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This is a remix of two great calendar Instructables. The first is the tomatoskins Automated Perpetual Calendar and the second is the cfb70 Cryptic Calendar.

I have constructed a number of manual perpetual calendars in the past. The big drawback has always been remembering to advance the calendar each day. I was hooked as soon as I saw the tomatoskins version. I quickly built one; substituting some 3D-printed parts for the original wooden parts. The calendar worked perfectly but I wanted to tweak a few things. The first was that when viewed from the side, the wiring was very visible. The second was that all of the circuit boards produce red LED light which glowed brightly against the wall. Lastly, the calendar is quite large; taking up a lot of wall space.

The cfb70’s calendar looks like a piece of abstract art using ancient or alien symbols. You really don’t know what you are looking at until the window frame slides into place and the digits magically appear. Again, the thing that I didn’t like was having to advance the calendar each day. By limiting the Days and Months to their three character abbreviations, it became possible to morph the calendars together.

I used the inverse of the Porker font identified by cfb70. Each inverse shape was expanded outward to a bounding rectangle offset from the original character and then offset again (made bolder) to help mask any minor rotational errors of the calendar rings. Each character was placed on its corresponding ring at the 12 o’clock position and then rotated about the ring center to its correct location.

The resulting calendar is 75% scale of the original tomatoskins version and features a completely enclosed housing. A small internal fan keeps the idling steppers cool. It can be wall mounted or it can mount to a stand. I used Autodesk Fusion 360 to design all of the parts. Autodesk is a great supporter of the maker community; allowing free use of Fusion 360 to hobbyists. I used Vectric V-Carve Pro to rout the rings and faceplate.



- (8) #8 x 3/4” Multi-Purpose Pan Head Screws
- (8) #8 Flat Washers
- (30) #6 x 3/8” Flat Head Wood Screws
- (4) #8-32 x 1/2” Truss Head Machine Screws
- (4) #8-32 Hex Nuts
- (6) M3 x 16mm Hex Socket Head Screws
- (2) M3 x 8 Hex Socket Head Screws
- (8) M3 Hex Nuts
- (6) M4 x 8mm Hex Socket Head Screws
- (6) M4 Hex Nuts
- (6) M5 x 20mm Hex Socket Head Screws
- (6) M5 Hex Nuts
- (3) M5 Flat Washers
- (4) M2.5 x 12mm Hex Socket Head Screws
- (4) M2.5 Hex Nuts
- (1) M2 x 8mm Machine Screw
- (1) M2 Hex Nut

Electrical Components:

- Noctua 5VDC fan
- HiLetGo Arduino Nano
- Stepper Motors and Drivers
- Hall Effect Sensors
- Real Time Clock
- Power Jack
- Power Cable
- USB Power Adapter


- Ferrules
- Heat Shrink
- Terminal Barrier Strips
- DuPont connector wires (various lengths)


- (1) 1/2” x 24” x 24” MDF Sheet
- 3-D Printer Filament
- (1) 1/8” (3mm) x 6” x 12” Acrylic Sheet
- (3) 3/8” diameter dowels cut to 3/4” long
- Magnets
- Hookup Wire

Major Tools:

- CNC Router with a minimum 18” square cutting area and a spoilboard
- 3-D Printer
- Drill Press or Hand Drill
- Table Saw or Hand Saw
- Oscillating Palm Sander
- Soldering Iron


- Laser cutter”

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