Metlink LED passenger information display driver
The metlinkpid module provides a class to operate Metlink LED passenger information displays:
>>> from metlinkpid import PID >>> with PID.for_device('/dev/ttyUSB0') as pid: ... pid.send('12:34 FUNKYTOWN~5_Limited Express|_Stops all stations except East Richard')
It also provides a function to inspect raw display data, both with and without checksumming & packet-framing:
>>> from metlinkpid import inspect >>> inspect(b'\x10\x02\x01\x44\x00\x1D\x00\x00\x00\x4F\x50\x45\x4E\x0A\x46\x4F\x52\x20\x42\x55\x53\x49\x4E\x45\x53\x53\x0D\x8F\xDF\x10\x03') DisplayMessage.from_str('V0^OPEN_FOR BUSINESS') >>> inspect(b'\x01\x44\x00\x1D\x00\x00\x00\x53\x54\x49\x4C\x4C\x20\x4F\x50\x45\x4E\x0A\x46\x4F\x52\x20\x42\x55\x53\x49\x4E\x45\x53\x53\x0D') DisplayMessage.from_str('V0^STILL OPEN_FOR BUSINESS') >>> inspect(b'\x01\x50\x6F') PingMessage(unspecified_byte=111)
Find the device
Determine the device to which the display is connected. On Linux, this can be achieved by disconnecting the display from the computer & reconnecting, then inspecting the contents of dmesg output for USB attachment messages:
[ 3.010816] usb 1-1.4: FTDI USB Serial Device converter now attached to ttyUSB0
The above output indicates that the display is reachable through /dev/ttyUSB0.
Display a message
Next, write & run a Python script that connects to that device location and calls PID.send():
from metlinkpid import PID with PID.for_device('/dev/ttyUSB0') as pid: pid.send('12:34 FUNKYTOWN~5_Limited Express|_Stops all stations except East Richard')
The PID should display the specified message instantly, but after approximately one minute the display will self-clear.
Keep the message up
To prevent the message from clearing, the display can be pinged at a regular interval:
from time import sleep from metlinkpid import PID with PID.for_device('/dev/ttyUSB0') as pid: pid.send('12:34 FUNKYTOWN~5_Limited Express|_Stops all stations except East Richard') while True: sleep(10) pid.ping()
Use the | character to separate pages of a message:
The message in the above send() call has three pages: V10^FIRST_PAGE, V10^SECOND_PAGE, and V10^THIRD_PAGE.
Everything in a page up to and including the ^ affects the display of the page, and is not included in the output. The letter specifies the animation and can be V for a vertical upwards scroll, H for a horizontal scroll, or N for no animation. The number specifies the delay (in roughly quarter-seconds) after the animation finishes and before the next page (or first page again) is shown.
Text after ~ will be right-aligned on the current line, and text after _ will appear on the next line. Each page in the above example therefore spans two lines.
Some ASCII characters are not available for display, and some “extended” Unicode characters are available. Full details are in the documentation for the Page class.
- Animation types
- Not all known page animation types are implemented yet.
- PID class unit testing
- Unit tests have not yet been written for the PID class. A suitable serial port mocking interface is yet to be found.
The metlinkpid module is fully documented. All further usage & development details can be found in the documentation. Bug reports, feature requests, and questions are welcome via the issue tracker.
- Add optional ignore_response parameter to allow PID response errors to be ignored.
- Add support for Python 3.6.
- Initial release.
Pull requests for both code and documentation improvements are gratefully received and considered.
This project is licensed under the MIT License.
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