Powered Limit Switch

[Cash4587]

Can you run 12v through a limit switch legally to turn LED lights on and off by just putting the limit switch on the positive wire (or ground) between the PD Board and the LED?

[Al Skierkiewicz]

Under R52 in the 2013 Rules you may wire lights through a Spike.
"Each power regulating device may control electrical loads per Table 4-4. Unless otherwise noted, each power regulating device may control one and only one electrical load."
Following Table 4...
"*Multiple low-load, pneumatic solenoid valves or lights may be connected to a single relay module. This would allow one (1) relay module to drive multiple pneumatic actions or multiple lights. No other electrical load can be connected to a relay module used in this manner."
Limit switches have defined maximum current specifications that vary with model and type. It is not possible that we can say in your application that the limit switch can handle the switching current for the LEDs you want to use.

[Joe Ross]

Originally Posted by Al Skierkiewicz

It is not possible that we can say in your application that the limit switch can handle the switching current for the LEDs you want to use.

Regardless of current rating, isn't this illegal per R54?

R54

Custom circuits shall not directly alter the power pathways between the ROBOT battery, PD Board, motor controllers, relays, motors, or other elements of the ROBOT control system (including the power pathways to other sensors or circuits). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, if the effect on the ROBOT outputs is inconsequential.

[Jon Stratis]

Originally Posted by Joe Ross

Regardless of current rating, isn't this illegal per R54?

Would the combination of LED's + limit switch, taken as a whole, be considered a custom circuit? In other words, where do you define a custom circuit as starting and ending? Does it make a difference if it's a COTS LED strip, or individual LED's manually wired together (with appropriate resistors, of course)? If you define the system as two separate custom circuits, then it may be a problem. If it's just one custom circuit, then it's fine.

[Al Skierkiewicz]

Joe,
You are correct. I was addressing two issues without being clear. The first is strictly robot legal and the second that being after season bling. For robot legal, using a limit switch in this fashion is not acceptable. For after season it might be OK electrically, depending on the current demands and the switch rating.
As Jon points out, custom circuits do carry their own interpretation within the rules. Teams challenge us all the time with this. To be legal in season, LEDs that are part of a custom circuit can be used without Spikes. That is tallies for a controller, micro-computer or indicators on the custom circuit cannot be implemented using spikes or other power controllers. (much like the tallies on controllers) However, LED/LED Arrays for display or feedback to the drivers or for non-functional decoration of the robot in season must be controlled per robot rules.

[Tristan Lall]

I'm with Jon on this one—the custom circuit rules don't define where the circuit begins and ends, or which components can and can't be included. There's nothing inherently unsafe about it, but of course an unsafe implementation could be prohibited by the officials.

(The definition of custom circuit, and rationale for allowing things to be identified as such could stand to be clarified in the next iteration of the rules.)