Light - Photoresistor
Photoresistors are light-dependent resistor (LDR), also referred to as a “photocell”. Resistance across them decreases with exposure to light. Wired from an analog read pin to ground.Read from an analog read pin.
Pros
+ Easy to detect - The kind of light detected is the same wavelength we perceive naturally. Being able to easily see the input signal makes debugging significantly easier.
+ No additional hardware - In most demonstration conditions, light - in the form of daylight, synthetic fluorescents, LED, and halogens - is present
Cons
+ Inconsistent - Visible light levels vary A LOT between spaces. This makes for a bad output for a linear actuator.
+ Reacts to ambient light - In the context of a full-scale implementation, a photocell input would result in the bridge delaying for clouds, or any other opaque object that could move over the bridge path.
+ Reaction not limited to the car - Part of the appeal of a bridge that materializes out of nowhere is the fact that it only works under certain conditions, or for certain people.
Magnetic Field - Hall Effect
Hall effect vary the voltage drop from a power source according to the surrounding magnetic field- including the Earth's resting magnetic force. THis allows it to sense up, down, and the presence of other electro-magnetic fields.
Pros
+ Reaction is limited to the presence of a magnet
+ Magnetic field detection would serve as a basic identifying factor that would enable only individuals cognizant of the requirements of the bridge to activate it, and do so discreetly
Cons
+ Magnets + electronics = ?x??1?$?
Other unknown side effects
