Boards in 3 GitHub repositories, designed in KiCad, that use the MCP79510-I/MS by Microchip Technology (-40℃~+85℃ 1.2uA 1.8V~3.6V 1uA External SPI Temperature compensation、Backup power management and battery charging、InsideSRAM/NVRAM、Timestamp function、Programmable clock output、Alarm function、Power-off retention of registers、Locking and tamper-proof Yes MSOP-10 Real Time Clocks ROHS). See how each wires it, with its parts, size, README and files; the MCP79510-I/MS’s symbol, footprint and pinout are on its own page.
shilga/rp-gameboy-cartridge-hw
You should order with ENIG (electroless nickel immersion gold) plating. While the cartridge will work with HASL you will getter contact with ENIG and it is less prone to wearing down.
fachat/cbm_micropet
A small, single-PCB clone of the Commodore PET with all modern parts
fachat/csa_ultracpu
The CPU board for a 17MHz Colour-PET clone with modern interfaces