Can I add a GPS module to this clock?
How can I program the chip/firmware?
You may also have to remove the tube to program it (we had to with the USBtinyISP). If you're using a USBtiny, jumper the 1.5k output resistors (check the usbtiny docs for information on how to do this). We dont guarantee that you can program the clock in-circuit so experimentation is key!