The H-switch
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The H-switch, Hierarchial switch.  The H-switch was made in attempt to providea high level of control for a robot soccer competition to show that Beam is as good as programable robots.  The idea was this would recieve input from a number of sensors, then produce multiple behaviours that would allow the robot to play soccor.  What was done first was define soccor-playing behaviours.  The basic behaviours were suited for digital control.  Consequently the H-switch is a simplified from of a general control.  The principle is senors send signals that are pre-processed to give a set of conditions that are then sent to the control unit made completely out of H-switches, decides which behaviour to activate.  In operation a sensor trigger the signal is processed, then the H-switch activates the circut that contains the behaviour that was pre-determined by the maker that is the behaviour best suited for that situation.  The sensors and the circut are BEAMish.  The circut has two inputs and two outputs.  A high input signal indicates a sensor is sending a signal.  A high output indicates a behaviour circut should be activated.  A high (activated) Enable (En) input causes a high output.  If the Enable is low (inactive) no output is sent.  The Activate (Act) output can be used to lower the other H-switches down in the hierarchy, or it can be used as a condition.  The Activate is low when either the Enable is low, or the Output is high.  In other words the Activate signal can be passed on only if the H-switch is both enabled and not sending an output.  At the top of ther hierachy, the Enable of the topmost switch is connected to Vcc.  This mean it is permanently activated.  This switch could respond to some type of edge avoidance.  since the switch is at the top of the hiearchy, when the condition to activate it is met the Activate output goes low, which shuts off ALL other switches below it.  So the first switch is the primary concern of the robot.  The next switch activates when the first one is not active, but the conditions for the second one is met and so forth.  Note the sensor inputs can be both external and internal, the robot moniters its own condition and behaves accordingly.  Bruce Robinson said "I found that the H-switch design works better for

a team of soccor playing robots than for a single fire-extinguisher robot, even though the two types of robots I devised share a lot of physical charateristics."  This discovery was counter-intuitive, the soccorbots are in an ever changing enviroment, with more rules and more senarios than the fire-extinguishing bot with a structured enviroment that doesn't change.  For small

hiearchies like the example before the H-switch may add parts with the same effectivness.  The H-switch is useful Hiearchies I think 5 through 10 though theoretically there is no limit to the number of levels of hiearchies you can have, but the more hiearchies you have the more parts you have, more space, and more cost.  The H-switch is digital, but when connected to a BEAM circut the entire robot as a whole is still mostly BEAM.  The H-switch itself can evovle into something entirely BEAM though people will have to work with it and experiment, though I don't think many people are so it will take a while for any changes to occure. 

Here are some things that can be used to make an H-switch though some of these may not work.  You could program a  for one switch per chip, a 74HC04 (Hex inverter) and a 74HC08 (Quad AND gate) for two switches.  A 74HC04 per six gates and a 74HC08 per two switches.  74HC08 (AND), 74HC86 (XOR).