Fineline was approached to design and manufacture an LED chandelier consisting of a number of large spheres suspended at different heights from a ceiling-mounted structure. Each sphere was to be illuminated from within using colour mixing LEDs, allowing the colour of each sphere to be independently set. The entire chandelier was to be controllable via DMX.
Fineline Manufacturing undertook to provide the structure and spheres; Fineline Solutions designed and produced the dimmer modules. The requirements for the dimmer modules were as follows:
- Robust construction
- 24V DC power supply with reverse-polarity and overcurrent protection
- DMX address configurable using DIP switch
- Self-test mode
- DMX input
- Buffered DMX output
- Control for 7 spheres (21 LED dimming channels)
- Constant voltage dimming
Each sphere contained several lengths of three-colour LED tape, arranged to ensure even illumination within the sphere. For ease of connection, the tape was attached to a length of Cat 5 cable with a standard RJ45 connector.
An extruded aluminium enclosure was chosen for the dimmer module, which effectively dictated the size of the PCB. RJ45 connectors were provided for connection to the LED spheres, DMX input and DMX output. A DIP switch allowed the installer to set the DMX start address, and a 2-pin connector was provided for connection to the power supply.
Two of the most common causes of failure of LED dimmer modules are caused by incorrect power supply polarity, or a short-circuit on one or more outputs. To protect against this, a reverse-polarity protection circuit was integrated, along with a self-resetting fuse.
A PIC microcontroller was chosen as the basis of the dimmer, and was used to receive and decode DMX data. Based on the start address, the microcontroller was used to vary the brightness using pulse-width modulation. A set of simple output drivers were used to provide up to 500mA current-switching capability to each of the 21 dimmer channels, although in reality no channel would draw more than 50mA in operation.
To aid installation, a simple self-test mode was added, which allows the red, blue and green channels to be operated independently. A simple colour roll was also provided for demonstration purposes.
This dimmer module is also available for sale as a stand-alone product.
For further information, or to discuss a similar project, please contact Fineline Solutions.