coolguybri: cool light stand array

The cool light stand array integrates a set of Lego Power Functions Lights with an Arduino controller.

This was designed to be part of a Lego exhibition; it was placed around a larger exhibit to add highlighting and a little fun. Its functionality includes:

• Six individual light stands, each with two LEDs mounted on adjustable arms that allow them to be pointed in any direction.
• A control unit, where all six light stands can be individually turned on/off via push-buttons.
• A blink-mode button that can rotate between 6 different blink-modes, coordinated across the entire set of lights.
  • Constant All-On
  • Blink Fast
  • Blink Slow
  • UniDirectional Flow
  • UniDirectional Flow Slow
  • BiDirectional Back and Forth

• 6 Lego Power Functions Lights
  • bricklink catalog: Part 8870-1
  • Each Power Functions Light is actually two separate LEDs, connected together with a Power Functions adapter on the opposite end. The two LEDs in each unit are hardwired together and not independently controllable.


• 1 Arduino Mega 2560
  • I used this larger microcontroller board because I did not want to run out of i/o pins while hacking this up; however, the smaller and cheaper Arduino Uno has just enough pins to run this 6-light version.
  • You will need the Arduino Mega to extend the array to 8 lights (because the Mega has more i/o pins).


• 1 5-volt USB power source
  • Power source for the Arduino, connected via its USB port.


• 1 9-volt power source

  Power Functions circuits require 9 volts, but the Arduino controller only outputs 5 volts or 3.3 volts. We will use this power source to power the lights, and the Arduino will be used to just switch it on and off. Something like the image here, using the connector in red to connect with our circuit wires



• 8 S8050 D331 (NPN) Transistors
  • Used to manipulate the 9 volt output to the LEDs using the 5 volt control signal from the Arduino.


• 8 10K Ohm Resistors
  • Used to limit the current from the Arduino to the transistors.


• 4 Lego Power Functions Cables
  • bricklink catalog: Part 8886-1
  • Cut each of these cables in half, producing 8 halves.
  • For each half, cut off about an inch of insulation, exposing the wires that need to soldered to our circuit (see pinout below).


• 1 OLED Display
  • Displays the status of all the lights, and the currently selected blink-mode.
  • Also displays the build timestamp and the elapsed time since it last restarted.
  • Very useful for debugging while hacking it together.


• Lots of wire
  • I used 22 AWG solid wire for most of the Arduino connections, but switched to 22 AWG stranded wire for the lines out to each light (for better flexibility).
  • Should have gone with thinner wire; will do that next time.


• 7 push-buttons
  • 1 for each light, plus an additional button for the blink-mode selector.


• 1 Breadboard
  • Used to assemble all the electronic components.
  • Eventually to be replaced with a soldered circuit board for more permanence.


• DB25 connector
  • Allows easy disconnection of the controller box from the rest of the light array.
  • Useful for providing software updates or other maintenance of the controller, without having to move or adjust the lights.


• Miscellaneous Legos
  • Used to construct the structure of the controller box, and the light stands.

Note: the controller was internally wired to control up to 8 lights, so it includes 8 transistors and uses 8 output pins out to the DB25 connector and beyond. However, only 6 lights were actually wired up to the array before the project was completed (so two of the transistor sub-circuits are currently unused).

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Lego Power Functions Pinout

4 wires into a standard Lego interface used in all Power Functions modules 1 wire is common ground, 1 wire is a constant 9v, and the other 2 wires are used to control the lights; raising the voltage in either line will turn the lights on. This implementation always uses the C1 line and ignores C2.

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Controller DB25 Pinout

25 wires into the standard DB25 interface (used in old printers and other equipment from the 80s/90s) Outermost pins (13, 1) carry constant 5v and 9v power, with pins 25 and 14 connected to ground. Each light uses two pins, starting from pin 2, and pairing with the pin beneath it. (This was wired for 8 lights, even though the final version only has 6 lights attached to it). There are 5 unused pins, allowing up to 2 more possible lights with this design (for a total of 10).

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Arduino - Transistor - Light Circuit Pinout

Transitors are used to control the 9v lines (required to power these types of lights) from the 5v Arduino digital i/o pins. For each light, the Arduino output pin for that light is connected to the base of the transistor, via a 10K Ohm resistor. The transistor emitter line is connected to ground. The collector line is connected to the ground line of the light. The other pole of the light is connected to a constant 9v line. When the Arduino raises the voltage level on the base line, this opens up the transitor switch, completing the light circuit through the ground line, and allowing the 9v circuit to flow (and power the light).

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OLED Screen Pinout

4 pin interface 5v line and ground line are hooked right up to those same pins in the Arduino SCL and SDA lines are connected to the corresponding SCL and SDA pins on the Arduio; for example, on the Mega the SCL pin is digital pin 21, but on the Uno its implemented on analog pin 5.

• C/C++ using the Arduino SDK
• All the software is located at https://github.com/coolguybri/CascadiaControl/
• The main program file (and entrypoint) is located within that package at CascadiaControlGbc/CascadiaControlGbc.ino.
• The buttons, lights, and logging have been abstracted into a shared library, so this is where most of the application logic is located (including the blink modes). This can be found in the libraries/SeaRobLib/ directory.
• There is one external library used to help control the OLED display; this is the AdaFruit library, which is located across the libraries/ssd1306 and libraries/Adafruit_GFX_AS directories.