A serial UART can handle multiple devices, with an appropriate protocol and interface. E.g. EIA-485 or the equivalent with different drivers/recievers.
With UART I was refering to the standard serial port of the Atmega32u4 that uses RX and TX which you canāt just tie together without additional hardware.
i2c is cool and supports lots of things you can do link cable and also works in salt water
Itās minor, but IĀ²C requires pullup resistors, which is additional hardware.
Also, for SPI (and possibly IĀ²C), Iād be wary of just tying the pins of two or more Arduboys together. If one Arduboy has a full charge, Vcc to the MPU could be at 4.2V. If the other Arduboyās battery is nearly discharged, its Vcc could be 3V. Thatās a 1.2V difference. I wouldnāt want output pins at 4.2V feeding inputs on an MCU powered at 3V.
With IĀ²C, pins are pulled high through pullup resistors. Depending on their values, they might limit the current and make it safe to tie a fully charged Arduboy to an almost discharged Arduboy.
Also, SPI would require another line in the cable for each additional device attached.
(The Arduoboy Mini will be safe because it has an LDO regulator for the qwiic/IĀ²C interface but that makes these regulators additional hardware.)
On topic a little more: I think your homemade one looks incredible especially for being through hole components. That was a great entry to the hackster contest!
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internal pullup ar good enough for short distances. No additional hardware needed 
Thanks! the idea was too use through hole only so it would be easier to build by others.
Updated the bootloader to use larger graphics stored on external flashchip. Basically all the data used to display the date and time is stored there so itās fully customizable now.
Itās already supported by the Cart Builder website.
A python script to patch/update exisitng flash images with custom
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By āun-bakingā the bitmaps from the firmware, will it allow easier customization?
Iād prefer a far small / discrete clock for my personal use.
c.f. Apple still doesnāt allow custom watch facesā¦ 
I may or may not have been putting pressure for the ability to customize the font by virtue of me not being able to decide what would look best for the platform default. The fact that any of this is possible in less than the space than the default bootloader is just - magic.
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Yes. you supply images in the same naming convention as my python image converter script handles and thereās a text file in ini format that allowes you to put any date/time digit at any positon on the display.
Only restriction is they must have a height of multiple 8 pixels and be positioned at a multiple of 8 vertical pixels. Sprites have no masking feature and all the sprites combined may not take up more then ~1200 bytes.
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This sounds like a great feature! Thanks!
BTW- Why GT ā¦?
Game and Time 
Damn, I thought it was a Dragon Ball GT reference.
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