Programmatically talking to a Serial Port in OS X or Linux


I have a Prolite LED sign that I like to set up to show scrolling search queries from a apache logs and other fun statistics. The problem is, my G5 does not have a serial port, so I have to use a usb to serial dongle. It shows up as /dev/cu.usbserial and /dev/tty.usbserial .

When i do this everything seems to be hunky-dory:

stty -f /dev/cu.usbserial
speed 9600 baud;
lflags: -icanon -isig -iexten -echo
iflags: -icrnl -ixon -ixany -imaxbel -brkint
oflags: -opost -onlcr -oxtabs
cflags: cs8 -parenb

Everything also works when I use the serial port tool to talk to it.

If I run this piece of code while the above mentioned serial port tool, everthing also works. But as soon as I disconnect the tool the connection gets lost.


import serial

ser = serial.Serial('/dev/cu.usbserial', 9600, timeout=10) 
ser.write("<ID01><PA> \r\n") 
read_chars =
print read_chars


So the question is, what magicks do I need to perform to start talking to the serial port without the serial port tool? Is that a permissions problem? Also, what's the difference between /dev/cu.usbserial and /dev/tty.usbserial?

Nope, no serial numbers. The thing is, the problem persists even with sudo-running the python script, and the only thing that makes it go through if I open the connection in the gui tool that I mentioned.


have you tried watching the traffic between the GUI and the serial port to see if there is some kind of special command being sent across? Also just curious, Python is sending ASCII and not UTF-8 or something else right? The reason I ask is because I noticed your quote changes for the strings and in some languages that actually is the difference between ASCII and UTF-8.

/dev/cu.xxxxx is the "callout" device, it's what you use when you establish a connection to the serial device and start talking to it. /dev/tty.xxxxx is the "dialin" device, used for monitoring a port for incoming calls for e.g. a fax listener.

Your best researching the most common type of queries that happen on your database and creating indexes based on that research.

For example, if there is a table which stores website hits, which is written to very very often but hardly even read from. Then don't index the table in away.

If how ever you have a list of users which is access more often than is written to, then I would firstly create a clustered index on the column that is access the most, usually the primary key. I would then create an index on commonly search columns, and those which are use in order by clauses.

This video can help you solving your question :)
By: admin