If you come from a manufacturing environment, you’re likely familiar with PLCs — programmable logic controllers. Without going through the relative merits of this type of control system, one thing you will likely miss when working with Arduino and other development boards are the LEDs that light up when an output goes high. This gives you some indication that, yes, you are getting power to that relay (or other component) and you’ll need to wade through a jumble of ill-labeled wires with a voltmeter in order to kludge together a solution for your malfunctioning machinery.
Or perhaps your company features well laid-out machine control panels. Either way, these quick-reference lights can be extremely useful.
If you’d like to add this functionality to your Arduino board, the “LED Diodes Debugger Shield for Arduino” from Owl Labs is an interesting solution. It simply plugs into the I/O female header pins on one side of an Arduino UNO, and allows signals to pass through its own headers while lighting up to indicate what is HIGH and LOW.
It’s a great idea, and something that could even be an interesting concept to apply directly on a custom UNO-style board. Besides diagnostics, if you’d like to do a Knight Rider or Cylon lighting pattern, this would make things extremely easy!