Archive for February, 2008

The Incredible Shrinking Capacitor

Wednesday, February 27th, 2008

Projector Repair

I had always heard that when a piece of electronic equipment fails, the electrolytic capacitors are often a prime suspect. I got a much better sense of that today as I tried my hand at fixing an old digital projector I had gotten from a friend.

The unit wouldn’t even power on and while I suspected the power supply, I wasn’t able to figure out why it wasn’t working. That is, until I went online and found a post on Fixya.com where other people had run into a similar issue. One poster pointed out that there are four aluminum electrolytic capacitors on the power supply board which are rated at 85 degreesC and, because the board gets so hot in normal operation, these are often the first to fail.

I found the capacitors and they looked ok; their tops weren’t bulged nor did I find a short circuit across their terminals. I needed a way to test their capacitance (since I don’t have a multimeter with this function) and so I set up your typical 555 timer circuit where you use an unknown capacitor with two known resistors and you calculate the capacitance from the resultant frequency. When I did this, sure enough, I found the capacitors in question were significantly below their rated capacitance values and were in need of replacement.

One capacitor in particular, a little 100uF one, was particularly strange in the fact that it’s capacitance changed dramatically while I was watching it on the oscilloscope. I watched it start from around 40uF (still too small) and dwindle down to mere picofarads in the span of a minute or two. I thought it was so neat that I captured a video of it.

(a definition of the word “neat” you weren’t previously aware of, I bet)

I later found out that the whole shrinking thing was a function of it having being heated by the soldering iron and cooling down. Still, I thought it was cool.

Anyways, I replaced the capacitors and plugged the projector in and…. nope, still doesn’t work. However, the fans *do* spin up which is way more life than it had previously and also I’m seeing some stable voltages on the power supply for once. Looks like there’s some other issue at work as well.

Building an Electromagnet pt1

Sunday, February 24th, 2008

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My friend Phil has recently been toying around with ferrofluid (a unique type of magnetically reactive liquid) and with the idea of using computer-controlled electromagnets to make them dance. I like this idea and have been building an electromagnet that I hope will be stronger and give us a better response than the magnets we’ve built so far.

Using some mild-steel rod donated by Hazard Factory, I spent some time last week on the lathe working it into the electromagnet casing pictured above.

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LED Par Can Take-apart

Thursday, February 21st, 2008

COLORSplash Jr.Burned out LEDs

Today I received in the mail a Chauvet COLORsplash Jr. LED Par light. This is basically a spotlight that you can control the color of with a computer using the DMX protocol. I thought it’d be handy to have a general purpose color-controlled light for when I need to get an idea of how a certain effect might look.

The place I bought it from had it listed as a ‘scratch and dent’ item and was selling it as a discount with the guarantee that the unit would work flawlessly. Unfortunately upon turning it on I found that three of the green LED’s were dark.

Giving the unit a couple of taps, I was able to get the three dark LED’s to flash on momentarily suggesting, ah ha!, a simple loose connection. Expecting a quick repair (and hoping to save myself the hassle of returning it) I took the unit apart and traced down the problem.

COLORsplash Jr. taken apart

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Molten Metal LED Display pt2

Wednesday, February 20th, 2008

As promised, here’s some video of my recent fun with Wood’s Metal. Thanks to Phil for recording this.

Some basic stats:
LEDs: 54
Resistors: 40

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Say it with Solid State Lighting

Thursday, February 14th, 2008

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I knew that those LED strip lights that I got would come in handy.

I had more planned for this display but unfortunately Kayobi came home earlier than expected and cut the preparations short. Oh well!

Serial LED Strip pt1

Wednesday, February 13th, 2008

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This is a simple snapshot glimpse of something I’ve been working on: a serial LED strip light. Basically instead of all the LED’s being lit at once, there are shift registers which drive the LED’s as part of a big daisy chain.

There are two primary goals for this:

1. make every LED be addressable by driving the serial clock *really* fast

2. drive the clock slower and turn the whole chain into a sort of “light pipe”.. where you turn a LED on at the start and you see it animate down the chain. I have a couple ideas which use such a display.

Besides, circuit layouts look pretty.

Molten Metal LED Display pt1

Sunday, February 10th, 2008

A week or so ago I picked up a modest quantity of Wood’s Metal, a low melting-point alloy which melts around 158 degrees F. I’ve been playing with the idea of using it as a dynamic circuit element in a display of some sort.

On saturday I built a LED array with pins that extended through the bottom of the circuit board as a proof of concept. The idea being that the LED’s would all be wired up with their cathodes tied to ground above the board and their anodes extending as naked pins beneath the board. Power would also be wired as separate naked pins beneath the board. Liquid metal could then be flowed underneath the board, randomly connecting and disconnecting the LED’s from power, turning them on and off as the metal flows by.

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Shipment of new LEDs

Friday, February 8th, 2008

A friend of mine who I’ve been working with found a good deal on LED’s from a Chinese supplier and put in a bulk order. I went in on it and my share of the stuff arrived today!

I got a few hundred RGB SMD LED’s along with some very interesting RGB strip lighting. I also picked up a few DMX controllers for good measure.

DMX LED ControllerNew SMD RGB LEDs and RGB Strip

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How not to make a Faraday cage

Wednesday, February 6th, 2008

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Today a thought floated around in my head of those little mesh screens they put on the door of microwave ovens. The holes in the screen are spaced smaller than the wavelength of the microwaves and that’s why it makes an effective shield. At least that’s how I understand it.

Then I thought of all the 60 Hz electromagnetic interference I’ve noticed on my oscilloscope while tinkering around in the lab. The two thoughts collided and I was wondering, hey, the wavelength on 60 Hz is something around 5,000 km, huge. So does that mean if I surround something with, say, just a wireframe cube of wire which is somewhat smaller than 5,000 km, would that be enough to shield it from interference?

Only one way to find out!

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