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Massive extraction of groundwater can resolve a puzzle over a rise in sea levels in past decades, scientists in Japan said on Sunday.

Facebook resumes trading on Wall Street on Monday with shares being closely watched to see how well they stand on their own after stumbling out of the gate in a historic but lackluster debut.

(AP) -- Pakistan blocked the social networking website Twitter for much of Sunday because it refused to remove tweets considered offensive to Islam, said one of the country's top telecommunications officials.

(AP) -- Yahoo Inc. may finally be nearing a deal to sell a part of its prized stake in the major Chinese e-commerce provider Alibaba.

In the world of electronics we have impedance; the combination of all forces which oppose the flow of electric current. Often times we have circuits with different impedances, 50 ohms for RF, or 75 for cable TV. It’s pretty important to use the right coax in these circuits, else you’ll be wondering why your RG-58 antenna feed line doesn’t give you anything good to watch.

It’s pretty important to match impedances when connecting different circuits. Apart from the obvious flaws such as a 50 ohm load blowing up a 300 ohm amplifier, there are subtler things such as signal reflection and destructive interference which might just be enough to break whatever it is your playing with. RF mosfets are not cheap! But how could we match impedances? Well we could always use a transformer, but those are rather expensive and bulky. What if we only have a box of resistors to play with? Well, we could build an attenuator! Most of you probably know what an attenuator is; if not, it’s a de-amplifier. Simply put, it’s a circuit which reduces the strength of a signal. Often these are called ‘pads’ in the RF world, and the pad most often used is the pi pad. By looking at the network’s schematic it becomes rather obvious *why* we call it that.

It looks like a π.

Now our guests want a 50 ohm signal attenuation of 3dBm, or 50%. Let’s pick some toppings for our pi then, shall we?

When Z=50, R1 and R3 equal…

[292.4 ohms].

Now R2 equals…

[17.61 ohms]

Well that was a pain. Luckily, there’s a cheat sheet for this.

So now we have our values, and assuming a 50 ohm load everything should work just fine. But wait! Somebody F*cked up and put a 300 ohm feed line on the end of the pad! Crap. Let’s look at the resistance values of the network now, from A to ground. I’m assuming you should know how to calculate resistances…

…105.7 ohms. That’s near double the 50 ohm input impedance and is going to wreak all hell upon the other circuitry. Sure, it does its job of reducing the signal 3dBm but still.

Now here’s the neat thing. Let’s pick some new resistor values so that we attenuate by 10dBm, or about 90%. According to our cheat sheet we’d need 71.75 ohms of attenuating resistance and 96.25 ohms to ground on either end. What’s the impedance mismatch now?

57.78 ohms, or 7.78 away from 50. That’s a lot better than before, and should actually be usable as an impedance matching network. Sure, you lose 10dBm or about 90% of your signal strength, but that’s nothing that can’t be compensated for by putting a Class-C amplifier in series with the attenuator. Even with an active component it’s still cheaper and smaller than a transformer. What I’m trying to prove here is that pi pads can be used as the poor man’s impedance matcher; as attenuation goes up the impedance mismatch goes down.

What’s nice about resistive pi pads is that they are ultra-wideband; since there are no reactive components this network will always attenuate by 10dBm and always match the impedance by 7.2 ohms. An inductive network such as a transformer might not work at both 200kHz and 200MHz. Actually, it certainly won’t work! Capacitive networks would have the same limitations.

</ LESSON>

Filed under: Ask Hackaday

There’s no question that Apple has their industrial design down pat; comparing a cell phone charger made by Blackberry or Motorola to the tiny 1-inch-cube Apple charger just underscores this fact. [Ken Shirriff] posted a great teardown of the Apple iPhone charger that goes through the hardware that makes this charger so impressive.

Like most cell phone chargers and power supplies these days, Apple’s charger is a switching power supply giving it a much better efficiency than a simple ‘transformer, rectifier, regulator’ linear power supply. Inside the charger, mains power is converted to DC, chopped up by a control IC, fed into a flyback transformer and converted into AC, and finally changed back into DC, and finally filtered and sent out through a USB port.

The quality of the charger is apparent; there’s really no way this small 1-inch cube could be made any smaller. In fact, if it weren’t for the microscopic 0402 SMD components, it’s doubtful this charger could be made at all.

Comparing the $30 iPhone charger of a cheap (and fake) iPhone charger, the budget charger still uses a flyback transformer but there are serious compromises of the safety and quality. The fake charger doesn’t use a power supply controller IC and replaces the four bridge diodes for a single diode to rectify the AC; a very efficient cost-cutting measure, but it does lead to a noisier power supply.

There’s also the issue of safety; on the Apple charger, there is a (relatively) huge physical separation of  ~340 VDC and your phone. With the off-brand charger, these circuits are separated by less than a millimeter – not very safe, and certainly wouldn’t be UL approved.

It’s worth pointing out that [Ken] compares a similar $7 Samsung charger favorably to the $30 Apple charger. Both are functionally identical, but Apple also has their  marketing down pat, to say the least.

Tip ‘o the hat to [George] for sending this in.

EDIT: In case a 1-inch cube wasn’t impressive enough, check out the euro version of the iPhone/iPad charger. It supplies 1A @ 5V, and isn’t much thicker than the USB port itself. Thanks [Andreas] for bringing this to our attention. If anyone wants to do a teardown of the euro version, send it in on the tip line.

Filed under: hardware, teardown

A pioneering study to gauge the toxicity of quantum dots in primates has found the tiny crystals to be safe over a one-year period, a hopeful outcome for doctors and scientists seeking new ways to battle diseases like cancer through nanomedicine.

We’ll admit that we haven’t been following Minecraft like we used to; its been a while since we’ve seen something amazing in Minecraft, but [eloraam]‘s 6502 emulator (part of her RedPower Minecraft mod) takes the cake.

The RedPower mod adds a lot of industrial technology to Minecraft. Pumps, solar panels, and pneumatic tubes to move blocks around are the staple of this mod, but with the addition of a fully emulated 6502 computer, Minecraft moves from an anachronistic medieval-themed steampunk aesthetic to a full-on machine age, mainframes everywhere style.

The heart of the 6502 portion of the RedPower mod are three craftable blocks; a CPU, a monitor, and a disk drive. All these blocks are connected together with ribbon cables and can interact with other blocks in the Minecraft universe. The CPU is an emulated 6502, with a few instructions borrowed from the 65816 and the addition of MUL and DIV. It’s possible to program this computer in assembly, but [eloraam] a Forth interpreter with the OS to make programming a little easier.

It’s been almost two years since we first saw the beginnings of a CPU made in Minecraft, but this mod takes everything to the next level. In actuality, this isn’t very different from the game [notch] is currently working on; both feature an emulated 80′s era computer that can do all your in-game bidding. We can’t imagine anything better to get us hooked on Minecraft again, and we’ve got to commend [eloraam] for some seriously awesome work.

After the break is a 23-minute tutorial on the functions of the RedPower CPU, as demonstrated by Minecraft aficionado [direwolf20].

Filed under: classic hacks, toy hacks

In a decision we completely agree with, these industrious young women decided that playing in the rain would only be more fun if it included an interactive light show. They wanted the rain itself to cause LEDs in their umbrella to light up. To achieve this, they put piezo sensors on each of the 8 panels of the umbrella. When that panel gets hit, its LEDs light up. You can see in the video after the break that it was quite effective.

Their next step should be to somehow increase the resolution to be similar to this one, while maintaining interactivity with the rain. How would you sense rain drops with more definition though?

[via Adafruit]

Filed under: led hacks

[Matthew Riese] got frustrated waiting for the future to arrive so he could have his flying car. He decided to take things into his own hands and construct the closest thing he could. This turned out to be a hovercraft. Not only that, but he thought that the most fitting shape for this thing would be a DeLorean.  We can’t say that we disagree with him. Unfortunately, there isn’t a whole lot of information on his build. There is this cool video on his kickstarter page (don’t worry, he got funded back in 2010). To make up for the fact that the build information is sparse, we’ve found you some plans to make your own hovercraft. Just add whatever shape body you want, though we have some suggestions.

[via Makezine]

Filed under: transportation hacks

The recent excesses of Wall Street may be big news but behind the headlines there's another story: When it comes to men and women stockbrokers, someone is taking home a bigger paycheck.

(Phys.org) -- An underwater turbine being used for harnessing tidal power to generate electricity for homes and businesses has successfully completed its testing period in the island of Eday, one of Orkney’s northern isles. The machine marks the first to be used in Scotland’s ambitious tidal power project, with more turbines at more sites planned. Scottish Power Renewables (SPR) says that the completion of the test period is an encouraging step up in Scotland’s tidal power initiative. The turbine was lowered into position during winter storms as a test device to prove that the technology can operate efficiently in Scotland’s fast-flowing tides.

Australian authorities were racing to secure a cargo ship drifting off the Great Barrier Reef, with one expert saying it was "sheer luck" it had not hit a reef near the World Heritage-listed site.

(AP) -- For Facebook founder and CEO Mark Zuckerberg, it was quite a week - from birthday, to IPO, to I DO.

(Phys.org) -- Google's September 2011 patent that was filed for a wearable display device was granted this week, which suggests that its envisioned heads-up display device can be controlled by infrared markers in the form of devices worn on the hands, such as fake fingernails or rings. The patent says, “A wearable marker may take the form of a ring, a bracelet, an artificial fingernail configured to be affixed to a fingernail, a decal configured to be affixed to a fingernail, or a glove, among other possible wearable items."

A Malaysian researcher known for finding new amphibian species said Friday his team had discovered at least one new species of frog in studies he said highlight Borneo's rich biodiversity.

A broken-down cargo ship was drifting towards the fringes of Australia's Great Barrier Reef Saturday, with fears of major damage if it were to run aground at the World Heritage-listed site.

(AP) -- The metaphor is an easy one, overused and perhaps even a bit overwrought. We are forging forward into a digital frontier, leaving convention behind, traveling without guides into an uncharted virtual land where progress and profits are forever around the next bend.

(AP) -- A watchful eye has arrived on San Francisco's bar scene, but not to keep you in check. It just wants to check you out.

(AP) -- Authorities in China have approved Google Inc.'s bid to buy phone maker Motorola Mobility, clearing the way for the $12.5 billion deal to close early next week.