Python libraries for generating and transmitting data to the Timex Data Link series of watches using optical data tramsission, an Arduino sketch fully able to replace the Notebook Adapter as well as work with this library, and software for capturing and decoding packets from the original software.
Currently, the protocol for the original Data Link (50 and 70) is implemented fully, the 150 and 150s partially, and the Ironman Triathlon is being worked on.
There is a guide [written by dfries] (https://github.com/dfries/datalink_ironman/blob/github_submodules/datalink/70.txt) on the Data Link packet encoding. This information was verified using the original software, and a few errors were corrected. The data was collected using the included script timex_notebook_adapter.py, which emulates the Timex Notebook Adapter and logs all bytes sent from the program. Much easier than getting it from the CRT!
More specific work:
A device for sending data to the watch if you don't have access to a CRT monitor. Connected via serial port and powered by the CTS line. Initially responds to commands "x" (reply with "x", used for identification), "?" (reply with "M764\0", probably some kind of model name) and 0x55 (enter send mode, actually the first sync bytes sent). After 0x55 is received, all bytes are sent over the IR LED. To get back to the initial state, device power must be cycled. This is done by pulling CTS low for a few hundred milliseconds.
When a byte is sent to the adapter, it replies with the same byte to keep things in sync.
Since I do not have access to an actual adapter, I have no way of verifying the timings of the device. It's a safe bet, though, that they will be very similar to those from the CRT. It is also possible the data could be sent somewhat faster since it does not need to be phase locked to the CRT refresh.
Arduino code for the above protocol is available in timex_transcoder.
It works both with the Pyhton code, and with the original Timex software
using an RS232 to UART converter.
To use it you need an Arduino with ATmega328 (168 would probably work too) with 16 MHz clock. Should work with Uno, Nano, Duemilanove and others. Connect a bright LED to pin 12 (maybe with a suitable resistor in series) and that's it.
Experiment with distance and intensity to get it just right. Some LEDs are very focused and offers only a narrow beam, and might saturate the receiver.
What ultimately worked best for me was to use a high-intensity white LED without a resistor and shine it onto a surface. That way, the angle and position of the watch didn't matter as much.