Most of the mods you'll find are going to require reprogramming the clock firmware. To do that you will need an AVR programmer with a 6pin ISP cable ($20-$50), AVR software (free) and a computer.
The generic instructions for reprogramming the clock:
- Remove the power
- Carefully disassemble the plastic case
- Then remove the tube and put it away in a safe place
- Connect the 6 pin ISP cable from the programmer so that the red wire lines up with the corner that has a circle silkscreened on
- Hint! If you are using a USBtinyISP, remove the power jumper and make sure you have R4 and R7 jumpered as well (not 1.5K resistors)
- Power up the clock with the plug adapter
- Use the command avrdude -c usbtiny -p m168 -U flash:w:newfirmware.hex or similar to update the firmware
- Remove the programming cable, and reattach the tube. You may want to check that the firmware did what you wanted
- Reassemble the case
Of course, who doesn't want satellite-precise timing? This firmware mod allows you to add any 4800 TTL NMEA GPS module. Check that the module can run from 5V power, and has a wire that outputs NMEA 4800 baud at TTL levels. Do NOT use any RS-232 level outputs, they can easily damage your clock!
These code mods are by Devlin Thyne!
Download the latest firmeware from github (the Ice Tube Clock GPS fork), here is a direct link to the iv.hex you can save as...
First step is to get a GPS module. As we mentioned before (but its worth mentioning again) make sure it can run from 5V power, and has 4800 baud TTL NMEA output. Nearly all hobby GPS's do. We'll be using a fairly low cost GPS module from parallax (the PMB-648)The nice thing about this one is not only does it work great but has long enough wires.
Identify which wires are for ground (usually black), power (usually red) and TTL data out (yellow in this case). We cut the other wires, you can also just tie them off and make sure they dont short against anything. Check the GPS module's datasheet of course!
Thats it! Your clock now has the correct time and date at all times. If you ever see any drift, just stick it near a window for a bit until it resets itself.
If the clock seems to be resetting randomly, it could be that the GPS is drawing too much power and resetting the fuse. Replace the fuse with a 300mA version.