Custom light sequencer

1 December 2008

Having already built several projects requiring a 12Vdc sequencer, such as my Prototype lamp

prototype2_01_500

and my Conduit sculpture

I realized that experimenting with new projects with similar lights would be easier with a common development platform . . .

As part of a larger project supported by an artist grant from the Ontario Arts Council, I was able to build a prototype light sequencer, based on a PIC 16F877 microprocessor and two custom solid-state-relay output boards:

circuit_boards_01

The PIC model was chosen based on its native I/O capabilities (16 digital outputs and several digital and analog inputs), and the solid-state-relays were chosen based on their high current carrying capability and low on-resistance, resulting in a negligible voltage drop across the relay (I couldn’t find an ideal transistor with a consistently low voltage drop when switching different load types such as cold cathode tube ballasts vs. EL wire ballasts, and was thus dissatisfied with the amount of voltage I was losing just to the transistor when switched on).

The PIC controls the output relays to directly switch the power from an external power supply to the loads (lights, motors, etc.); the advantage of this arrangement is that the output voltage and total available power of the sequencer is governed by this power supply which can be easily substituted based on the voltage and current requirements of a particular project.

The modular design of the system — main processor board and separate relay boards — allows me to mount the sequencer on the back of fixtures

candela_2008_01_

or house it in its own enclosure:

seq_16_inside_500

The control board also has screw terminals for attaching input modules, such as this prototype proximity sensor based on a Sharp IR sensor:

Having a modular, easy-to-connect framework for the controller, sensor modules, and lights allows me to quickly experiment with various interactive arrangements, and has lead to several site-specific, interactive lighting installations.

Below are a few sample videos of some temporary installations built with the system. These installations used several motion sensors to control the light colour based on the direction or location of people in the exhibition space, while controlling the speed of the sequence based on the number of people passing through the space; the installations’ behaviour were thereby a reflection of the human activity within the space.

Future plans for the sequencer include migrating from a PIC processor to an Arduino (simply by changing the processor board), making more input modules, and creating a wireless network between the input and output modules.

More info can be found here.

Comments (6) | Tags: , , , , , , | More: Blog

6 Responses to “Custom light sequencer”

  1. TS says:

    I am curious about your transition from a PIC processor to Aruino. I am looking at some similar projects, interactive light sequencing hardware. It seems the PIC processors are much cheaper @ $4, versus $30 for the Arduino’s, but that the Aruino’s are more self-contained/easier to use devices. I am intersted in what works, and what doesn’t, and what is worth learning.

    Thanks for your Blog,
    TS O’Grady

  2. ao says:

    TS,

    Hi, thanks for checking out my blog!

    The Arduino is based on the ATmega328 chip by Atmel which is actually comparable to PICs in price. The $30 Arduino board is more of a development board; for my final projects I don’t embed a whole Arduino board, but rather just an ATmega328 chip, just as I would w/ a PIC. The advantages of working w/ the Arduino environment are all the easy/accessible support and libraries for various sensors, displays, etc. The limitation is that an Arduino can only do so much, but so far people have been stretching its capabilities pretty far. If you are new to microprocessors, I’d def. suggest starting w/ Arduino.

    Cheers,
    ao.

  3. TS says:

    Thanks, I think you have answered my 2nd question too. I am looking at either the Arduino Uno or the bigger more expensive Mega. I will be wanting to dim 6 channels of lights, so I think I may have to step up to the Mega and its higher price.

    What kind of limitations have you all run into, and will the Mega alleviate them?

    And thanks for explaining how you pop out the Amtel chip for final projects. Yes, that makes Arduino the way to go.

  4. ao says:

    No worries . . . Limitations w/ the regular Arduino can be RAM and program space, which can *sometimes* be fixed with clever programming; though this totally depends how complex your application is. I/O pins can be a limitation, though these can often be solved with shift registers, mux’s, or the like.

    Since the mega uses a surface mount chip, it won’t be as straightforward to integrate that chip into your designs independent of the board, and the Mega board is certainly more expensive than the Uno.

    For another option, in between, look up the Sanguino.

    All that said, I wouldn’t be too quick to jump from the Uno right away: depending on what you will be using t0 dim the light loads, you may have enough I/O already — I believe it has 6 PWM capable pins, and I believe there are libraries to create more as well — or if you are using a driver chip or other peripheral, you may only need to use the serial port, SPI, or I2C which would only need a few pins.

    That’s about all I can offer for now based on what I understand of your application.

    Good luck and have fun,
    ao.

  5. TS says:

    So I just ordered a clone Mega 1280 for $30 from a US seller on EBay. Not as good as the new Mega 2560, but I think 128k is plenty of memory. I want to avoid having to be clever in programing to avoid the memory limitations. Yeah, it is a surface mount chip, but I think it will be a nice environment to learn in. Later I can move to a DIP chip.

    Speaking of learning, what did you find useful as resources to learn the ins and outs of interactive light control with the Arduino? ? ? ?

    I will be doing a lot of reading before my Mega gets here. I am downloading the editor/compiler now.

    Yes I hope this will be fun.
    thanks again,
    TS

  6. ao says:

    Good luck w/ the Mega clone. I’d say the best resources are at the Arduino site: the Playground and the Forum.

    Looking forward to seeing what you come up with, cheers,
    ao.

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