Electronics Bash – #15 – Long Distance Signals

We’ve got a couple ways to pass signals between Arduinos sitting next to each other on the workbench now, or even 50′ away via a wireless dongle. But what if you need to get signals from 1000′ away or more?

That’s where a robust wired system based on RS485 can help. As a physical protocol, RS485 won’t get you there alone – you’ll need a communications protocol built on top of it to actually pass data. This week, we’ll look at DMX, the most common control protocol in the entertainment lighting field, how it relates to DMX , and how you can use both to pass messages long distances.

Topics Include:

  • RS485 fundamentals
  • The OSI Model
  • DMX (Digital Multiplex)
  • Network Topologies
  • Singalling and Addressing schemes
  • Transmission lines, impedance, and ternimation

Code Libraries

This week we’ll be making extensive use of the Conceptinetics DMX Library to handle DMX communication. You can download it from the link above. There are several published libraries that handle DMX, but this is the one I’ve had the most success with.

Code

The following code will make use of the above circuit diagram
This following code will also be used with this circuit diagram.

Basic Send

Basic Receive

Knob Send

The following code will use the above circuit diagram

DMX Basic Send

DMX Basic Receive

DMX Knob Send

DMX Knob Send Dual