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The SunSeeker Head
Light-Tracker

INTRODUCTION
Just in case you re new to BEAM robotics, let s go through the basics: BEAM is an acronym for the four fundamentals of building relatively simple robots. iology - Steal the best ideas that mother nature has come up with so far. Can t beat several million years of development for inspiration. lectronics - Since we can t (easily) use biochemistry to build our devices, we ll use simple, effective electronics to fulfill our needs. You will rarely find anything as complicated as a microprocessor in a BEAM robot, as we strive to get the most performance out of as little silicon as possible. You will often find a solarcell glommed onto the top of many BEAM devices, and though much less powerful than regular AA batteries, they will last for years. This gives solar-powered BEAM devices very long lifetimes where they won t require you watching over their battery status. esthetics - Just another word for Coolness . If it looks clean, lean, and slick, chances are that it was well built and will last much longer than a device lacking aesthetic appeal. echanics - Clever mechanical design of a robot can make it very effective, much more so than a clumsy design that needs additional electronics to overcome its mechanical limitations. Many BEAM robots are often built out of recycled technology , otherwise known as techno-scrap (like that broken walkman in you junk-drawer). With that out of the way, let s get onto the workings of the SunSeeker 1.0. The SunSeeker is a rotating device that analyses its environment for the brightest source of light, and then does its best to point itself at it. When the SunSeeker thinks it is aimed right at it, it blinks the LED indicators on its front. The electronic operation of the SunSeeker is based around two voltage detectors each fed by a photodiode. The photodiode is a power-generating device, and when exposed to light, it starts charging a small capacitor. This charge is monitored by a 1381 voltage detector, which sends out a signal when the charge has met a predetermined level. It is the fight between these two teams of components that cause the lightseeking behavior of the SunSeeker. When one side of the SunSeeker has more light than the other, that side obviously charges its capacitor quicker, triggering its associated 1381 first. The pulse from the 1381 runs to the 74AC139 chip, which dumps the power being stored in the big capacitor to the motor in such a way that it turns the SunSeeker body towards the light. When both 1381s reach their trigger point at about the same time and both send a signal to the 74AC139, the chip has a dilemma. Does it turn left, or right? Well, we set it up so that it dumps the power usually used to making the SunSeeker turn into blinking the LEDs instead. Besides having a pair of photodiodes as its optical detectors, the SunSeeker also has optional tactile (touch) sensors you can install so that it won t bump into objects in its way. These work by dumping extra power to the photodiode capacitor on the other side of the SunSeeker. This effectively makes the SunSeeker think that (all of a sudden) that there s a GREAT WHACKING BRIGHT STAR on the other side, making it look away from the obstacle.