It's a display made out of 7-segment displays! This project was inspired by a similar project (https://hackaday.io/project/169632-7-segment-display-array-clock) from Hackaday user Frugha. They published their code and PCB design but I wanted to create my own version from scratch (otherwise where's the fun?!). Notably there were a few things I wanted to do differently:

• I used the TM1640 (https://www.lcsc.com/product-detail/C46683634.html) instead of the much more expensive MAX7219. Each TM1640 costs $0.15 and can drive 16 7-segment displays, versus the $1.50 MAX7219 which can each drive only 8 7-segment displays. With PCBWay's minimum PCB quantity of 5 that's a difference of $6.75 vs $135.
• The crystal, RTC, and MCU are soldered directly to the PCB instead of using bulky daughterboard modules, and I used a bare ATtiny861 instead of an Arduino Nano daughterboard.
• Hardware buttons for setting the time
• 3D printable enclosure

Font

The digits are generated by a C program which reads a .ttf font file, renders it to a bitmap, and calculates the appropriate 7-segment display segments to enable by considering the number of illuminated bitmap pixels that would lie within a given display segment. With this information it outputs a C header file containing an array that describes the font and is used by the firmware to render the clock digits. I've found that the display looks best using a bold+italic font. I used JetBrains Mono ExtraBoldItalic (https://www.jetbrains.com/lp/mono) but the font conversion program will work with any font. In fact it can render *any* glyph, it's not limited to digits. So you could make it display text too if you wanted. See the linked Codeberg repo for the font generation program.

BOM

• 3D printed parts from `mech/enclosure.FCStd` in the linked repo (created with FreeCAD: https://www.freecad.org)
• 6x M3x15 machine screws
• 6x M3x4x4mm heat-set threaded inserts (you can substitute another size and adjust the enclosure accordingly; see the `VarSet.threaded_insert_hole_diameter` variable in the FreeCAD file.
• 144x 12.6x19mm common anode 7 segment displays. Search eBay for "common anode 7 segment display" and sort by lowest price - you can get these in packs of 10 for less than $1.
• 1x DS1307 RTC (SOIC-8 package) + crystal. If you search eBay for "DS1307 module" you can find boards containing the DS1307 and a crystal for much cheaper than you can buy a single genuine DS1307. I used these and desoldered the crystal + RTC.
• LCSC parts from attached BOM.