The gbclock

A clock for your Game Boy!

• Accurate time from the RTC
• Day of the week
• Big numbers
• Vertical orientation
• Moving dot
• Hourly chimes
• It keeps the time even when powered off
• CC0

I think this is the first proper clock for the Game Boy. Other homebrew clocks use CPU cycles to keep track of the time, and that makes those clocks drift more than one minute per hour.

Requirements

gbclock requires a cartridge with MBC3 support and RTC

Tested with:

• Everdrive x7
• BennVenn's MBC3000 MBC3
• HDR's MBC3
• HDR's MBC30
  
• insideGadget's MBC3
• insideGadget's MBC3 4MB variant
• flash converted MBC3 cartridge (DMG-KFDN-10 with J.Rodrigo's adapter)

Not tested (yet) but it should work:

• EZ flash junior
  
• insideGadget's MBC3 RTC LinkNLoad USB Flash Cart 
• Bucket Mouse Game Boy MBC3 Cartridge
• other flashcarts with MBC3 support and RTC

I'm powering it with a USB to 3.5mm barrel jack cable with the polarity reversed (center negative), connected to an old phone charger.

Instructions

It will automatically show the clock at boot.

Press Select to set up the time.

Source code, assets and license

The source code and all assets used in the clock are available on github and published under the CC0. Feel free to customize and do whatever you want!

Other clocks for the Game Boy

• pixjuan's clockboy, made for GB Compo 21
• GBClock, Jeff Frohwein's talking clock from 1997