Split flap

Mechanical split-flap display

You can find full details and discussion on my blog.

This is an alternate electronics and firmware for David Kingsman's Split-Flap Display.

Advantages

• Only one microprocessor is needed to drive a 12 character display, instead of the 13 microprocessors that would be required in the original design.
• Off-the-shelf ribbon cables are used between PCBs to reduce custom wiring.
• All components are through-hole mounted (i.e. no SMD).
• Overall, this should reduce assembly time and effort.

Disadvantages

• PCBs are not mounted to the back of the display units but have their own mounting brackets. This approach is best suited for use in your own enclosure.
• A display of greater than 12 characters would require an additional controller board i.e. may not be as seamless as the original.
  
  

Settings

Turn on interactions and debugging over the USB serial port in debug.h:

DEBUG 1

Specify the number of Units (characters) in your display (4 -12) in system.h:

unitCount 12

Specify the network name of the display (useful if you have more than one display) in system.h:

NETWORKNAME "splitflap"

Customise for each unit for your build. (Units are numbered left to right 0 - 11) in unit.h:

calOffsetUnit : an array of the offsets to move from hall sensor trigger to blank flap
FlapStep : an array containing the number of steps per stepper revolution (then divided by 45 flaps)

Password and localisation settings in config.h:

WIFI_SSID "mySSID"
WIFI_PWD "myPassword"

MY_NTP_SERVER "au.pool.ntp.org" // Set the best fitting NTP server (pool) for your location
MY_TZ "AEST-10AEDT,M10.1.0,M4.1.0/3" // Set your time zone from https://github.com/nayarsystems/posix_tz_db/blob/master/zones.csv

WORDNIKAPIKEY "" // Get your private key from https://developer.wordnik.com/
MINWORDLEN 9 // Specify minimum word length to fetch from Wordnik
WORDUPDATESPERHOUR 1 // Set number of word updates from https://wordnik.com per hour. 0 will disable, else use an integer that results in an exact number of minutes btw updates i.e. 1,2,3,4,5,6,10,12,15,20,30 or 60

Libraries

This project makes extensive use of two libraries:

• FastAccelStepper by J.Kiemes
• arduino-mcp23017 by Bertrand Lemasle
  
  

Connecting to the display

There is a very basic web page served at http://splitflap.local/ to allow you to either enter text to display or fetch a random word from Wordnik

There is also an API endpoint that you can POST to at http://splitflap.local/display, using a JSON payload in the body:

{
    displaytext: "Display Text"
}

For example, you could use the request node within node-red:

PCBs

Schematics for the Controller and Unit PCBs can be found under schematics.

Gerbers, Bill of materials and Kicad source files can be found under PCBs.

Brackets & unit frames 3D printing

PCB mounting brackets can be found on Printables.
Also found there is my remixed unit frame. This is optional, as you could still use the original frames with the new electronics. My unit frame requires an additional two M3*L3*D4 heat inserts for connecting to the adjacent unit.

Enclosure (laser cut)

front

rear

Plywood (3mm) files for laser cutting are in enclosure

Licensing

Copyright (c) 2024 Malcolm Yeoman.

Electronics is released under CERN-OHL-P (Permissive) V2.
Firmware is released under the MIT License.
Documentation is licensed under a Creative Commons Attribution 4.0 International License.