Answered: Using transistors as a component of a non-functional decoration

Hey VEX Support. I am here musing on the legality of implementing transistors in conjunction with LED lights for the purposes of their control from the Vex Cortex digital ports.

In the past our team has made use of LED light strips as a non-functional decoration. We have in the past simply used non-individually addressable strips with their included controllers and connected them to the 5v and GND rails of a digital port so that they would power the device. There isn’t a ruling on the legality of this, however we used heat-shrink over the connection and a VEX cable and header in order to achieve this. As far as we know, the legality of this has not yet been questioned. This is similar to the methodology used by @thedude019 here.

This year, we have ventured to using similar RGB LED light strips, however we have also decided we wish to control their function from the cortex. These lights work with a common 5V and to control the RGB components of the LED we pull their respective ground rails down.

One way we could achieve this is to use the motor ports, as we have found they can supply more current and voltage than their ‘GPIO’ counterparts. However, upon speaking with our group of builders they were less than happy that I would hijack 3 of their motor ports in order to achieve the full range of colors we were hoping.

The second option then presents itself as making use of the digital ports, however upon experimentation and some reading (see here) we discovered that the current potential (get it?) of the VEX digital ports is less than exciting for a strip of RGB LEDS!

While we could simply stop here and connect the 5V and GND up to a color of our choice, we wish to use an external circuit (a few transistors inside a sealed enclosure) in order to drive this non-functional decoration - as we could assume that this circuitry would fall under the same guise (of a non-functional decoration). This is primarily so that we can use a bit-banged PWM on the digital outputs and achieve a few million colors as well as dimming and basic control of whether the LEDS are on or off at any one point without having to add additional circuitry.

There was some circuitry described in these two threads (one of which, I actually commented on in the past, ahah): Digit port power address and LED Strip Help - Dim lights???. However it was ruled as ‘probably not legal’ and I can’t find any continuation of this idea. I would think that this is no more an issue that using LED lights with such circuitry integrated.

So my question is whether the use of external circuitry for the purposes of controlling a non-functional decoration is legal in VRC Competition.

I have attached any relevant rules from the manual below.

Thanks for your help in advance!

Yes, this is legal, provided no other rules are violated in the process. We would advise you to keep the following caveats in mind:

  • Please remember rule S1 at all times. If any element of the system is deemed unsafe by a referee or inspector, they will have the final jurisdiction at your event.

  • In order to be considered a non-functional decoration, the LEDs must not affect robot performance or affect the outcome of the match in any way. If an inspector or referee determines that the lights are being used to provide any sort of feedback to drive team members, they would no longer be considered “non-functional”. We would recommend using a uniform or static pattern to help avoid this perception.

  • It sounds like you’ve done your homework in developing this creative solution within the rules. However, for the sake of being thorough, please remember that in order to be considered legal, this must be done without modifying the Cortex or other electronics (R15), drawing power from an external power source (R13), or violating any other Robot rules.