Sparkfun Free Day Over

SparkFun.comFree Day is over at SparkFun.com. Over $100k was given away in just under 1 hour and 45 minutes. According to their site they had over 1,000 orders and nearly 70,000 unique visitors.

USB 3.0 Released

USB 3.0 Cable
USB 3.0 Cable

USB 3.0 spec has been released! Varying reports, but it looks like USB 3.0 will have 10x higher data rates (4.8Gb/s vs 480Mb/s), higher current (900mA vs 500mA), and a new interrupt driven protocol. You may notice that they have changed the female plug which means I wouldn’t hold my breath when it comes to backwards compatibility. Luckily, we’ve got until 2010.

Lethal Electricity Explained

While searching for information on the lethal potential of electrical shock I came across an article by Zach Eveland that provides a clear and simple explanation.

Play safe kiddies.

“…it’s the current that kills, in most cases by interfering with the normal operation of the heart. Be careful though – with the right conditions, shocks way below 1 Amp can be lethal. In designs where you are trying to prevent electrocution, 5 milliamps is considered the upper limit of safe operation. Notice that that’s 5 MILLIamps – barely enough to light an LED.

“The thing to measure is how much current is flowing through the heart and you have to assume the worst case; that someone is holding positive with one hand and negative with the other, letting the electricity go right through their chest and heart. Body and skin resistance, hand-to-hand, varies but 10 kohm is a safe figure to work with (though it can be even less with wet hands and can go much higher, up to hundreds of kohms).

“Here’s an example for figuring current: with a 9V battery and 10 kohm of body resistance, if I hold positive with one hand and negative with the other, the current through my heart is equal to 9V divided by 10 kohm or 0.9 mA – in the safe range.

“One more warning; be careful with this – keep your hands dry, don’t stand in water, have somebody around when you’re testing, don’t shock people with weak hearts, etc.

“In general, [to produce a safe shock, something I don’t recommend – tigoe] you want a high-voltage, very low-current source of electricity, ideally DC since AC voltages are more likely to interfere with heart rhythm. A good value would be several hundred volts at way less than 5 mA. The best design would limit the amount of current to a safe level. Luckily, there are pre-built devices that do this (though I sure as hell won’t vouch for any of them): search eBay for “nerve stimulator” or “TENS”. Other options would be the peizo igniter from a cigarette or BBQ lighter or the flash unit from a disposable camera.

“Again, be safe and smart, and good luck.”
-Zach E