Amateur Logic has been podcasting interesting projects including the active cantenna in episode 3. Their latest episode is straight from the Capital City Hamfest. There is an ARRL review of the amateur radio effort during Katrina, a presentation about Skywarn, and an inspiring amateur satellite radio demonstration. There is not much technical information, but it is a great introduction to what being a ham is about.
To learn more about amateur radio visit arrl.org or amsat.org.
Theodore Gray, co-founder of Wolfram Research, Inc makers of Mathematica, wrote up an amazing article on making your own light bulb. The project is quick and simple, but a little pricey:
- Element: Tungsten
- Time: 30 minutes
- Cost: Roughly $50
Edison’s first mistake was living before tungsten wire was available. Tungsten is way better than carbon as a filament material, and now you can find it in any metal-supply shop… His second mistake, repeated in classroom physics demonstrations to this day, was using a vacuum to get the air out of the bulb…
The site is now running on a brand new layout! The colors are definately an improvement. There is only one problem in Internet Explorer (of course). The shadow at the top of the content seems to get placed in all the comment nipples. Quite the bug, reseting #main2 every .comment-nipple. If I place padding at the top of #main2, it even copies that! This problem is driving me nuts!!
Feel free to comment. Especially on how horrible Internet Explorer is…
If you have ever wanted to play pong on a three dimensional display, then this one is for you. There are 1,000 white LEDs in the matrix that can refresh at a rate of 60 fps.
There are videos included, and they also dance to music. I don’t imagine the videos do the display any justice, though.
LED lighting is becoming increasingly popular in fish tanks, case mods, and even household lighting
. This article intends to be a comprehensive guide to their advantages, powering them, and creating dimming solutions.
Why use LED lighting?
LED lights are extremely efficient compared to standard incandescent lighting. No other lighting source outputs as many lumens per watt. They are particularly efficient at producing a single color of light. Other light sources have to produce the entire spectrum and optically filter out unwanted colors. However, LEDs can be manufactured to produce only one wavelength of light. This makes them particularly useful in stop lights.
Another advantage to LEDs is their operating temperature. Most available today can be function for hours and remain cool to the touch. Directionality is another key property. They only emit light over a relatively small angle. This can be advantageous for reading lights, but hinders performance when attempting to light an entire room.
If the advantages of LED lighting interest you, Myths Busted, LED Lighting is an excellent article by a researcher in outdoor lighting solutions. (And the source of most my information.)
Powering your LEDs with a DC source
Warning: Driving your LEDs with too much current will permanently disable them.
If you attach LEDs directly to an unlimited power source, they naturally draw enough current to blow themselves out. Therefore, the driving current must be limited with a resistor. The relationship as described by Ohm’s Law, is V = I*R where V is the voltage over the resistor, I is the driving current, and R is the limiting resistor. Two example circuits are shown below. These particular LEDs are rated at 25mA and are powered by a 12 volt regulated supply.
Each white LED gives a voltage drop of 3.6 volts. As an example for a 12 volt light, you can run a maximum of 3 white LEDs in series at full power (3.6 x 3 = 10.8 volts drop). Subtract this from your supply voltage of 12 volts to get the additional voltage that must be dropped (in this case, 12 – 10.8 = 1.2 volts of additional drop needed). In this case, 1.2 volts of additional drop / .025 amps (25 ma) = 48 ohms… resistors are rated in watts. So in this case, 1.2 volts x .025 amps = 0.03 watts. A 1/4 watt resistor would work fine.
The tutorial above also explains how to construct a 12 volt voltage regulator from any 12+ volt DC source. Voltage regulation is highly recommended because large shifts in your driving voltage can cause the driving current to increase and burn out your LEDs!
If you are in doubt of your calculations, use one of the many LED resistor calculators.
Using an AC source to drive LEDs
It is also possible to convert an AC source to DC. My favorite way to accomplish this is with a bridge rectifier as shown below. As an added bonus, R is easily calculated using the method above.
In operation, a DC voltage of around 170 is produced from the bridge rectifier and 50uF capacitor. The capacitor value is not critical and can be anything from 20uF or more… To find the resistor value and wattage, multiply the number of LEDs by the individual LED voltage. Then subtract this number from 170 and divide the result by the desired current (usually 20 milliamps).
Dimming your LEDs (with PWM)
Using pulse width modulation (PWM) to dim your LEDs is extremely important! Simply decreasing the input voltage yields unreliable results and potentially reduces their life-span. Pulse width modulation basically pulses the source voltage on and off so quickly that your eye is unable to distinguish the difference.
PWM can be implemented using a variety of methods. The simplest is switching on/off the output of a microcontroller. There are also several circuits that implement PWM. My favorite method uses two comparators. The details are excruciatingly painful and may deserve their own article someday.
The first example uses the standard op-amp oscillator circuit to generate a triangular waveform which is level-shifted and fed to a comparator (e.g. LM339) to give the PWM waveform.
Purchasing LEDs
LEDs are available all over the Internet. Recommending a single source or particular LEDs is hard as prices, projects, and the LEDs themselves may vary. If you are planning on starting an LED lighting project, it is best to do some research. For smaller applications, like a reading light, it may be more cost-effective to skip out on the top-of-the-line and buy a few more (relatively) cheaper LEDs. If you want to build a moonlight for your fish-tank, then you don’t need all those lumens blinding your fish!
Digg! this article…
Afraid the government is trying to track you? Want to disable your old credit cards wireless signal? Need to get that new backpack out of Macy’s without getting caught? You need to disable those RFID tags.
There are several ways to deactivate RFID-Tags. One that might be offered by the industries are RFID-deactivators, which will send the RFID-Tag to sleep. A problem with this method is, that it is not permanent… The RFID-Zapper solves this dilemma… It generates a strong electromagnetic field with a coil, which should be placed as near to the target RFID-Tag as possible. The RFID-Tag then will receive a strong shock of energy comparable with an EMP and some part of it will blow, thus deactivating the chip forever.
If this zapper was bigger, then I could mess up Wal*mart’s inventory for months.
Recently, RFID was in the headlines for being crackable by cellphone. At first glance, this article does not seem very extrodinary. SHA-1 encryption is weak and any engineer knows a cellphone is just a tiny computer with an antennae. However, the headlines fail to tell the entire story.
If you didn’t know, RFID tags do not contain batteries. Instead, they draw power electromagnetically from the reader. Shamir uses a directional antennae to monitor the power consumed by the RFID tag.
“The reflected signals contain a lot of information,” Shamir said. “We can see the point where the chip is unhappy if a wrong bit is sent and consumes more power from the environment…to write a note to RAM that it has received a bad bit and to ignore the rest of the string,” he added.
By monitoring power consumption, they are able to tell exactly which bit in the pass-phrase incorrect. Considering that half the bits could be guessed correctly as zero or one, it would only take 128 tries to crack a 256 bit pass-phrase. On the bright side, it ignores the proceeding bits instead of giving them away as well.
If you were wondering, a cell phone has all the hardware necessary to replicate this attack. Hopefully, 3rd party software is restricted from processing incoming RF signals directly.
