Lightbox Project

For museum-quality fading effects, consider plugging an Infineon LED ShieldInfineon LED Shield on top of the Arduino. The Shield can be used for three channels of lights, but you could just use one channel, or connect all three to white lights. Probably you want individual LED modules, so you can space them accordingly, and positioned about 10 cm back from your translucent panel (anyway this is just a guess, you may need to experiment). You can send I2C commands from the Arduino to the LED Shield to control brightness, fading etc. You didn't give enough information, perhaps through-hole LEDs like these through-hole LEDs like these are easily solderable to a stripboard to be mounted in your box .About 12 of these (all soldered in series) per channel would work, so a total of 36 of them driven from a single Shield, powered from a 48V DC supply.

For wireless control I don't know of anything specifically for the Arduino that is easy to use - perhaps others have suggestions.

EDIT: See: RGB LED Shield from Infineon - Getting Started Guide the first bit shows how to get a basic program running with the Arduino and the LED Shield, there is an I2C setting that controls how much current is driven through the LEDs, it would need setting to suit your particular LEDs (see 'Adjusting the Desired Current' section there).

Thanks so much for your reply!  Was planning to use LED strip lights like these Amazon.com: eTopxizu 32.8Ft /10M DC 12V Flexible 5050 RGB LED Strip Light With 44key LED Controller and 12V5A Power Adap…  Positioned on the back panel of the lightbox 2-3" from the transparency.  I was thinking of using the arduino to program microprocessors because aesthetically I do not want to run wire to all boxes from a single arduino.  I am not sure if the AtTiny microprocessors can handle the voltage of the LED strips (and not sure how to figure that out exactly).  The LED strip would plug into the wall with an AC/DC adapter.  These lights do have remote control IR sensor...perhaps that could be hacked to control wirelessly from IR motion sensor??

The shield sounds great but have 4-6 boxes so cost would be too much at $22 each and an arduino for each box.  If I could find a way to rig it up cleanly, I could do two shields and two Unos for 4-6 boxes.  Just don't want to wire all the boxes together. 

Here is the wireless motion sensor plan I found: Cheap Wireless Motion Sensor Device

Basic idea: Hack your LED Strip with a Motion Sensor and Timer

AtTiny fade code I found (but no idea how smooth or good it is) https://codebender.cc/sketch:62995

Example of Lightboxes using RF controlled wall outlet and motion sensor, from SmartHome but expensive for multiple boxes and not sure how to integrate the fade effect etc: https://www.youtube.com/watch?v=ZNk6Pp0OKjM 

Also found Fadecandy which is controlled over usb but no idea how many strips it could control or wireless capacity: https://www.adafruit.com/products/1689

Know there must be a relatively simple solution to this but could be fooling myself....  Hope I can make it work!  I could live with a full on brightness at motion detection and slow fade out if that simplifies things...

Thanks again!  I really appreciate the advice!

Leslie

Hi Leslie,

To perform fading you ideally need some way of achieving PWM. You mentioned white light in the original post, but those LED strips that you referenced are color ones (RGB), and when you use them for white light, you only get 255 brightness levels, so you can see it visibly fading in steps. The fadecandy thing may resolve that to an extent but I don't know. Otherwise, you need something to perform PWM and white LEDs.

You could use white LED strips but they are not controlled in the same way as the RGB ones that you found. The LED shield can be used to control the strips, but ideally the shield is designed for LEDs in series without resistors, but strips are designed with parallel LEDs with resistors. It will function, but not as well.

EDIT: Regarding your comment about instant-on and just fading off, if you're prepared to have not much control over it, you could just experiment with a capacitor across your supply to the LEDs. When the power is disconnected then the LEDs will fade off. Then you don't need PWM nor an Arduino. Really not ideal, the effect may not be acceptable, but other solutions will cost more (e.g. PWM).

The capacitor sounds very simple and appealing at this point!  I feel way out of my depth and in need of further training in programming and electrics. Given the time limits I think it's best to keep it as simple as possible.

A slow fade down would be great!  Know about how slow the fade would be approximately?  Type of capacitor? 

To make sure I am thinking about this correctly:  The LEDs would be connected to a capacitor attached to a motion sensor, correct?

Would this white LED strip work better: http://www.amazon.com/dp/B01339G2F6?psc=1

Thanks!!!!!

Leslie

When your talking about fading in and out, over what time period ?, with 2 minutes of on time (Subject to no more motion), are we alking about just a few seconds to fade up and down, if so then you may be able to do it without a micro at all, if the motion sensor is very close to the light panel..

either way you will need some wire to each panel to deliver the power to the LEDs and to the control system

could you sketch a picture of the desired layout ?

Thanks

Peter

Hi Leslie,

You might want to go to the Cypress Semiconductor PSOC 4 board.

They are about 4 USD each and can control I2C LED's through the Infineon shield.

The Cypress boats also support capacitive sensing.  Basically you can tell when someone is within a few feet of your box to turn on the LEDs.

The Cypress development environment might look intimidating, but it is really simple to learn and very powerful.

DAB