Overview
The number of victims are increasing every year, and so are the costs.
Here are a couple of examples:
Last June, park rangers spent four days trying to rescue six members of a British climbing team. They spent four days stranded on a steep slab of ice near McKinley's summit, suffering many injuries. The story was front-page news locally for four straight days before making national news. The cost to the military and Park Service totaled $221,818.
A more common story: A climber collapses on Mount McKinley with altitude sickness. Rescuers in a special high-altitude helicopter are called to pluck him off the mountain. The cost: $1,892
Who pays all these fees? As NBC's Tom Brokaw reported during a June broadcast of the evening news after one particularly harrowing rescue on Mount McKinley: "And you, the taxpayer, are paying for it." This is true. How can we decrease such a waste of taxpayer's money? Simple, find a way to locate these careless thrill seekers so they can easily be rescued.
This is a major problem for search and rescue groups. Instead of using money to replace old and obsolete equipment, it is spent on man-hours searching for victims.
Threshold Postulate
Any certified helmets should be able to absorb a certain amount of impact forces. For Snell B-95 standards, a five-kilogram instrumented headform is placed in the helmet and dropped upside down onto an anvil 2.5 meters below. In order for the helmet to pass, the instruments inside the headform must register less than 300 g's during the impact, or in some cases less than 250 or even 200 g's. With the weight of the headform, this equals to roughly 11 000 Newtons. We have assumed that any forces above this certain threshold will cause severe harm to the user and therefore will be in the need of assistance. The force sensors and voltage comparator will then be calibrated to this threshold. Note that, the 11 000 N threshold is only a postulate. With time, statistics can be found concerning this matter and a better postulate can be formed. Tests can also be done concerning brain waves of the unconscious versus the conscious to allow the use of brain-wave sensors instead of force sensors.
A) Since the maximum required voltage for the force sensors is around 5.5V and the maximum voltage for the GPS circuitry is 6.0V, 4-AAA batteries will be connected in series, providing enough power for all the circuitry.
B) The LMV7255 voltage comparator (http://www.national.com/ds/LM/LMV7251.pdf) is a low voltage comparator, which can operate at supply voltage range of 1.8V to 6.0V. It features an open drain output. This allows the connection of an external resistor at the output for varying threshold voltage requirements.
C) The Global Positioning System (GPS) circuitry used for the helmet will be based on the Magellan 310 GPS receiver http://www.magellangps.com/ Global Positioning It can navigate over 15,000 worldwide cities using its 12 parallel-channel receiver, which provides superior tracking performance under the toughest conditions. It also has an integrated 10-year lithium battery backup.
D) A constant voltage is sent to the force sensors, if the wire connecting the helmet to the control unit is broken or disconnected, the current stops flowing and overrides the voltage comparator, this will signal the GPS device. The other condition for the GPS signal to be activated is if the force sensors feel an impact above 250g.