Monthly Archives: January 2010

[Photography] – w00t! Image sale!

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w00t!

Some guy in France just licensed one of my images for a post card!

In case anyone is wondering, he’s doing a small run of 250 post cards. I licensed the image – which had already sold 2 copies at an art show – for $0.10 per use. My art’s audience are impulse-buyers, and in this economy discretionary spendings is quite low. For the profit margin that a post card can generate, $0.10 per post card seems reasonable. Now I can say I’m a published photographer. (Hah).

Besides, the image had already been released into creative commons under BY-CC-ND anyway, so it has, IMHO, little commercial value. And it was really cool that he asked, instead of ripping the image off on Flickr.

Here’s the image in question:

Space Needle and Pacific Science Center

It’s already the screen background for some local Mac developer :-)

[Fail] – Toner transfer for “photo”-etch

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Well, no project always go 100% smoothly, and the important thing when one fails, is to document the failure.

Tried to use a toner-transfer method to do a photo-resist mask tonight, to chem-etch a brass face plate for a couple of pieces of photography that I’m framing up for presentation / sales. I’ve done this before in college doing DIY PCBs and earlier on in high school for model airplanes.

The process involves mirror-inverting a photo negative of the mask pattern and then printing it out on a photocopier. Because toner is a thermoplastic, a regular clothes iron can be used to remelt the toner and transfer it to another medium – balsa wood for cutting (this is before laser cutters) or, in my case, a sheet of brass plate from K&S Engineering in Chicago for a name plate.

Turns out I forgot that you need special paper. Toner sticks really well to regular paper (no surprise):

Blogged: http://www.TerenceTam.com

Oh, and it helps to turn the steam off on the clothes iron. :-)

I think this is the stuff that I used in college. I’m placing an order tomorrow for a small sample, shipped pony express (ground) from Florida. So, check back in a week to see how it went.

[Engineering] – More bullet sensor validation testing

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Tonight, I did more engineering validation testing of the IR breakbeam sensor mentioned in the previous article.

First, the setup. The sensor is securely mounted in my benchtop vise, with a phone book propped up behind the bullet path as a pellet trap. (Finally, a good use for those dead-tree edition phone books!). A regulated DC power supply is used to provide the power to the sensor module, and my oscilloscope is used to monitor the signal line. As before, we set the oscilloscope to trigger on a falling edge signal at a level close to DC Bus -.

Blogged at: http://www.TerenceTam.com
Blogged at: http://www.TerenceTam.com

(I need to get my garage sale O-Scope probes checked. They don’t seem to be reading the voltage right, but at least the signal generator test indicates a good test pattern. Probably something stupid I forgot to set in the software. I’m still learning how to use this thing).

Next, I set the oscilloscopes time scale to 100 nanoseconds per division. Yup, definitely picking something up! That’s a good sign. Rechecking at 1 microsecond per division shows a fairly clean signal.

Blogged at: http://www.TerenceTam.com
Blogged at: http://www.TerenceTam.com

To give Dad a good idea of what he’s engineering to, I need to take some measurements of the pulse width of the event. We’ve previously calculated about 18.3 microseconds for a round ball at 1000fps. (Note that we actually don’t know how fast the air rifle is shooting at, nor is the pellet perfectly round.)

Blogged at: http://www.TerenceTam.com

Look at that! 20 microseconds. Love it when the calculations matches real life data.

Blogged at: http://www.TerenceTam.com

The next shot clocked in at a mere 5 microsecond pulse. There could be 2 reasons: A) the angle of the flight path through the sensor might be changing, or I might be nicking the beam differently. Still, the oscilloscope clearly captures a 5ms pulse.

Blogged at: http://www.TerenceTam.com

Another shot, this time generating a 10ms pulse.

Blogged at: http://www.TerenceTam.com

Yet another 5ms pulse again – followed by a lot of electrical noise. That’s strange…

Blogged at: http://www.TerenceTam.com

Looks like the round nicked the sensor housing. Yeah, that would explain the sensor noise.

Remarkably the sensor still works. Putting the gun aside, I grabbed the soldering iron sponge and started dripping water past the IR beam. It registers on the O-Scope! (translation – this can be used for those awesome water-drop shots!)

Finally, here’s a couple of pellets recovered from the phone book. Love how you can see the rifling marks on the pellets :-) .

Blogged at: http://www.TerenceTam.com

[Pranks] – Difference between a cool job, and an AWESOME job

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You know what the difference between a cool job and an awesome job?

When you have a bunch of coworkers that relies on wit to prank each other. Better yet, when you can prank your boss, and he appreciates it.

Jared, the other Mechanical Engineer at my day job, also has a side business, building parts to soup up Evos. (Peeps, go over to his website, Binary Engineering, and give him some web love). Recently, to advertise his car, and his mad engineering skillz, Jared got a vinyl plotter.

Used to be that if you wanted a vinyl plotter, you were stuck with a Roland or Summa. These are the 800 lb gorillas in the vinyl plotter world – expensive, well crafted machines.

But if you think about it, a vinyl plotter is just an X-Y plotter with the ability to lift and lower a swiveling tungsten carbide blade. And the stepper motors and drivers required to drive such a system had come down drastically in price lately.

Enter the joys of Chinese manufacturing, stage left. Now, for < $400, one can buy a 24" wide vinyl plotter. The software's not as refined, and the cutter is a loud, cheap, affair - but it gets the job done.

And of course, what do creative engineers do given a new toy? They find a way to prank someone.

Here's a caricature of myself I found at my desk when I came in Monday morning:

IMG_9154

And here’s a new door decoration for my boss. He owns a Harley, so we have a feeling that this one’s gonna be up on his door for a while :-)

IMG_9158

:-)

[Engineering] – Testing of a Break Beam sensor

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Today, I performed validation testing of the breakbeam module selected to handle bullet-detection for high speed photography. The sensor module is a Sharp GP1A57HRJ00F from SparkFun Electronics (Datasheet). This is an infra-red emitter / detector combo: one half of the module holds an IR LED, the other half an opto-transistor detecting the output.

The output on Pin 2 is at TTL High until the beam is broken, then it goes to TTL low.

I wanted to make sure the sensor does as advertised (remember, I’m a mechanical engineer by trade, that happens to dabble in electronics and coding). So I hook it up with a breakout board and populated the current limiting resistor with a SMT 231 ohm resistor that we’ve got lying around the lab. Here’s the schematic:

001

Connecting Vcc to a 5V DC power supply in the lab, and connecting a probe from an oscilloscope between SIG and GND, I was able to get the following response:

TEK0000

As you can see, the output on the signal switches rather quickly. The oscilloscope was set to trigger off the falling edge of the signal at approximately 3.8V and the drop in voltage occurred within 20 *nano* seconds.

If we assume a .22 round that’s spherical in shape (say, a BB), travelling at 1000 fps:

Each milli-second the round covers 1 ft
To cover .22, or 0.0183ft, the round will take 0.0183 millisecond, or 18.3 microseconds.

I’m fairly confident that the round firing through the beam can trigger an electronic response. The next challenge is then designing electronic circuit to lengthen this response to a switched pulse to fire a pocket wizard radio transmitter.