Programming the TFD 500

Protocol

(Thanks to Vincenz Dreger for reverse engineering and sending me the protocol.)

Caveat: please note that there seems to be no official documentation about the used protocol (but see “S” command below), and everything described here is the result of snooping the USB bus and analyzing the data when controlling the logger via the Windows software. So, the information here might be (partially) wrong and/or incomplete. Use at your own risk.

The built-in USB-Chip is a CP2102 from Silicon Laboratories (SiLabs).

ELV has changed the VID/PID to 18EF/E032. If you’re running on older Linux kernel, you might therefore need to use an updated kernel driver (cp201x) provided with the script on GitHub. Use lsusb to check if the TFD500 is known.

The serial interface parameters are 115200,8N1. The protocol is simple: the PC sends a command sequence to the logger and the logger answers with an appropriate message. All data transfers are in ASCII format with the exception of the actual data points, which will be sent in binary format.

The command sequences are case sensitive. Commands themselves are single characters and — depending on the command — may be followed by parameters. All parameters must be specified immediately after the command (no space between command and parameter, but there may be spaces between individual parameters). The response always starts with repeating the command character, eventually followed by the actual value of the response. The protocol does not use a start or stop byte.

The data logger can be read out during a recording but configuration can only be changed when the recording was stopped.

Known query command sequences

In addition to the above query commands, there’s another method to read the data records: if you send an “S” character, the logger immediately starts printing data records (as text using “OpenFormat”) until either the end or you send an “E” character. The following is an example output:

$N$;TFD500: 0xD762D0175B4F0F30
$I$;10000
$C$;Temperatur[°C,T];rel. Huminity[%];abs. Huminity[g/m^3];Dew Point[°C,DP]
$+28.6; 50;+14.05;17.2
$+28.7; 50;+14.12;17.2
$+28.6; 50;+14.05;17.2
$+28.7; 50;+14.12;17.2
$+28.7; 51;+14.41;17.6
$+28.7; 50;+14.12;17.2
$+28.7; 50;+14.12;17.2

And yes, as of version v01.00.05, there are spelling errors in the output (still not corrected in v01.00.06, a.k.a. v1.1.000).

As far as I know, LogView can be used to read this format. The python script does not use it (but it can also calculate approximate values for absolute humidity and the dew point).

Known configure command sequences