Geodesic Light Dome

Page last updated 19 Mar 2010, by Peter Cooper. 0 replies CAN, ethernet, I2C, mbed, RS485/RS422

See http://www-users.cs.york.ac.uk/~pcc/Circuits/dome/

 

One of our accademic research staff  has asked us to look at a Geodesic Light Dome, a wire frame dome with lots of lights, and the ability for each light to be controlled via a computer, ro the research group can control light levels on three-D objects

The Image to the right is not ours, we hope that in time we can replace this picture with a picture of our dome, watch this space

And we all like flashing lights :-)

Early tests where done using a 16 channel I2C lighting controler, and a USB to I2C interface chip produced by a group called HexWax, some example code of ours can be found hare from the early tests for the project



Version 2 of the controler uses a much better controler chip A PCA9685 See here for the new basic test design (from Oct 2009).

  1. 16 LED drivers. Each output programmable at:
    2. * Off * On * Programmable LED brightness * Programmable LED turn-on time to help reduce EMI
  2. 1 MHz Fast-mode Plus compatible I2C-bus interface with 30 mA high drive capability on SDA output for driving high capacitive buses
  3. 4096-step (12-bit) linear programmable brightness per LED output varying from fully off (default) to maximum brightness
  4. LED output frequency (all LEDs) typically varies from 40 Hz to 1000 Hz (Default of 1Eh in PRE_SCALE register results in a 200 Hz refresh rate with oscillator clock of 25 MHz.)
  5. Sixteen totem pole outputs (sink 25 mA and source 10 mA at 5 V) with software programmable open-drain LED outputs selection (default at totem pole). No input function.
  6. Output state change programmable on the Acknowledge or the STOP Command to update outputs byte-by-byte or all at the same time (default to 'Change on STOP').
  7. Active LOW Output Enable (OE) input pin. LEDn outputs programmable to logic 1, logic 0 (default at power-up) or 'high-impedance' when OE is HIGH.
  8. 6 hardware address pins allow 62 PCA9685 devices to be connected to the same I2C-bus
  9. Toggling OE allows for hardware LED blinking

 

 

Production Version

Finally here is the version of this system we are producing, 64 channels of light control, with a camera trigger, and all controled off an SBC based around the MBED controler board.

So the solution splits nicely into three sections, a control system, with the external Input output (Network, and RS232), plus two I2C channels for the internal cards, a card to control the light levels of the attached LED's, and a general 8 channel relay output card to trigger the camera, and other attached devices under computer control.

Here there is a copy of the test code to drive the dome built on the MBED compiler in March 2010, describing the what each part does and the simple scripting language it give the user.

LED's Used by the Dome

Vio High-Brightness LEDs provide all the benefits of solid-state lighting - energy savings, long life, robustness - and do something many white LEDs do not ... create exceptional light quality. Vio combines 405 nm violet chips with proprietary phosphors to create a natural white light that meets the high standards of lighting professionals. Vio features minimal part-to-part colour variation with a colour shift of less than 75 Kelvin over a 50,000-hour rated life. The result is a stable, more uniform warm white light, similar to a soft white incandescent lamp, that enables lighting designers to create a look that lasts.

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