Summary

I produced Christmas lights to be displayed at my home.

Purpose

Using full-color LEDs that can be controlled via serial communication, I attempted to create a light effect that was difficult to express with ready-made home-use illumination at the time.

Development Process

Making Image Sketch

To ensure a large flat surface (=canvas), a metal net was set up on the terrace of my house, on which the electric lights were fixed.

Selection of LED Lights

The requirements were 1) the LED color must be individually controllable via serial communication, and 2) the LEDs must be waterproof for outdoor use. After considering price and performance, a product was purchased from China. Two types of lights were selected: LEDs with diameter of 10 mm for pixie dust and snowflakes, and LEDs with diameter of 30 mm with a milky white cover for the background of the canvas.

Making Snowflake Ornaments

The shape of the ornament was designed using CAD, and the acrylic panels were cut using a laser cutting machine. A total of six snowflakes wereproduced (two of each of three different designs), and all ornaments have two layers. The first layer has holes for inserting LED lights, and the second layer is installed via spacers. Acrylic panels with uneven surfaces were used to diffuse the LED light as much as possible and to allow the light to reach the entire acrylic plate.

Control System

A control box was created to control all the LEDs. The LEDs in this work are divided into a total of seven strings. Eight microcontrollers are used to control the work, with seven follower microcontrollers to control each LED string and one main microcontroller to oversee them. Serial communication is possible between microcontrollers, and each follower microcontroller controls the lights at its assigned location based on commands from the main microcontroller. The power supply for driving the LEDs is provided by a switching power supply and distributed by terminal blocks. Considering the amount of current flowing in the wiring, the power supplies were distributed to three units.

Wiring Work

At first, a metal net was installed on the terrace, and LEDs and snowflake ornaments were fixed on it with cable ties so that the design would be as shown in the image skech. Although each LED has a cover to diffuse the light, the LEDs are highly directional, so the brightness of each LED will not be consistent unless the LEDs are oriented properly. Therefore, the LEDs were fixed so that all the lights were oriented in the same direction.

The next step was to wire between each LED and the control box. The wiring was done along the edge of the terrace fence, keeping in mind that the wiring should look neat. In addition, the wiring connections are waterproofed. A household timer was used, and power is automatically supplied at a preset time.

Software

The control method was determined. Each follower microcontroller has multiple lighting patterns programmed in advance and changes its operation according to the command values sent from the main microcontroller. The data sent to the follower microcontrollers for the snowflake and background LEDs is 1 byte long, with the upper 3 bits being the address of the slave, the middle 3 bits being the color of the lights, and the lower 2 bits being the lighting mode. For pixie dust, the effect is constant and only the color can be changed.

Operation Testing and Fine-tuning

1. First, the sample program was written to each microcontroller, and it was confirmed that the LEDs in each part worked without any problems.

2. Next, a pre-made program was written, and the operation of each part was tested and the brightness was adjusted.

3. Finally, after confirming that each unit was operating stably, an overall integration test was conducted. Since it was confirmed that each follower microcontroller responded to the transmitted data without problems, the performance pattern was adjusted by tuning the source code of the main microcontroller in this work. The data sent to each follower microcontroller and its timing were adjusted to ensure that the intended scenario was executed. The adjustment work was conducted from inside a car because it was midwinter and very cold.

Future Task

The control of the LED with a 30 mm diameter and white cover used for the background was not stable. The LEDs did not change to the color specified in the program or flashed irregularly. I suspected a lack of current that the power supply could provide and defects in wiring contact, but in the end I was unable to solve the problem during the exhibition period. Later, I obtained information that similar problems may occur depending on the type of LED control libraries. I would like to verify if the condition can be improved by changing it.

Experience

• Experience working with power that is greater than usual electronic work.

• Experience in synchronizing multiple microcontrollers to create a single production.

• Experience in selecting wiring, power supplies, and other equipment, taking into account power consumption and amounts of current.