WIFI Theremin

Midnight Research Labs describes a nifty theremin hack implemented by detecting signal strength of a WIFI signal. Python source is available to examine.

link [kudos HackADay]

Bonus Hack: Zevv implements an ultrasonic theremin, emitting ultrasonic chirps from laptop speakers,  detecting reflection to the microphone, and driving a tone generator.

Random Friday: What We Hike 3

Pix from neighborhood of Dog Canyon in southern New Mexico, 2008.

Related Posts: What We Hike 2, What We Hike

More Bacon

Check out our new blog theme: now with more bacon.

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Related Post: Countdown

Betamax Decision

25 years ago today, Sony Corporation of America v Universal City Studios, Inc was decided by the Supreme Court of the United States, affirming that time-shifting is fair use and does not infringe on copyright.

[flash] [video link]

Random Friday: What We Tour 2

We had the opportunity to explore Las Vegas, New Mexico (not the other one).

Old western towns along the rail line tended to have one fancy hotel to make a good impression on visitors, and the Plaza Hotel on the square of Las Vegas has been restored. We took a room, and can recommend a stay for history fans.

Las Vegas has over 900 buildings listed on the National Register of Historic Places. Take a random walk and absorb the architecture.

Carnegie Library, 1903, only surviving Carnegie Library in New Mexico, with a nod to Monticello

Related Posts: What We Tour

Voyager 510 Headset USB Charger

We often use a Plantronics Voyager 510 Bluetooth headset with our computer, so we can a) listen to streaming video/audio without inflicting our choices nearby innocents,  and b) remain untied by a corded headset when we jump up with sudden inspiration.

A previous post explored building a USB charger for our cell phone, and we decided to try the same thing to charge our headset. Over time, we are trying to reduce the number of wall-wart chargers used with our laptop, so we don’t have to carry chargers on business trips and to eliminate wasted electricity when the charger is plugged into a wall socket and not charging a gadget. The USB charger for our cell phone used zero standby current, and we hoped to do the same for the headset charger.

USB Standards

A USB port can supply 100mA at 4.75 to 5.25volts. A higher current, to a maximum of 500mA, can be drawn if the port follows a particular handshaking protocol.

USB Pin-Out
















Voyager 510 Charging Requirements

The headset charger has a barrel type plug with diameter 3.0mm and only 3.5mm in length. Notice that the barrel has a reduced diameter region near the end to help the headset “grip” the plug.

The open-circuit voltage measures 5.5V, and the charging current was 63.8mA. This is within the 100mA current limit of USB, and the voltage is close enough to the USB supply voltage that we suspect a direct connection to the VBus and Gnd conductors of a USB cable will successfully keep the headset charged. See the “Design and Experiment” section of a previous article for more in-depth hand-waving.


Usual Disclaimer: Use this information at your own risk. We are not responsible for damage to your headset or computer.

We couldn’t find a similar connector anywhere on Digikey or other electronics parts vendors we searched. (If anyone has found a source, let us know.) Reluctantly we purchased a spare charger on Ebay for less than $5, just to salvage the connector.

Take a spare USB cord and cut off the series “A” type plug, leaving a few centimeters of cable. Remove a centimeter of outer insulation and shield, exposing four wires. You can cut off the green (D+) and white (D-) wires– they are not needed here.

Cut the spare charger cable 10cm from the connector end, and remove one cm of outer insulation, exposing a red and yellow wire. The red connects to the inner conductor of the plug, 5V, and the yellow connects to outer GND.

Strip insulation 0.5cm from the wires. Thread a length of shrink-wrap tubing on the cable, and twist the red wires together and solder. Twist the yellow wire from the charger plug to the black wire from the USB plug, and solder.

Use a bit of electrician tape to insulate the conductors, and wrap more around both wires for strain relief.

Check continuity with a meter. Slip the shrink wrap tubing over the solder joints and apply gentle heat until snug.


It works!

Related Posts: V176 Cell Phone USB Charger, Power to the Programmers

OS Wars Film Festival

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Related Posts: Tech Support Film Festival, Theremoid FilmFest, Theremin Video Film Festival

Lurching Toward Digital

The USA DTV coupon program is out of money. The vouchers are intended to help purchase digital converter boxes for consumers with older televisions (and analog TV tuner cards) needed to convert digital broadcasts to the legacy format after the February 17, 2009 deadline for stopping analog broadcast TV. $1.34 billion was reserved for the program.

Now the advocacy group Consumers Union is urging a delay in the transition date.

[kudos Gizmodo, Washington Post]

Related post: Switching to Digital TV

Solar 2: Mounting the Panel

  • December 31, 2008
  • General

[This is the second in a series of articles describing installation of a solar hot water system.]

The solar panel was not in stock at AAASolar, so we had to wait a couple of weeks for it to be freighted to the shop. We have access to a truck, so we could pick up the goodies at the shop and not have it delivered.

We could have transported the solar panel and storage tank in one trip, but decided to truck them separately to avoid any possibility of damaging the panel. Cracked glazing would have made me very sad.

Here is the storage tank protected for the trip:

The solar panel is solid and heavy, approximately 150lbs, too massive for one or two people to carry up a ladder. In retrospect, the easiest way to get this panel onto a flat roof is crowd-sourcing: get six good friends or family members with ropes pulling and pushing the panel together. Sadly this particular day I was (almost) friendless, so cleverness was in order. Phil and I fastened a 4×4 crossbar between two ladders, affixed a pulley in the middle, and tied a rope harness around the panel. We parked Phil’s jeep with electric winch in the garage underneath the ladders (barely seen in this photo because the dark-colored vehicle is in shadow).

The winch and pulley pulled the panel up to the roof, while one person on the roof steadied the panel using ropes. Again, this technique worked but is overly complex– use crowd-sourcing instead.

I could not work out how the mounting hardware fastened to the panel, and no documentation was included. AAASolar had no instructions for this particular model, and recommended we contact the panel manufacturer SunEarth. No instructions were found on the web site– a helpful person on the phone faxed us the drawings we needed.

One thing apparent from the drawings is that the panel is mounted  with the shorter side along the roof, unlike most panels we see installed in this part of the country: Good to know!

We needed to bolt the panel mounting hardware to the roof with long lag bolts sunk into roof joists. The problem was finding the roof joists! Two different stud finders gave no consistent readings on the roof (and yes, we did try the trick of using cardboard over this rough surface), and we drilled two or three holes that totally missed a joist. It’s bad enough to be drilling into a perfectly nice roof, but to miss the timber beneath and have to patch the hole is most embarrassing.

Finally, we hit upon the trick of drilling a test hole at a shallow angle, and then using a coat hanger wire as a probe to test for where the joist is located.

Once we know where one joist is, we should be able to find the next one, assuming the joist spacing is the same as over the garage, where joists are visible. One final indignity: the joist spacing was different on this section of the roof, so we had to drill another shallow angle test hole as before and patch it afterward. We used 2×4 boards as footers to help spread the weight on the roof surface, and screwed long lag bolts through the metal mounting block, the wood footer, and into the roof joist.

Albuquerque has a 35 degree latitude. We elevated the panel to 55 degrees, to give more sun in the winter when the panel needs it most.

Related Posts: Solar 1, Power to the Programmers