(Note: these photos were taken not by me but by my friend David Lindes, who has a ton of other amazing photos on Flickr)
It’s 3 a.m. and a phone rings in the White House…
Or actually, it was about 3 p.m. and a phone rang in my pocket. By luck the phone happened to be mine and on the other end of it was 3ric asking if I’d be able to help with a project that evening. Seems he had acquired about 10 liters of liquid nitrogen and among other things was hoping to use it to do some high-speed flash photography of frozen things shattering into a million pieces upon being shot with a pellet rifle.
All was well and good and according to plan, except for the flash trigger, which was stuck in the mail somewhere. Could I hack one together by evening? Thus is how I got my project for the day.
A flash trigger for high-speed photography is a really simple device. Basically all you need to do is take an audio signal and use that to trigger a flash if the signal exceeds a certain level. Rather than muck about with $10 worth of op-amps, transistors, voltage dividers and a bunch of so-called “electrical engineering”, I splurged for the $2 solution and threw the equivalent of a mid-1980’s personal computer at the problem… i.e. a microcontroller. Specifically, a AVR ATMega168 (mounted on a $30 Arduino).
Long story short and after overcoming two rather significant obstacles (#1 being not having a microphone, #2 being not having a flash) we were able to kludge together a workable flash trigger in just a couple hours. With the flash trigger in place and David at the camera, by the end of the evening we had walked away with some decent shots.
It truly astounds me sometimes how much work can go into a PCB layout, even a relatively simple one. I’ve spent a better part of this week refining the design of the serial LED striplights I’ve been working on. I believe they’re just about ready to be sent off to a board house for a prototype run. Infinite thanks to Dan for helping to catch my gotchas before they became design show-stoppers.
Note the bendy circuit traces and teardropped holes. These are apparently things you have to do when you’re designing with flexible circuits in mind.
Today while cleaning up the lab I came across a little blue ball lamp thing which was my first ever LED project some many years ago. I had found the little guy at a garage sale and later swapped out the incandescent light bulb inside of him with a small array of 22 blue super-bright LED’s.
Not really knowing any better at the time, I had wired all 22 LED’s up in parallel with each other, all of them “sharing” one resistor. Ah how naive. No wonder the lamp got progressively dimmer and dimmer over the years as the LED’s fought each other over current, seeing which of them could burn itself out first.
For fun and nostalgia today I decided to revisit my little blue ball lamp and do it proper (or at least more proper). I yanked out the (now half-dead) 22-LED array and replaced it with a 5-watt blue power-LED.
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.
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.
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.