Wednesday, March 17, 2010

Electronics Update

My task for the last two weeks has been to figure out how to build the interactive lighting system for the wall. We want to be able to light each segment of the wall independently so that the wall will react as people walk by it.

To detect the people we are using ultrasonic proximity sensors spaced every two feet along the wall to create a series of zones that we can use to detect where people are in front of the wall. We are using the maxbotics lv-ez3 sensors which have about a 2 foot beam width. If a single sensor detects a object than it means some one is standing directly in front of it. If two adjacent sensors both detects an object, it means that someone is standing between 2 sensors. Multiple people standing in front of the wall will create some from very dynamic patterns.

The LED are going to be mounted on a strip along either the top or bottom of the wall. It's cheaper to use a separate led for each color instead of using a RGB led like we were experimenting with before. This is a very common method used in professional led stage lighting. We will have a cluster of 4 leds: a red, green, blue and white placed every 6 inches. They will be controlled in pairs so we can have different qualities of light (color, brightness) every foot along the wall.

High powered leds are very expensive from US suppliers but they tend to be brighter, more energy efficient and last longer. For us poor college students, we need a cheaper solution. The Chinese are very good at making cheaper versions of everything, and guess what? They make LED's too. They may not be as good but for the price difference, they will be good enough. I ordered 64 High powered 3Watt LED's from a Chinese company I discovered looking on eBay. The LED's are currently on their journey to the US. It takes about 2 weeks for things to arrive via cheap post.

To power the LEDs I need 32 led Drivers - one for each color in each 1 foot segment. I liked the ones I had bought for our led demo lamp so I ordered 32 more. However they are currently backordered about 3 weeks. The company said they would be able to get them to me by the middle of April when I must have them for assembly. They offered to send me some of their older model, but they aren't nearly as energy efficient (they lack a voltage step down chip and use resistors instead). I've looked around and haven't found anything I think will work better. The led driver is really only 4 parts so we might be able to build them ourselves....

To control the drivers, I need even more chips. The drivers have a sense input that can read pwm output from an Ardiuno. The problem is that the Arduino only has 6 pwm outputs and the mega has 14; not nearly enough for 32 channels I need. The solution is to use a chip that can interface with the arduino that has more pwm output. The best documented chip for this is the tlc5940. It takes serial input and has 16 channels of pwm output and you can daisy chain 10+ chips for all of your pwm needs. There is great arduino library written for them that makes using them almost painless. they come in DIP form so you can use them on breadboard. I have two on order and they should be here next week!

Next step is getting stuff wired together.
This week I plan on soldering wires on all of the proximity sensors and getting them tested. there are some issues that may arise with them picking up each others sound pulses but it can alternating back and forth which ones are pulsing.

Once the tlc chips arrive I plan on doing a small scale test using small rgb leds on breadboard and getting the code sorted out so I don't have to worry about it later when the led drivers finally arrive.

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