Introduction: Illuminated Touchscreen Poster Frame With Subliminal Message!
Well, as often happens in my brain, complexity increased at a geometric rate and I came up with this mother-of-all-poster frames. It is illuminated using 28 super-bright white LEDs, mounted along both lengths of the frame. It is activated using a capacitive touch sensor. It uses surface mount technology. And best of all, you can activate a subliminal message from the Serenity movie that *could* cause you to flip out and beat everyone in the room to a pulp.
Interested? It's your lucky day! I will teach you how to make one. You can use any poster you like, but this Instructable is based heavily on the "Miranda" poster from the set.
EDIT: Please vote for me in the Epilog Contest! Why? Because if I win, I will be donating the laser cutter to the fledgling Maker group starting up in my city. It would go a long way towards our goal of a Maker/Hacker space in Waterloo!
Step 1: Materials and Tools
I tried to keep this project as Green as possible. First off, by illuminating the poster using LEDs instead of fluorescent light, I'm avoiding the use of all the toxic chemicals that go into making fluorescent tubes and ballasts. LEDs also consume less power. All of the components purchased at Digikey and Mouser are ROHS-compliant. I used lead-free solder. Lastly, the polycarbonate plastic sheets I used were scraps purchased from a second hand store - much cheaper!
From the Hardware Store:
- Three sheets of acrylic, Lexan or polycarbonate sheet, at least 2.5mm thick. Two should be the same dimensions as the poster, and one should be 2 inches larger in each dimension.
- aluminum duct tape (the stuff that is actually made of aluminum) - make sure it's shiny on the adhesive side, too!
- regular grey duct tape
- electrician's tape (any colour - I used yellow to match the yellow of the poster)
- masking tape
- four machine screws with matching washers and nuts
- epoxy or other glue that adheres to plastic and dries optically transparent
From Digikey or eBay:
- 34 3mm or 5mm bright white LEDs
- 14 3mm or 5mm bright red LEDs
- 2 QT100A touch sensor ICs (427-1135-1-ND)
- 1 D-type flip flop IC (296-9851-1-ND)
- 1 5V regulator IC (497-1171-1-ND)
- 2 N-channel logic-level MOSFETs (ZXMN6A07ZCT-ND)
- 1 inverting buffer (296-8483-1-ND)
- 8 68 ohm resistors (regular 1/4W through-hole type)
- 3 150 ohm resistors (regular 1/4W through-hole type)
- 4 51 ohm resistors (regular 1/4W through-hole type)
- 2 100k surface mount resistors (RHM100KECT-ND)
- 1 1k surface mount resistor (RHM1KECT-ND)
- 4 10 ohm surface mount resistors (RHM10ECT-ND)
- 2 10nF surface mount capacitors (311-1173-1-ND) ******** depends on sensor!
- 2 100nF surface mount capacitors (311-1179-1-ND)
- 2 10uF tantalum surface mount capacitors (718-1044-1-ND)
- 1 "SchmartBoard" Discrete #2 protoboard (872-202-0035-01) (or you can make your own PCB)
- 1 12V AC/DC adapter
- 1 socket to match the plug on the adapter
- assorted wire (I suggest 26 AWG stranded wire with Teflon insulation)
- solder flux
- Kapton tape (or masking tape in a pinch)
- A table saw or band saw (for cutting plastic panels)
- A drill press
- An oscillating palm sander
- A belt sander
- A Dremel tool with engraving bit, or an engraver (or better still, a laser engraver!)
- a metric ruler
- a nice precision soldering iron
- other assorted hand tools, as needed
Step 2: Prepare the Plastic Sheets
There will be a total of three layers of plastic that make up the frame. The top layer is completely clear, and mostly decorative. It is larger than the poster itself to give a modern look. It also prevents the poster from flopping out onto the floor.
The middle layer is where the "subliminal message" is hidden. It features a graphic etched onto the plastic, so that when the plastic is edge-lit the graphic is illuminated and shines through the poster. When the message is unlit, it becomes invisible.
The bottom layer is the "backlight." One of the faces on this layer is completely sanded to diffuse light, while the other face is covered in a reflective material. It has 14 LEDs mounted on each side, whose light disperses and illuminates the entire panel.
The top layer should be cut so that there is about an inch of plastic border all the way around the poster's edge. The Serenity poster is 17x22," so the top layer is 19x24." The best way to cut the plastic is by cutting it on a table saw. I don't have a table saw, so I roughly cut the plastic with a Dremel tool first, then cleaned up the edge with my band saw. You could also have the plastic cut at the store, if they have the facilities to do so. I don't recommend scoring and snapping off the plastic - it always seems to go terribly wrong (at least it does for me!)
The middle and bottom layers are the same dimensions. They should be cut slightly smaller than the poster's edge, about 1/4" on all sides - about 16.5" by 21.5." This is done so that the LEDs around the sides can be hidden.
Step 3: Sand and Cut the Bottom Sheet
I studied up on how LCD backlights work, and tried to craft a reasonable facsimile. The basic idea is that light enters from the sides and bounces around inside the plastic sheet, like in a waveguide. When it hits a disturbance in the face of the waveguide (the sanded side) the light scatters, some out of the plastic and some back in. The light that stays inside the plastic is reflected back out by the reflective tape on the back. Light that manages to reach the edge of the plastic is also reflected back into the plastic. Hopefully, most of the light produced by the LEDs eventually leaves the sanded face of the plastic sheet in a somewhat diffused manner.
This is the fun part! If the plastic is covered with a protective plastic film, peel it off on ONE SIDE. Now, grab your random orbital sander and go to town on it! Sand the entire face of the plastic so that it has an even "frosted" appearance. A powered sander makes this job pretty fast, and produces a nice even finish. You can hand-sand it, but it won't turn out as nice.
Next you must mark out where the LEDs will go. Lay a piece of masking tape right to the edge of the plastic on both of the long edges. Put a mark one inch from the end of the plastic. Then, place a mark every 1.5" after that. You should end up with 14 marks on each side.
Using a metric ruler, place a mark 2.5mm from either side of each of the 14 marks. Each pair of marks (spaced 5mm apart) indicates the position of a 5mm diameter LED. If you're using 3mm LEDs, space the marks 1.5mm from the center.
Now, at each of the center marks, place a fourth mark 5.5mm from the edge. This crosshair indicates the drill hole for each LED.
You can drill the plastic sheet with a hand drill, but a drill press works much better. Using a 13/64" drill bit (or better yet, a 5mm metric drill bit), drill a hole at each of the 28 cross-hairs (14 on each side). Work slowly and don't force the drill, or you may break the plastic. Acrylic is more prone to breaking than polycarb or Lexan.
Finally, with a band saw or hand-held saw, cut on the inside of each 2.5mm mark to the drill hole. You should have a notch that is 5mm wide, and conveniently LED-shaped. Take you time and cut carefully - the less you have to fill in later with glue, the better!
With 28 neat LED-shaped notches cut, you may remove the masking tape.
Step 4: Etch and Cut the Middle Sheet
This part takes a while. I chose a pretty complex pattern, you may want to use something simpler. Perhaps a simpler graphic, or a quotation from the movie. It's up to you!
I grabbed this fantastic image from the 'net. A Firefly fan, presumably as devoted as I am but possessing an entirely different set of skills, created a desktop image based on a scene from the Serenity movie. In the movie there is a short commercial that contains a subliminal message. When one of the characters (River Tam) sees the commercial, some government-embedded training is activated and she goes on a rampage inside an unsuspecting tavern. Unfortunately I was unable to find a link to this picture on Flickr; please let me know if you find the original!
I used the now-ubiquitous method of edge-lighting an image engraved into plastic, so that the engraved image illuminates but the rest of the plastic remains dark. The image shines through the poster when lit, but is nearly invisible when unlit.
I started by making the image I grabbed black and white, since engraving is a two-bit process - engraved, or not engraved! I also removed all of the background, leaving just the text, the octopus and the two girls. Printed on a sheet of 8.5x11 paper, it fit perfectly in the mostly empty yellow space of the poster.
If there is any, remove the film from the side that will be etched. Tape the image on one side of the plastic, being careful to align it with the empty yellow space on the poster. The printed side of the image should be against the plastic, so that it is visible when you look through the plastic. The image will be etched on the face that will eventually sit directly against the poster, for the sharpest resolution.
Now, with an engraver or Dremel tool, begin engraving the entire image into the surface of the plastic. You'll probably work with only one eye open for the whole thing, to get the right perspective. Work carefully and try to get nice smooth edges. Choose the right bit for the complexity of the particular section you're working on. Lastly, don't expect to finish everything all in one afternoon - your arm will be screaming for mercy! Break it up into a few smaller sessions.
This is where having a laser cutter would be nice. Simply set it to engrave mode, convert the graphic into compatible CAD data, and relax while it does the work. Have I mentioned that I really want a laser cutter?
Once the engraving is done, you will need to cut notches the same way as you did for the bottom sheet. Fortunately, you won't need to cut as many - 14 will do, 7 for each side.
Step 5: Grind the LEDs
Since I used 2.5mm thick polycarbonate sheets, I had to grind the LEDs flat on both sides for a flush fit.
I used a belt sander to do this (attached to my band saw), and it went really fast. Simply sand down the sides of the LEDs until they resemble tiny tombstones. Don't take off too much plastic though, just enough so that the LED is the same thickness as the plastic.
If you're using 3mm LEDs you may not have to remove any material at all. Similarly, if you used thicker plastic then you won't have to sand the LEDs as thin.
Do 28 white LEDs (did I mention how handy a belt sander is?) and 14 red LEDs (it's really handy!)
Step 6: Glue in the LEDs
For optimal light transfer, the LEDs must be glued in the notches. Any glue that dries optically clear will do - Krazy Glue, many epoxies, or acrylic solvent cement.
To start, lay a piece of clear scotch tape or packing tape on one side of the sheet, along the edges with LED notches.
Inside of each notch, stick in an LED so that it is pushed as tightly into the notch as possible. Be sure to observe polarity - each LED should be placed the same. Put a glob of glue on each LED and let it spread into the gaps. Once all the LEDs are glued, lay another piece of packing tape on top of the LEDs and push on each one lightly, so that the glue squeezes further between the gaps.
Do all 28 LEDs on the bottom panel, and all 14 on the middle panel. Again, observe polarity, and make sure you put the right colour in the right place. Once the glue is dry you may peel off the tape.
Step 7: Solder the LEDs
Conveniently (okay, it was planned), the leads of the LEDs overlap about a quarter-inch when folded flat against the edge of the plastic. The LEDs will be grouped into series chains as follows:
White LEDs: On each side, four sets of three, one set of two.
Red LEDs: Two sets of five, one set of four
In each set of two white LEDs, cut a gap between the leads of the LEDs, and solder a 150 ohm resistor between them.
In each set of three white LEDs, fold down the leads and solder the leads that stretch between the first and second LED. Cut a gap between the leads of the second and third LED, and solder a 68 ohm resistor between them.
In the set of four red LEDs (which is made up of two on either side of the panel), cut a gap between one of the pairs and solder a 150 ohm resistor.
In the set of five red LEDs, solder a 51 ohm resistor between the fourth and fifth LEDs.
It may help to mark which end of each chain is positive and negative - do so using a small piece of masking tape.
The LEDs will form a series-parallel network. Run lengths of wire in a daisy-chain to all the negative leads, and a separate wire to all the positive wires.
With everything wired up, you should be able to test the circuit. Use a 12V power supply, and observe correct polarity. Every LED should light up - if not, look for shorts and opens.
Lastly, run two main wires from the LED network, one for positive and one for negative. Leave a lot of slack, at least 18 inches.
With the LEDs all soldered, cover them all with another layer of packing tape so they are fully insulated.
Step 8: Taping the Bottom Layer
When the LEDs are soldered you can add the aluminum tape to the bottom layer. Basically the entire unsanded face will be covered in reflective aluminum tape. But, there's a trick here! (You may skip the trick portion if you're not using a capacitive sensor.)
The capacitive sensors require conductive electrodes to sense a change in capacitance. Luckily, the same aluminum tape we're using as a reflector can also be used as the electrode. But, you can't just stick it on and expect it to work. The electrode must be connected to the sensor, and not to anything else!
Fortunately, that's easy to do. Simply decide where you want the sensor to be, and stick the tape there. There are two sensors, one for the backlight and one for the subliminal message. I suggest using a smaller piece (perhaps 2" long) for the subliminal message, locating it somewhere clever. Behind that grey Serenity-shaped blob, perhaps? The sensor can be a bit bigger, maybe a 6" long piece of tape along the bottom. I chose to locate that sensor behind the text in the bottom left. If you like, you may use masking tape and the poster as a guide.
Now, simply fill in the rest of the panel with aluminum tape, being careful to avoid air bubbles. It's also very important that the electrodes do not touch the new tape you're laying down - allow a three to four millimeter gap on all sides of the electrode. Cover the gap with white electrician's tape or with a strip of cloth duct tape (gaffer's tape). This gap won't be too noticeable once the poster frame is done.
At the edges, fold the aluminum tape around to the other side, so that the tape just covers the LED body. Make absolutely sure that the aluminum tape is not shorting out the LEDs! Test the often as you work.
Step 9: Taping the Middle Layer
The middle layer will only have the outer edges taped with aluminum tape, so that the backlight can shine through.
Take strips of aluminum tape and cut them in half. Peel off the backing and frame all the way around the edges. As with the bottom panel, make sure the LEDs are not being shorted out.
Step 10: Combine the Layers
Take all three layers and the poster, and dry-fit them in the correct order. Try applying power to the middle and bottom layers to see the effect. When you're satisfied, set the top layer and poster aside for now.
The middle and bottom layers should be the same size. With electrician's tape, attach them together by folding tape around all the edges. You may also use the aluminum tape, but it's prone to damage.
Place the poster face-down on the top layer, and line it up so that an equal amount of plastic is visible on all sides. Tape it in place with masking tape. Flip the top piece over and set it on top of the middle and bottom layers. Try illuminating the bottom layer to help line up the poster. Tape all the layers together with masking tape.
In each corner of the poster, stick down a square of masking tape, and draw a crosshair about 5mm from each corner.
With all the layers temporarily held together, go to your drill press (or hand drill in a pinch) and *carefully* drill a hole in all four corners of the poster. The hole should go through all three layers of plastic and the poster's border.
Insert a screw in all of the holes, and secure with a nut. Don't overtighten the screw or you could crack the plastic.
Step 11: The Electronics
Now it's time to add some touch-sensitive wizardry! You could, of course, right up a simple toggle switch but that just isn't fancy enough.
The circuit itself is pretty basic. There are two halves, one for the white back light and one for the red subliminal message layer.
On the backlight layer, the capacitive sensor IC, upon detection of a touch sends a logic level "high" from its output pin. That signal goes to a D-type flip-flop which is configured (along with the assistance of an inverter) as an edge-triggered digital toggle switch. On each pulse from the sensor IC, the flip-flop's output toggles and latches in that state. That signal goes to a logic-level MOSFET which is used to control the current to the LEDs.
The subliminal message half is much simpler. The capacitive sensor is connected directly to the MOSFET, so that the LEDs only light when a touch is being sensed.
Also on the board is a small voltage limiter, that converts the 12V input to 5V for the capacitive sensor and flip-flop to operate.
Unfortunately the capacitive sensor is available only as a hobbyist-unfriendly WSON surface mount package. I knew I wouldn't have time to make a PCB, so I used a convenient little prototype board made by SchmartBoard. It has pads compatible with the WSON package, as well as numerous other package types. I simply chose components that would fit on the pad layouts available on the board.
Step 12: Assembling the Electronics
To do this you will need fairly advanced soldering skills and a decent soldering iron. The best way to describe the locations of the parts is via a picture, so check the photo below for guidance. I've included a high-res photo so that you can see every detail.
Start with the surface mount capacitors and resistors - they are the easiest to solder and are good practice if you haven't done surface mount soldering in a while (or at all). Do the DPAK voltage limiter next, followed by the slightly smaller SO-89 package MOSFETs. Then do the SOT23-5 flip-flops and inverters, and finally the capacitive sensors.
***A special note regarding the capacitive sensor IC. While these parts are compatible with the pin spacing of the SOT23 device, they have a ground tab on the underside that must be isolated or it may short out to the pins. If you have any, cut a small rectangle of Kapton tape and stick it to the underside to cover the ground tab. Otherwise, just use some masking tape.
Finish up by doing the point-to-point wiring, as necessary. This is where the schematic really helps - follow it carefully and you should be okay.
Position the board on the back of the poster and decide how you are going to run the wires from the LEDs and electrodes. When you're satisfied, cut wires that will reach from the board to the electrodes and solder one end onto the board. Then cut and solder the wires going to the LEDs.
Lastly, cut a pair of wires and connect them between the board and the power jack. Insulate the power jack with heat-shrink or electrician's tape.
Step 13: Mount the Electronics
Naturally we will want to safely mount the electronics on the back of the poster frame. I used two pieces of double-sided tape.
Take the two sensor wires and strip about half an inch of insulation off the ends. Unfortunately you can't solder them on to the aluminum tape electrodes, so we'll tape them on instead. Untwist the strands and fan them out, then tape them into the center of the electrode. Aluminum tape tends to stick better - just make sure it doesn't short out the electrode! A better alternative, if you have it, is to use conductive epoxy to glue the wire down.
Tape down the remainder of the wire for a neater appearance.
Step 14: Testing
Before plugging anything in, do one more check with a multimeter to look for short circuits and proper connections. Using the schematic as a guide, test between as many points as you can to ensure that everything is wired up properly. Make sure the electrode sensor wires are not shorted to anything. Most importantly, make sure there are no shorts from power to ground, on both the +12V and +5V lines.
Now, plug it in and see what happens. Be at the ready to yank out the cord should anything start to smoke (but nothing should, if your wiring is correct). Go ahead and test it - touch the sensors and see if the LEDs turn on.
I'll admit, it didn't light up the first time I turned it on. I had some wires in the wrong place (the perils of working till 2 am!). Then I discovered a busted capacitor. Finally, I realized that the inverter was open-drain, so it needed a pull-up resistor on its output. If yours doesn't work, you should be able to diagnose most issues with a multimeter. Simply test the voltage levels at each point in the circuit, and look for voltages that aren't what they should be. If you do build this project, I'd also be glad to help with any troubleshooting!
Step 15: Final Assembly
So!! Everything is working? EXCELLENT! The last thing to do is cover the back with something that will protect the electronics. I used a square of yellow craft foam, but you could use anything that lends protection to the board underneath, and is also non-conductive. This is very important, since any conductive object that comes near the sensors will activate them.
Now just hang your insanely complicated poster on the wall, ready to amaze your friends and incite feelings of intense jealousy!