Many of the devices that SOWN uses can be accessed using a serial connection instead of the monitor and keyboard that you would use to connect to a regular PC. Setting up the physical connection to a particular device can be found on the device's page. This page deals with configuring your computer to make a serial connection.
The recommended client to use is Putty. If you use Windows XP or earlier you may want to use [Hyper Terminal]. Putty is commonly used for SSH connections but can be configured to use your serial port. It works on Windows, Unix/Linux and also probaly on MacOS?. For more details on obtaining and configuring Putty see this page.
Serial connections require 4 software configurable settings to work. They also require the correct voltage.
These settings are are normaly given on the device itself. The settings are often given in the form a b c d. Where a is the bit rate in bits per second. b indicates the number of data bits being used. c indicates what parity is being used. d indicates the number of stop bits. For example
9600 8 N 1
Indicates a device communicating at nine thousand six hundred bits per second with eight data bits no parity and one stop bit.
This is the rate at which data is sent to and from a device.
Table of common settings
|Bit Rate||Common uses||Uses in SOWN|
|4800||NMEA GPS||Location finder|
|9600||Probably most common speed for configuring serial devices||ALIX boards|
|115200||High speed serial, fastest speed supported by older devices. Its like nearly 2x the speed of dialup!!!||Meraki|
Number of Data Bits
This is the number of bits in each packet which contain the data being transmitted. This is almost allways 8.
This setting determines what type of parity is used. This is importan on serial links where data may become corrupted as it allows you to verify the integrity of the data. Most modern serial communication is done over distances of less than 10m so corruption of data is unlikely to be a problem. As a consequence allmost all serial devices have no parity set.
Number of Stop Bits
This is the number of bits which follow the packet and do not contain data. This prevents the packets running into eachother and also gives the devices some time to rest. As modern devices are fast enough to handle serial communication effortlessly and communication distances are short this is almost always set to one.
The RS232 Specification specifies transmission of +12v for a 0 and -12v for a 1 or idle. The devices themselves must accept a diviateon as small at +3v to -3v. Even this is too much for devices like the Meraki which do not possess a -v rail so it is neccecary to build a conversion curcuit to convert from +3/0 to +12/-12.
To list the serial output of a device eg GPS receiver you can cat the serial port as follows:
You will first have to set the port speed using the following command:
stty -F /dev/ttyUSB0 4800
This will set the port speed to 4800 - the speed of NEMA GPS.