Ho John Lee’s Weblog

I have used various heart rate monitors and GPS-based distance measuring systems as part of my running in the past. A couple of years ago, I wore a Timex Bodylink HRM and GPS system, with the data recorder, during the Big Sur Marathon. Since I’m a bit of a data junkie, I wanted to compare the race data with my previously recorded training data.

Unfortunately, the Timex Trainer software choked while downloading the 4+ hours of data. It did let me download the raw data from the recorder, though. I was hoping that someone at Timex might be able to either parse the data or provide a specification so I could process the bits myself. Other than signing up as an OEM developer, there wasn’t much in the way of software support, and no useful response from Timex with regard to either recovering the data from the binary dump (eeprom.txt) or getting a specification.

I never got around to fully decoding the raw data dump format, but thought I would share my notes for anyone who is interested in picking this up. At present, I can read the session directory, and the heart rate data. The GPS data encoding is more complicated, and may use the native encoding from the GPS chipset used by the (Garmin-manufactured) Timex GPS pod (might be SIRF).

From viewing the Timex Trainer database (Microsoft Access format):

• we can see that all HR data times are integer multiples of 2 seconds
• no HR data times are recorded on odd seconds
• HR records store prkey, sessionkey, cum_duration(int seconds), and HR
• HR only session is session_type 0, GPS only is session_type 1, combined is session_type 20
• all GPS data times are exact multiples of 3.57 seconds
• GPS records store prkey, sessionkey, cum_duration(float seconds), speed, and cum_distance
• minimum recorded distance is .001 miles
• before that cum_distance is 0>
• minimum recorded speed is 0.075
• we see cases where speed is non zero and cum_distance is 0
• we see cases where speed is zero and cum_distance is non-0

Dump header format (eeprom.bin / eeprom.txt)

• 2 bytes = 80 01 magic number?
• 3 byte offset to end of session N
• repeated for each session.
• 1st session starts at offset +240 from top of file.

Session header and trailer:

• 1 byte = session type (0 = HRM, 0×22 = GPS, 0xFF = GPS+HRM)
• 1 byte = seconds
• 1 byte = minutes
• 1 byte = hours (24 hour format)
• 1 byte = day-1 (1st = 0)
• 1 byte = month-1 (Jan = 0)
• 1 byte = year-2000 (2004 = 4)

See also: Hacking the Timex Bodylink - Part 2

This entry was posted on Thursday, September 8th, 2005 at 11:58 am and is filed under Running, Front Page. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.