Electroluminescent paint and multi-channel control circuit--make money online

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

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