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A Giant DIY LED Display
smf28 writes "Dheera Venkatraman has created a giant DIY LED display featuring 36 blue Luxeons in a 6x6 array on the windows of Simmons Hall, an undergraduate dormitory at MIT famous (or infamous, if you wish) for its design. Recent uses included welcoming students in September, Pirate Day, and others."
Looks like a project out of the book Hardware Hacking Projects for Geeks.
Nothing to see here, move along.
I'd much rather they not corrupt the project by doing that. It's awesome as is, if it turned into yet another kind of lame advertising, that'd suck.
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Being a crontrols system desiger, I hope some of the goofs of industry look at stuff like this. I am constantly yelling at my vendors that I don't need a super screwed up version of RS232/485/422 etc to network sensors around a machine......binary and ASCII protocols WORK GREAT for stuff like this. KISS (Keep it Simple and Stupid). A few micros some twisted pairs and your basic switcher......bingo big network of fun.....if you need some more bandwidth, throw Ethernet at it. I've been saying this for over 10 years and still all the big players want to sell you a "Field Bus". I hope some of the MIT guys move in with the big guys...and slap some sense into them.....rant off.
The microcontroller should have a separate supply, and as the consumption of the PIC is so low this could be derived simply by passing the LED supply through a small low voltage drop diode (Schottky diode) and preferably a suitable inductor, and then decoupling it with electrolytic and ceramic capacitors (say 1000uF and 100nF) in parallel as close to the Vcc pin as possible. With this arrangement, the LED Vcc can even momentarily drop to zero and the microcontroller will just keep running.
(In fact, if you are thinking of doing this from scratch, you do not need an expensive supply at all. Rectify the output of a transformer directly to provide pulsating DC (100Hz Europe, 120Hz US.) This is the LED bus. You can do that with a 35A 50V bridge rectifier bolted to a nice big alumin(i)um strip. Then pass the output through a diode, a suitable resistor, and stabilise it with a 5.1V Zener. Assuming a peak of about 8V from your transformer, a 1A Schottky, a 10 ohm 3W wirewound resistor and a 5W 5.1V Zener will do just fine, with maybe a 1000uF electrolytic and a 100nF ceramic to stabilise the voltage at the PIC and provide enough surge capacity to drive the MOSFET gates. That way, you avoid the major disadvantage of switching power supplies, which is that they do not like rapidly varying loads.
Oh, another thing. Do not put a resistor between the PIC and the MOSFET gate. Use a driver chip to translate the current levels. Cheap insurance.
Pining for the fjords
Sorry, I dont see why this is a story. The technical difficulty of this is something like "my first microcontroller project" from "toying with electronics 101". The implementation is not even that interesting. (Multiplexing anyone?). The novelty is almost zero (giant LED display.. uhhh). Yes, it is at this geek university, but that is the only real point about this story i can see.