$Id: README,v 1.9 2003/10/05 05:17:42 dwalters Exp $-- Open Automaton Project: http://oap.sourceforge.net -- HEAD CONTROL MODULE INTRODUCTION--------------------------------This README covers the source code and circuit schematics for the Open Automaton Project Head Control Module.The Head Control Module is a hardware device that controls the Pan and Tiltservomotors of the head, as well as taking passive infrared sensor readingsfrom the head-mounted Eltec infrared sensor. This device passes control and sensor readings data to and from the robot's mainboard via the I2C interface,using the SMBus protocol.The circuit schematic (head_control_module.sch) was developed in gschem, partof the gEDA package, version 20030525.Circuit schematic symbols that are not in the symbol library bundled with gEDAare included as separate sym files (these .sym files can be copied into yourlocal symbol directory, typically /usr/local/share/gEDA/sym/local/).LICENSING---------All source code and electronic circuit designs are copyright (C) 2003, Dafydd Walters.The Open Automaton Project software is distributed under the terms of the GNUGeneral Public License. See the file COPYING.SOFTWARE for details.Please see the file COPYING.ELECTRONICS to see the terms under which theelectronic circuit designs of the Open Automaton Project are distributed.CIRCUIT NOTES-------------The Eltec passive infrared human body heat sensor detects movement of heatsources along a particular axis (along the same direction as the tab on theperimiter of the detector's metal body).  It is important to mount this sensorso that it is oriented to detect movement along the same axis as the Panservo. A polyethylene freznel lens should be mounted at the appropriate distancefrom the detector to ensure that infrared energy is focused on to the detectorcorrectly (the sensor kit from Acroname includes the lens and a cut-outpattern which can be used to construct a suitable concentrating cone that holds the lens and the detector at the correct distance apart).This circuit provides power to the servos from a 7805 voltage regulator. The7805 (with a heatsink attached) can deliver up to 1A. The current consumedby the other components is negligible, so servos that draw an absolute maximum current of 490mA each should chosen for Pan and Tilt.Due to surges and spikes associated with motors, it's important to placetantalum bead supply decoupling capacitors very close to each of the Pan andTilt RC servo connectors. If you can completely separate the power supplies of the servos from the rest of the circuit, so much the better.Most servos specify a PWM period of 20ms, with an "on-time" pulse width range of 1ms to 2ms. However, this range does not allow servos to reach theirpotential maximum positions, so the Head Control Module outputs a PWM pulsewhich can be driven anywhere in the range 0.5ms to 2.5ms. This extended rangealows the servos to be driven to their end stops.  HOWEVER, you shouldestablish what the drive limits of your particular servos are, because you should never drive servos quite as far as their end stop postions. You can establish by trial and error what drive setpoint values correspond to these positions just short of the end stops, by using the oap-head utility.SMBUS INTERFACE---------------This module is a slave on the I2C SMBus, with the fixed address 88(the address can be changed by modifying the source code and re-compiling).The device responds to the following host (master) commands:Read Byte Data, Command = 1: Report Pan servo setpoint (one data byte). The                             actual driven position of the servo will                             eventually "catch up" with this value, depending                             on the value of the "Maximum Change Per Period"                             setting.Read Word Data, Command = 2: Report Pan servo actual driven position (two data                             bytes). The first data byte is the actual driven                             position of the servo, and the second is the                              current 8-bit timer count (20ms per tick).Read Byte Data, Command = 3: Report Tilt servo setpoint (one data byte). The                             actual driven position of the servo will                             eventually "catch up" with this value, depending                             on the value of the "Maximum Change Per Period"                             setting.Read Word Data, Command = 4: Report Tilt servo actual driven position (two data                             bytes). The first data byte is the actual driven                             position of the servo, and the second is the                              current 8-bit timer count (20ms per tick).Read Byte Data, Command = 5: Report "Maximum Change Per Period" setting (one                              data byte).  This is the maximum change per update                             period (which is 20ms) of the servo's driven                             position. The smaller this value is, the slower                             (and smoother) the servos will appear to respond                             to changes in setpoint. See the command 102 for                              more information on this setting.Read Byte Data, Command = 6: Report raw analog IR sensor reading (one data                             byte). This is useful only for testing (and                             establishing a suitable value for the "IR Sensor                             Neutral Value" setting). Triggered IR detections                              (see commands 9,10,12,13) should be used when                              actually sensing heat sources.Read Byte Data, Command = 7: Report the value of the "IR Sensor Neutral Value"                             setting (one data byte). This is the ADC count                              that the IR sensor is expected to hover around                             when there's no moving heat source present.Read Byte Data, Command = 8: Report the value of the "IR Sensor Trigger                             Threshold" setting (one data byte). This is the                             number of ADC counts above or below the "IR                             Sensor Neutral Value" setting that triggers a                             detection event.Read Byte Data, Command = 9: Report the value of the Pan servo actual driven                             position for the stored IR detection event (one                             data byte). Host should use command 10 first to                             check if a detection event occurred, and to                             "lock" it (i.e. prevent it from being                             overwitten by another event).Read Byte Data, Command =10: Report the IR triggered event status (one data                             byte). The data byte returned is zero if no                             event has been triggered, and one if an event                             has been triggered. When 1 is returned, this                              command has the side effect of "locking" the                              event data so that it cannot be overwritten by                              another event when the triggered event mode is                             "Last Event" or "Maximum Event" (the lock has no                             effect if the triggered event mode is "First                             Event"). The purpose of the lock is to allow all                             the characteristics of the event to be read by                             the host (using commands 9,12,13) without fear of                             another event being triggered in between the                             calls to the various commands to read the event