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April 14, 2010

Wireless Power Transmission, Part V [Project]

A big gap

Sunday was a big day! Jamison and I started with another trip to Fry’s. We needed more magnet wire, a better power supply to clean up the noise we saw on the cheap one we already had, and some perfboard. On the way home, we stopped by Home Depot for 6″ pipe and Fred Meyer’s for reading glasses. Never needed those before… 8-)

Upon our return home, we set up our lab and pulled out the new power supply. After deciding to use a different scope probe and calibrating it (we missed that step last time), we got a nice, clean 5V voltage. Because we wanted to see the contrast, we then connected the probe to the cheap “wall wart” power supply. Look at that — a nice, clean 5V voltage! Huh. I guess the new power supply can go back and I’ll try to be more understanding when a customer calls for tool assistance and hasn’t calibrated his scope probes.

Jamison wrapped a second coil and we hooked it up to a green LED. Connect the power, move the coils close together. First light! Yes!!

Now it was time to improve Jamison’s project. We tried a full-wave rectifier to increase the LED’s brightness, with not a large (if any) effect. We built a two-stage Cockcroft-Walton generator, with much better success.

Next we decided to improve the coils. We cut the 6″ pipe into short lengths, an inch and a half or so. We wrapped the magnet wire around them and used the oscilloscope to tune the number of wraps to get the desired frequency. It seemed like we were having to remove too many coils, so we found a formula for the inductance of a short air-core cylindrical coil. Plotting inductance as a function of wraps showed we could get by with much fewer than the 18 wraps we thought we needed for the desired 53 uH.

Emboldened with new information, we continued experimenting and found twelve wraps got us nearest to the desired 80 kHz frequency. We built a second, matching coil and we found we could transfer power much farther. The first set of coils had to be nearly touching. The second set could be more than four inches apart.

Unfortunately, we hadn’t left long enough leads on the coils, so we decided to wrap another set using all the information gained along the way. The forms were only an inch “long.” We sawed deeper groves for the wire’s start and end so the coils wouldn’t need to spread and we spaced tape around the coil to hold them tight. I haven’t measured, but I think we can have six inches between the coils and still light the LED.

We want to try making a smaller secondary coil, maybe an inch in diameter. That will be for another day.

But wait — there’s more

See all posts on the Wireless Power Transmission project.

Jamison’s project is based on the Instructable, “Low-Power Wireless Charging.”
April 13, 2010

Wireless Power Transmission, Part IV [Project]

Oscillator

A couple of weeks ago, we last documented Jamison’s progress on his engineering project. Much has happened since then.

Decide on prototype

We thought we’d decided what project to build (I thought we were building Wireless Electricity), but Jamison changed his mind. After further research, he decided to build the Low-Power Wireless Charging he’d found on Instructables.com. I’m pleased. We’ll have more control over this project.

Buy materials for prototype

Once we knew what project to build, we thought it would be easy to buy the parts. Wrong!

Buying capacitors is a confusing process. The units are insane. The instructable specified a 100 nF capacitor. That sounds easy enough. Unfortunately, Fry’s shelf labels would list it as a 100000 pF or a .10 MFD. That’s if they actually had it. After trying to find the right caps, we decided to do our shopping online instead, and headed over to digikey.com. We had all the parts we needed the next day. :-)

Build prototype

Prototype building went well, at least for the circuit. Once Jamison understood how the little holes in the breadboard are connected, the oscillator went together fairly quickly.

The first coil went together fast, too. The instructable said to do 18 wraps of 15 cm loops. Jamison wrapped the coil on a form, about 4.5 inches square, and then rounded the coil by hand.

Tune coil

Tuning the coil was a problem. The oscillator was designed for 80 kHz. We should have been able to tune the coil by connecting it to the oscillator and removing coils until the oscilloscope showed something near 80 kHz. Famous last words. Instead of a nice sinusoidal signal, we got a noisy, stepped signal. Removing coils didn’t seem to do anything. Maybe the coils were separating, so we wrapped it in electrical tape. That made no noticeable change. Maybe the cheap power supply was causing the noise. Fry’s could rescue us with a nice benchtop power supply.

Time to call it quits and figure out our next step.

But wait — there’s more

See all posts on the Wireless Power Transmission project.

Jamison’s project is based on the Instructable, “Low-Power Wireless Charging.”
April 9, 2010 2 Comments

Social Media Interaction

I asked a question on social media:

  1. As a tweet: Experimenting with a “spoiler” class for CSS. Does this work for iPad users? http://blogan.net/blog/2010/04/05/gone-tomorrow-book-review/
  2. As an @reply on Twitter: @jabancroft Does the “spoiler” CSS work for you on your iPad? http://blogan.net/blog/2010/04/05/gone-tomorrow-book-review/
  3. As a Buzz post: I’m experimenting with a “spoiler” class to hide content in a blog post until the reader clicks on it. I had originally thought of doing a “mousever” even, but was sure this would block iPad readers. So, all you iPad owners out there; does this work for you? Here’s a blog post that uses it: http://blogan.net/blog/2010/04/05/gone-tomorrow-book-review/
  4. As a Facebook status: Any iPad users out there? If so, please go to this blog post of mine and let me know if the “spoiler” class works for you. In other words, can you read the blacked out text if you “click” on it? (Those of you on older browsers, you’re probably out of luck…)

The questions aren’t identical, but that’s largely because of the various social sites’ constraints: Facebook and Buzz allow for longer posts than Twitter.

Results:

  1. The tweet got a single response, but in reality it was a response to a later tweet of mine. Regardless, it didn’t answer my question. That’s with 485 followers.
  2. The @reply got a response and it answered the question. Thanks, Josh!
  3. The buzz post sits quiet. This seems to be a trend on Buzz. No one gets interaction unless they have a ton of followers. I have only 64.
  4. The Facebook status got two responses, both helpful. I have 322 Facebook friends.

I get much better interaction on Facebook than anywhere else. I think it’s because I’ve limited my Facebook friends to people I actually know.

What about you? Where do you get the best interaction?

April 5, 2010

Gone Tomorrow [Book Review]

ISBN is 0440243688 Every once in a while, I read an action-mystery novel. Then I’m reminded why I don’t read them much anymore. Lee Child’s Gone Tomorrow: A Reacher Novel is my latest reminder. I bought it the afternoon of April 4 while waiting for a flight home; I finished it later that evening (or maybe about 15 minutes into the next day).

Gone Tomorrow follows Child’s typical formula: Jack Reacher, while minding his own business, gets sucked into a situation requiring his unique abilities: telling time without a watch, owning only one set of clothing which he never launders, rarely bathing, and apparently never using deodorant. You might think I’m being unfair but I disagree — Reacher’s clothing and hygiene habits are so important that Child’s books document Reacher’s every clothing purchase and shower.

Reacher possesses nearly superhuman powers of observation, analysis, and combat.  Taking on entire teams of baddies singlehandedly is Reacher’s M.O. Of course, Reacher is not the only prime specimen in Child’s books; his villains and helpful cohorts tend to include young, attractive and fit females (yeah, some are even attracted to Reacher, go figure…) and Gone Tomorrow is no exception.

Even if you can overlook Reacher’s idiosyncrasies and exaggerated capabilities, you’ll have to endure a plot where, [Spoiler alert. Click to read.] at the climax, the villain throws down her gun, choosing instead to fight Reacher with a knife. This, after she saw him take down her entire security force.

I’ll let you guess whether Child’s franchise ends with this book. It does for me.