Baud Rate Backgrounder

overview

• Wikipedia on RS232
  

Just wanted to do a very rough overview here with more of a focus on baud rates (data transmission speeds) and why you might choose one of another depending on your circumstances.

Getting into it.

When it comes to telemetry and communicating a lot of our work makes use of the RS-232 protocol. Protocol in this context means basically a standard. RS232 is a standard way of doing machine to machine communications. At the base level it takes three wires. A transmit wire, a receive wire, and a common ground. That is the simplest. As you try to communicate faster and with more reliability more wires can be involved. Within the context of communicating with remote sites there are a few general rules of thumb.

• if you are using an older data logger then 9600 baud is typical.
• If you are transmitting pictures over a radio network then faster is better. 115,200 is the top speed for rs232
• if you have a radio network passing this data, once you introduce 'repeaters into the network then the top speed typically is reduced to 57,600 (for freewave units... see the manual)
• if you have an unreliable radio link it is possible that you can increase the performance of your network by slowing the baud rate. This is because as you get slower the bit
• if you are logging GPS data the minimum baud rate you should select is 38,400 to ensure there aren't gaps in the data caused by too much data trying to be pushed through in a second. (There are some USGS guidance documents on this).