind of did get shocked that time a little bit that's actually the first time I've gotten shocked off of this system but anyway I can hang on to it like this and I'm not kidding shocked now I must have just hit just the wrong spot but in theory the clear conductive electrode is charged up over here so if you manage to touch both of these you'll definitely get a shock from it I've applied this pain to all kinds of different objects 3d printed objects this flexible printer transparency stuff even you know painted metal parts are okay even paper actually although the paper was kind of pushing it this was like glossy inkjet paper and it worked okay the the biggest problem I was having is that the masking tape was actually ripping the paper apart but it held the paint okay and the end result was not bad let's talk about the electrical side of this the luminol or kit comes with a couple of these little inverters which are pretty standard for driving e-l wire and al panels but these things have a couple of problems one is that they're only on or off like there's no dimming some of them will dim see that you can flash it and it's a little bit dimmer now but there's no programmatic control of this thing and the other problem is I'll put the microphone closed so that you can hear it they all whistle annoyingly so I wanted to come up with a better circuit that would allow dimming of the e L panel really rapid control for sequencing lots of channels no annoying whistling and as much other stuff as I can pack in so let me show you the circuit that I created to drive all these L devices okay here's the board let's start at the lower left here we've got a pair of LDOS a 3.3 and a 5 volt l do the 5 volts is required by the high-voltage switching chip which we'll talk about you could also supply the 5 volt with a boost converter or a buck converter or something else but I just went with LD is the control part of it like this whole area in here is basically an Adafruit trinket m0 in fact that's where I get the parts to build all this so the button the capacitors the 8e Sam D 21 microcontroller even the LEDs and the current limiting resistors are removed from the trinket which makes it kind of convenient because the chip has already programmed with the bootloader and the footprints are already in the board CAD program and everything so that's great and and also Adafruit is great and you can use some of the firmware that they've created which is very helpful also the way that the high voltage is created on this board is these pair of high voltage circuits that run in parallel and the one on the Left I've marked as optional oh btw because you don't really need both of them if you're not doing a high-power board you can actually just have one of these or if you are doing a mod to this board you could add more channels and get more a total power out of it the chip that runs this high voltage supply is an LT 3468 which is a a driver for a transformer and the transformer is actually this tiny little thing here it's actually the smallest transformer I've ever seen one of the other goals for creating this circuit was to make the board height as low as possible so the the USB connector in this big capacitor up here are the tallest components by far otherwise everything is under about two and a half millimeters so this LT 3468 is designed to run the transformer in flyback mode and generate a high voltage and the chip is pretty trick it actually has a voltage sensing circuit in there as well and it actually senses the secondary voltage by monitoring the inductive kickback on the primary which is pretty cool unfortunately it has a fixed voltage so I think it charges up to like 300 volts which is great but it's actually too much for this al driver which has a limit of about 200 or 250 I think and so what we do instead is actually use the MCU to monitor the high voltage and turn on and off the high voltage regulator very rapidly so that we kind of cycle sort of duty cycle the the high volt supply and this is actually a benefit because the firmware can control the supply voltage at will you can even adjust it mid program if you want which is great because then you can change the overall brightness of your al panels and if you have a really small al panel you can Jack the voltage way up to get high brightness and if you have a really large al panel you can turn the voltage down so that you don't exceed the maximum current ability of the circuit the circuit board is designed to accept one of two different high-voltage switching chips one of them is the HV 5/13 which is here and this has eight channels of high voltage output and the other chip is in HP 507 which has 64 channels high voltage output and they both work about the same it's basically just a shift register and so we shift in either one byte or eight bytes of data and the high voltage chip will basically just display that data in parallel on all the output pins I'll describe my circuit board build process briefly I use a little tiny ceramic heater on an insulator tile that I got from Amazon and I'll put links to all this stuff in the description and for boards that are small enough to fit on here this works great because I use the bench supply to power it and you can put a very precise amount of power through the heater to dispense the solder paste I prefer to use this pneumatic foot pedal controlled dispenser and so I've got a three cc syringe with a really tiny plastic nozzle here this is the smallest nozzle that McMaster sells I think it's a 27 gauge and it's t5 solder paste and I find that when I get just the right amount of coffee I can do a 400 micron pitch qfn the footprint with with this manually just hand holding it it usually comes out pretty well and then reflow fine sometimes I even use a little hot air from the top at the same time the hot plate is going just to sort of control the process and make sure it's nice and even generally this works really well I should also point out that this PCB was designed for my laser defined copper on plastic process so that all the traces are really fat and the spacings are a bit bigger than I would do if I knew I was pushing a conventional circuit board to sort of the you know packing limit basically the circuit will control il wire as well and so I made this glove that I wore around hackaday super con and it lasted all weekend which was better than I thought I actually stripped the plastic coating off the e l wire so there's there's still an inner plastic coating so they're still insulated but there's no colored outside on it so it's just like the core of the e l wire and there's 32 E L wires here using the 64 channels from this high voltage shift register chip and I'm using them in pairs and so the way that you works is that you know it's a capacitor basically and you want to deliver a square wave to each one of these capacitors and every time you flip polarity on the square wave you get a pulse of light out so the more rapidly you send a square wave to that signal to that vo wire you get more light out of it and so with the current speed that we can get I I can have about 64 grayscale control at 60 frames a second for each element which is pretty good don't get too excited though you can't drive like a 2 meter long il wire with one of these outputs potentially on the 8 channel driver chip you get more power because it's only 8 channels instead of 64 but with this one if you put a 2 meter piece of wire on here it won't light it up and I haven't figured out exactly what the limit is so it's more than 10 centimeters but it's less than 2 meters the power source for this thing is 6 double-a batteries and it lasts running this pattern about about 3 or 4 hours I think or so on those six doublea's so it's it's not a very power efficient circuit one 9-volt would not be enough to run this for very long at all and you can see I've got heat sinks on here because it's really not that efficient and those heat sinks are kind of more necessary than you might think depending how aggressive the lighting program is you can run a whole lot more power than you would otherwise like if you're very conscious about your lighting program you don't burn very much power but if you turned all the segments on to full brightness that would be way too much the circuit can handle about 3 watts constantly and it can peak up to maybe 7 or 8 watts but it can't dissipate that forever and so if you ran it at 7 or 8 watts for 10 or 20 or 30 seconds so it's probably melt something I also wrote a separate piece of firmware that transforms the outputs into a matrix driver so instead of using the 64 or 8 channels in pairs and then flipping each pair on and off to control each segment you can actually lay out all 32 in rows and columns and get this cool 32 by 32 matrix driving it though is pretty challenging because like I said every time you flip the polarity of any one of these electroluminescent capacitors you get a flash of light well this makes scanning through a matrix really difficult because you're constantly flipping something to address one pixel and then inherently you kind of flip all the ones that you don't want to touch so can conventionally in a in an LED or even an incandescent matrix you would put the state on the matrix and then hold it there for a while to let the light come out so that your switch time is very low compared to your hold times you get decent contrast out of it but that doesn't work with electroluminescent because there is no hold time you only get light out of the pixel when you're flipping its polarity which if you flip it more rapidly than you flip all the neighbors and you can't without it without a tri-state driver I can't see it any way of making this work however you might be surprised how well it does work and so I used pulsed off Riggins great octo ws twenty-eight eleven library to send some live video to the matrix so let me cue it up [Music] okay let's talk briefly about the firmware this is written in Arduino of course because it's an Adafruit trinket m0 I mean the chip really is a trinket m0 so everything when you plug this into the USB it's identified as a trinket m0 you can control the voltage programmatically which is here you can tell the thing whether you're using the HV 5 13 or the HP 507 here this max brightness is the number of grayscale levels that you'll have in your program and if you change this you'll get an automatic trade-off between framerate and number of grayscale levels so originally I guess I had 63 here and at 63 gray let the grayscale level so you get 134 Hertz refresh rate so at 128 you'll get about half that still pretty good it won't flicker as long as you're above about 75 Hertz there's a fair bit of manual register control in here because I really need detailed control over what these timers are doing so there's two main timers that each fire and interrupts to get this thing to run and the first one is a timer to set up here that runs an interrupt which sends data to the shift register so this is currently set up to run at about eight and a half kilohertz so eight and a half thousand times a second the chip fires an interrupt and sends it's basically its frame buffer to the shift register and that's pretty self-explanatory the second timers set up is a little bit weird it's actually set up as a one-shot and what this does is it fires periodically and if nothing retry Gers it then it doesn't run anymore and the point of this is that when this timer fires and interrupts it will check the high voltage on that capacitor and if it's too low it turns on the high voltage supply but what I want to happen is to have the high voltage be shut off if anything bad happens in the code so if the processor halts for whatever reason it can't just leave that high voltage control line in whatever state it was previously because it might have been on and if it leaves it on it will cause damage to the hardware so this is kind of a sort of thing so with the one-shot setup the the in or the timer times out and then if nothing happens like if the processor is halted for some reason it never runs the code to check if the high voltage is there and hence never turns it on that's the point of the one-shot the main loop is where you actually program the graphics for this thing and I have a whole bunch of commented out junk that basically you can have delays in the main loop because all the work is really being done by interrupts so you can you can delay the code in the main loop and set the pixel values to whatever you want the next step in developing this firmware would be adding like a graphics library or adapting a de fruits here's the interrupt handler that sends the data to the shift register and this runs at about eight and a half kilohertz and I measured it for a twenty second duration so that's like seventeen percent of the CPU time is spent in this interrupt which is I think it's pretty reasonable for this application and the trick here is that every time you toggle a pair of lines going to an e l panel or wire you get a flash of light out of it so I have this loop that basically checks to see if the pixel value is or if the current sort of iteration through all the possible pixel values is less than the value that you want it to be and if it is then it toggles those two lines and remember a toggle means give me a flash of light so fade step increments one by one as this loop runs and eventually it will get higher than pixel values whichever I mean let's say your pixel value is set to 50% halfway through this loop fade step will get higher than the pixel value and then it won't toggle that line anymore so this thing basically steps through all the possible brightness combinations and will light up only the pixels that are set to be higher than that cut point here's the interrupt handler that runs the high voltage setup and it's important that we disable interrupts for this one because we really can't have any interruptions during this time here because it is pretty time-sensitive there's a quirk with that high voltage chip that I'm using you can't pulse it too rapidly so there's a minimum load time which is why the loop is set up this way I'm not gonna really get into the hardcore details but of course if you have questions about this you know contact me on Twitter or put them in or even better put them in the in the comments and then everyone can learn from it okay see you next time bye

Channel: Applied Science

Views: 468,596

Keywords: Applied Science, krasnow, lumilor, electroluminescent, paint, glow, glowing, foldable, flexible, display, matrix, high voltage, EL, wire

Id: eUUupR-ongs

Length: 21min 47sec (1307 seconds)

Published: Wed Nov 21 2018