Remote-Url: https://mcuoneclipse.com/2022/01/09/diy-split-flap-display/
Retrieved-at: 2022-02-27 20:00:39.815504+00:00

Split-flap displays are electromechanical display devices, which were common in airports or railway stations a few years ago.Unfortunately, most of them are gone and replaced by LED displays. Why not create a DIY version of it?2×10 Split-Flap DisplayAs mechanical devices they are rather complex and subject of mechanical wear-out. But Split-Flap displays have many advantages over their LED counterparts: no power required if the display is static, good visibility and contrast, and the flapping sound draws attention if information changes.Luckily, there is anopen source project by Scott Bezekwhich helps you building your own DIY Split-Flap display. :-).Starting PointThe project started with a link a good friend forwarded to me (thanks again, James!), pointing to blog article by Dave Madison which shows how he has built a split-flap display:https://www.partsnotincluded.com/building-diy-split-flap-displays/8-Unit Split-Flap by Dave MadisonThis amazing project is based on the outstanding work of Scott Bezek:https://scottbez1.github.io/splitflap/If you need to know how such a display works:I really like his mechanical design, and with the needed equipment available (laser-cutter, desktop CNC,PnP, …) this project was in reach for me :-).The original project uses Arduino plus dedicated controller board. For many reasons I did not want to use Arduino. Instead, I wanted to build a system which can be used in the lab for my ‘Advanced Distributed Systems’ course, and this means using non-hobby software and development tools. Scott’s original design can drive up to 12 units, but I needed to have something which can be interconnected and distributed: giving each student one or more split-flap and have them connected and working with the units of other students. With this, I created a new driver/controller hardware and software.If you want to build your own: start with Scott’s excellent documentation. What I describe here is how I created my version, so you can decide and pick what you want to use for your own build. Ideally you are able to assemble electronics, have access to a laser cutter and/or CNC. If you don’t want to build everything yourself: Scott is selling components from his Etsy store too.EnclosureI re-used the original design from Scott with minor modifications, and created both 3 mm MDF and acrylic versions of it.For the MDF I used 60×60 cm sheets which get cut into pieces by the CNC:Cutting MDF sheet into piecesAlaser cutterthen cuts the parts out of each piece:Laser-cut MDFSimilar for the PMMA/Acrylic version:red PMMA piecesTranslucent red PMMA versionOne modification was to add a washer to every spool:Washer on SpoolI wanted to have a way to stack units:Stacking Split-Flap UnitsA 3D printed connectors keeps them on top of each other:To prevent the front plate nut from falling out the enclosure, it is kept in place with a 3D printed holder:Front Plate Nut HolderFront Plate Nut3D printed holders are used for the electronic boards behind the units. The holder simply get clipped between the enclosure units:Below the assembly of 20 split-flap units:Back of 20 split-flap unitsTo keep the motor cables away from the flaps, I have added a 3D printed cable tunnel:FlapsOne of the most important part of a split-flap are the flaps. I did experiment with aluminum flaps, but the sound of the flaps was not so good in my opinion.Experimental aluminum sheetsThe advantage would have been that they can be directly engraved with a laser cutter:Experimental Aluminum FlapsSo I ended up using PVC cards, the same kind of material which is used in Scott’s original project: Credit-card-size PVC cards which then can be cut to be used as flaps:Blank PVC CardsBut because of the ‘C’ for chlorine in PVC, it is very dangerous to cut them with a laser cutter. So instead, I used a desktop CNC to cut them.To cut the flaps with the CNC, I created a jig:Split-Flap JigUp to 10 PVC cards can be put into it:Cards to be put into the jigTwo pieces of MDF with screws keep them in place:Hold down with MDF and screwsThen the ‘tabs’ get milled out with a 1/8″ end mill. The result are cards with the needed cutouts:Cards with cut-outsCNC the flapsWith the masking tape which tightly keeps the cards in place, the result is clean and needs no real post-processing.Clean CutsBelow some of the cards cut with the CNC:PVC cards with cut-outsThe next step is to cut them in half.split-flaps ready to be cut in halfI did consider cutting them with knife or directly with the CNC. The best solution was to use a cutter which is used to cut wood or PCBs. A 3D printed jig is used to cut multiple cards in a single step:Cutting cardsBlank split-flapsLettersMany thanks to Dave Madison who created python scripts to create split-flap letters, which I used to create all the letters. Below the two lines to create two sets of letters I can cut with the CNC:python scripts/generate_fonts.py -t "ABCDEFGHIJKLMNOPQRSTU" --ncolumns 7

python scripts/generate_fonts.py -t "VWXYZ0123456789!?+.-#" --ncolumns 7This generates SVG files which can be loaded into Inkscape and then converted into DXF files: Make sure units are set to millimeters:InkscapeThen store the file into the .dxf format (File > Save As..). Here again make sure it is using mm:.dxf file with mm base unitsThen load each file into DXF2GCODE (see “Optimized Vinyl Cutting G-Code Tool Path with DXF2GCODE“) and create the G-Code files. Make sure to set the correct origin withOptions > Move Workpiece Zero(I’m using lower left corner):DXF2GCODEBecause I do the tool change manually, I have commented out the M6 (tool change command) in the resulting file(s).Cutting Vinyl Letters with Desktop CNCVinyl LettersThe letters then get applied to the flaps with a transfer foil:Cut-Out lettersadded transfer foilRemoving back-paperRemoved back-paperAdded flapsRemoving transfer foilApplied letterUsing the above process, it takes about 20-25 minutes to apply the letters for a single split-flap unit.Assembly in progressHardware: Motors, Nuts, …The motors (28BYI-48) are available in many stores. Make sure it is the 12V version:In general for all the hardware (nuts, …), I recommend you follow the guide on Scott’s GitHub Wiki:https://github.com/scottbez1/splitflapElectronicsA first proof of concept was pretty messy, but worked :-).Messy Proof of Concept of Controller SolutionSingle-Unit PrototypeBelow a first test with units:Because these days it is very hard to get microcontroller, and because most students already have atinyK22orLPC845-BRKboard, two designs around these boards have been created in KiCAD:tinyK22 Split-Flap PCBSplit-Flap Controller Board with tinyK22 and OLEDThe two boards are very similar: the main difference is if a LPC845-BRK (NXP ARM-Cortex M0+) or tinyK22 (NXP ARM-Cortex M4F) is used as MCU board.12V Power supply4 ‘breakable’ sensor PCBs for the hall sensorsJST 2.5mm connectorsRS-485 communication interfaceup to 4 split-flapstinyK22 version only: I2C (OLED) connector and UART for ESP32Split-Flap Controller board with LPC845-BRKThe sensor PCBs get detached from the main PCB.Sensor PCBsOn the back side, there is the through-hole hall sensor:Jig for soldering hall sensorFirmwareThe firmware is uses FreeRTOS with theMcuLiband is runs with the NXP MCUXpresso SDK and IDE:NXP MCUXpresso IDEThe firmware includes a command line interface, which can be used with USB-CDC, SEGGER RTT, UART, RS-485 or over WifFi with an attached ESP32. Text over multiple lines can be sent with a ‘\n’, e.g.will show the text on two lines.Shell Command Line InterfaceThe settings are storedin FLASH memory using key-value pairs. The position of each split-flap unit can be freely configured (x, y position on display).In case of missed steps of the stepper motors, the firmware is able to detect this with the magnet and hall sensor and automatically corrects it on-the-fly. For easy re-wiring of split-flap units, the firmware includes a pre-configured offset table, reducing the installation or reconfiguration time.Both the tinyK22 and LPC845-BRK version uses shared firmware sources. For a larger display the boards communicate over the RS-485, and the display content can be controlled from a single controller board, from the Host PC (UART, SEGGER RTT, USB CDC) or over WiFi with an attached ESP32. The tinyK22 boards can use a OLED (SSD1306) display too.SummaryCurrently I have 30 Split-Flap units assembled, with material for about 20 more units, so next step will be to build a larger display. With the RS-485 bus, there is a limit of around 128 devices (4*128 split-flaps) on a single bus, but then the 12V power monitoring and distribution would get  more challenging. Currently there is one MCU needed for 4 split-flaps: this is fine for the class environment, but for larger displays an overkill. Scott has been working on a chain-link version: a student just finished a similar project: driving larger displays with just a single MCU. More about this probably in a future article.I want to thank again Scott Bezek for his work and excellent documentation, which was a big help for this project.Happy flapping 🙂Links