Testing Glycerin as a bubble medium

Posted on June 16, 2012 by Jay

The tube on the left is filled with Glycerin. I like how the bubbles float up much slower and are more defined. Also, because the Glycerin has a lot of “micro-bubbles” in it, the light from the RGB LED’s in the bottom of the tube diffuses out of the mixture much more, and gives the whole tube a colored glow effect.

One problem is that if I want to make larger bubbles (than in the video above) I need to increase the size of my nozzle. The current small nozzles will make “separated” bubbles if I run air through them for too long, demonstrated below in this video:

Of course, I had to try making bubbles really fast! (The upper limit in Glycerin is slower than in water…)

Glycerin is relatively safe (msds) as long as you don’t eat it, although it can cause skin and eye irritation if you don’t wash it off. Clean up is easy, as it dissolves in water, but it’s more messy than just plain water, and costs a lot more! Even buying in bulk, it takes $8 worth of Glycerin to fill a 6′ long 1″ square tube!

Bubble Display Videos

Posted on June 13, 2012 by Jay

I have been playing around with the timing for how long to turn on the air pumps (as well as the delay time between bubbles). This video is my “favorite” so far for the solid bubbles (on the left) 30ms on-time, and 300ms delay. Obviously, the aquarium air stone tube (right side) needs a longer delay to separate the air pulses.

Of course, I also tried playing around with super fast bubbles!

And with the smallest bubbles I could make (the electronics can give a 1ms pulse, but the motor/air-pump needs at least 8ms of power to eject a bubble…)

Bubble Display Prototype 1

Posted on June 13, 2012 by Jay

I have the physical structure, electronics, and pneumatic systems all integrated (for 2 of 6 channels) on my first prototype for the Bubble Display. The electronics are mounted on one side of the upright board, while the air pumps, check valves, LED lights and acrylic tubes are mounted on the other. (Click photos for larger versions)

And here is a video of the system driving two channels (tubes of water). This is a 10ms bubble size, which is quite small. I will be experimenting with various lengths of time to drive the air pumps to make bubbles of different sizes, as well as experimenting to find out how small of a delay I can use without having the bubbles run into each other as they rise. (The length of the tube will affect that as well, so it’s just about time to make some six foot tubes!)

Acrylic Column #1 (Bubble Display testing)

Posted on May 22, 2012 by Jay

I finished test column #1 today. I was able to cut the extruded acrylic tube using a miter saw with no major difficulties, and pulled it across a piece of sandpaper on a glass backing to try to ensure that the end was perfectly flat. I had to use a good amount of solvent to weld the 1″ square bottom plate to the bottom of the square extruded acrylic tube. Even after my initial weld, it had some pinhole leaks that would “weep” water. I fixed them by turning the tube sideways and wiping a liberal amount of solvent along each of the four seams, allowing it to seep into the gaps (and/or melt acrylic into the gaps.)

As far as I can tell Continue reading →

Missed Schedule for wordpress posts due to .htaccess password protection blocking wp-cron.php

Posted on April 26, 2012 by Jay

I recently set up a private blog that is fully password protected using an .htaccess file. (Users have to enter a username and password to view anything on the blog.) Everything was working well until we tried to set up posts scheduled to publish in the future. They would not post. The dashboard would show “Missed Schedule” and we would have to publish them manually.

After lots of head scratching, I finally figured out what was causing this. Apparently wordpress will call the wp-cron.php file every time a user views a page. HOWEVER, because the web server is doing this, and not the user’s browser, if the wp-cron.php file is protected by a .htaccess user authentication system it will not load (because wordpress doesn’t have the correct username/password!). So none of your scheduled actions will take place.

The solution is to allow (only) that file to be loaded without the normal username/password check in your .htaccess file like this:
#Require username and password for all files! AuthName "Enter your username and password:" AuthType Basic AuthUserFile /home/yourdirectory/.htpasswd Require valid-user

#Exclude the wp-cron.php file! <files wp-cron.php> Order Allow,Deny Allow from all Satisfy any </files>

Of course, if your blog is password protected, the wp-cron.php file won’t get hit until somebody logs in to view the blog…but at that point any tasks that are pending will activate.

Spare One Phone – Dead on Arrival – Two Red LEDs

Posted on March 25, 2012 by Jay

UPDATE: I called the company twice (once on Monday and again on Tuesday) and on Tuesday after asking a few questions they shipped me a new phone (arrived on Saturday and worked correctly!) and a label to ship back the defective unit. (I also emailed them on Sunday, and received an email reply 8 days later, after already receiving the replacement phone…so I would recommend persistent phone calls (it took a few tries to get to a human instead of voice-mail) over email.

Original post:
I purchased a SpareOne phone, which is a very simple GSM handset that is powered by a single AA battery. It has even less functionality than the Motorola MotoFone F3, as it has no display other than two indicator LEDs, so you can’t send or receive SMS messages. It comes with an Energizer Ultimate Lithium battery which has a 15 year shelf life (if you keep the battery disconnected from the phone with the provided plastic pull strip) and offers “up to” 10 hours of talk time on a single battery. My invoice number was 393, so it looks like I was within the first few hundred orders.

Unfortunately, when I received the phone and pulled the battery guard out, instead of turning on it just lit up both LED’s solid red (which I assume is some type of error code, although it is not mentioned in the small instruction sheet that came with the phone. I have tried a new battery, veracious press combinations of the ON button, and the keylock button, etc, but have gotten none of the feedback beeps demonstrated in the “how to” videos.

I will be calling their support line on Monday to see if they have any advice for how to re-set it, or return it for a replacement.

Boost Converter Schematic

Posted on January 22, 2012 by Jay

I have drawn up a schematic (click to enlarge) of the high current and sensing portions of my maximum power point tracking (MPPT) 2-phase boost converter battery charger circuit. The schematic does not include the micro-controller, MOSFET gate driver IC, and associated power supplies, as those items are on the (relatively) low-power side of things.

What do all of these things do?

L1, Q1, and D1 – These three components make up the heart of the boost converter. When Q1 turns on, power builds up in L1 as the current rises. When Q1 turns off, all of that power exits via the only available route (out past D1) and the voltage is boosted as the inductor (L1) resists the current change. If you turn Q1 on and off very quickly (under control of the micro-controllers’ PWM output via a MOSFET gate driver) it raises the output voltage higher than the input voltage.

Continue reading →

Using the Microchip PIC Kit 1 with Linux

Posted on January 1, 2012 by Jay

The PICKit 1 is a combination programmer and development board for midrange PIC micro-controllers. In addition to being able to program FLASH pic devices, it also allows them to run and access 8 (charlieplexed) LED’s, a pushbutton switch, and a potentiometer. It’s a great little board for learning the basic of micrcontroller programing, but unfortunately it is not supported by Microchip’s new MPLAB X software (that is written in Java, and supports Linux/Mac in addition to Windows).

You CAN however use the PICKit 1 under linux. The piclab software is supposed to support it (I have not tested this). I use version 1.6 of the PicKit1 flash usb programmer for unix. Even the newest 1.6 version reports checksum errors after writing the hex file, but it does work correctly.

To make it work as an external program in MPLABX I had to select the “format HEX file for download” option under the Linker so that it would not fill all 2048 flash bytes when the program was smaller than that. I am able to manually run the usb_pickit command after building to flash the code, but it’s kind of annoying, as that program has a problem verifying the checksum and reports an error every time (which is interpreted as a build failure) plus, I have to run mplab X with root permissions to be able to access my USB port.

Solar Panels on the Electric Truck

Posted on November 16, 2011 by Jay

I purchased two used GE Energy GEPVc-175 watt solar panels and mounted them to the bedcover of my truck using 10-24 machine screws and T cone washers as rubber vibration dampers. Each panel weighs 31 pounds, and is rated to deliver up to 175 watts of power in full sun (at around 36 volts each, or 73.4 volts at 4.7 Amps in series). I am still waiting on a group of Georgia Tech ECE students for the magic box that does maximum power point tracking (MPPT) and voltage boosting to charge my 120 volt battery pack, but I hope to be generating 1-3 miles of my daily commute from the sun soon. As my daily commute is 4 miles, this can be a significant percentage of my total energy usage.

I have calculated that in the summer the panels are far enough behind the cab that they will not be shadowed by it, even if I have to park facing south. In the winter and early spring / late autumn I need to park facing north to avoid shading a strip of the solar panels.
I still need to figure out a way to tilt the panels towards the sun to collect as much energy as possible. This is especially critical during winter, when the solar angle is way off of vertical. As the bed cover tilts, AND the bed of the truck can tilt (the other way) I figure I can work something out (with a few pieces of wood cut to the correct height, or linear actuators if I want to get fancy.

Ferrofluid Sculpture test 2

Posted on November 6, 2011 by Jay

After buying some strong rare earth magnets I re-tried my ferrofluid levitating sculpture. The main problem is that the ferro-fluid moves to the poles of the magnets (top and bottom, with gravity favoring the bottom) and does not surround the sides of the magnets. It was also hard to get enough small magnets to fit under the main magnet (as they repel each other), so I had to include a screw in the middle to get the weight correct.

Note: Working with Ferro-fluid is dirty and messy. If magnets snap together they can throw dark oily fluid which stains just about anything. Be sure to have lots of paper towels on hand, jars/shields under/around everything, and don’t work in a nice room. Dish detergent and abrasive scrubbing will eventually get it off of most surfaces that are not porous. Wear disposable rubber gloves and use disposable pipettes. Wear disposable clothes. Don’t use any of your wife’s kitchen appliances or instruments that you can’t afford to replace.

Update: After floating under the magnetic levitation for 24 hours, the ferro-fluid became much less “spiky” and eventually the drops at the end of the magnets became spherical.

Also, cleaning ferrofluid from a magnet is almost impossible.

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