$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 Tilt
servomotors of the head, as well as taking passive infrared sensor readings
from 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, part
of the gEDA package, version 20030525.
Circuit schematic symbols that are not in the symbol library bundled with gEDA
are included as separate sym files (these .sym files can be copied into your
local 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 GNU
General Public License. See the file COPYING.SOFTWARE for details.
Please see the file COPYING.ELECTRONICS to see the terms under which the
electronic circuit designs of the Open Automaton Project are distributed.
CIRCUIT NOTES
-------------
The Eltec passive infrared human body heat sensor detects movement of heat
sources along a particular axis (along the same direction as the tab on the
perimiter of the detector's metal body). It is important to mount this sensor
so that it is oriented to detect movement along the same axis as the Pan
servo.
A polyethylene freznel lens should be mounted at the appropriate distance
from the detector to ensure that infrared energy is focused on to the detector
correctly (the sensor kit from Acroname includes the lens and a cut-out
pattern 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. The
7805 (with a heatsink attached) can deliver up to 1A. The current consumed
by 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 place
tantalum bead supply decoupling capacitors very close to each of the Pan and
Tilt 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 their
potential maximum positions, so the Head Control Module outputs a PWM pulse
which can be driven anywhere in the range 0.5ms to 2.5ms. This extended range
alows the servos to be driven to their end stops. HOWEVER, you should
establish 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
characteristics. Command 105 releases the lock and
discards the stored event (command 10 would
return zero immediately after command 105 is
issued).
Read Byte Data, Command =11: Report the "IR Triggered Event Mode" setting (one
data byte). 1 = First Event (stop storing events
after the first one is triggered), 2 = Last Event
(overwrite the stored event each time one is
detected, so that the most recent event is always
the one that's stored), and 3 = Maximum Event
(only overwrite the stored event if an event is
detected with a bigger detection spike than the
stored event). 0 = IR sensing completely disabled.
Read Byte Data, Command =12: Report the IR triggered event ADC bitcount (one
data bye). 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 =13: Report the 8-bit timer value at the time the
stored IR event was triggered (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 =14: Report the current 8-bit timer value (one data
byte). This is a free running counter that
increments by one every 20ms (the servo drive
period), so it wraps around every 5.12 seconds.
Read Byte Date, Command =15: Report the status of the PWM outputs.
0 = outputs disabled (servos limp). This is the
initial default, low power mode. In this mode,
the free running timer counter and the infrared
sensing is also disabled.
1 = PWM output active (timer counter and infrared
sensing also enabled).
Write Byte Data, Command = 100 : Set the Pan servo position setpoint (one data
byte).
Write Byte Data, Command = 101 : Set the Tilt servo position setpoint (one data
byte).
Write Byte Data, Command = 102 : Set the "Maximum Change Per Period" setting
(one data byte). This is the maximum change
per update period (which is 20ms) of a
servo's driven position. The smaller this
value is, the slower (and smoother) the
servos will appear to respond to changes in
setpoint. For example, a value of 1
means that a servo's actual driven position can
only change by a maximum of 1 count per period.
Since the maximum range of driven position is
expressed as a 1 byte value (0 to 255), the time
it would take to pan from one stop to the other
is [20ms x 256], which is just over 5 seconds. A
setting value of 2 would halve that time. If you
want to get meaningful Pan position data from the
IR sensor triggered detections, this setting
should be low enough to ensure that the loaded
servos can keep up with driven positions.
Another advantage of driving the servos in this
way is that the smoother motion will put less
stress on the servos' gears and bearings,
prolonging their life. If you're not interested in
the IR sensor data and you just want the servos to
move to a new setpoint position as fast as
possible, use 255 as the value for this setting.
This configuration setting is stored in
nonvolatile EEPROM.
Write Byte Data, Command = 103 : Set the "IR Sensor Neutral Value" setting
(one data byte). This configuration setting
is stored in nonvolatile EEPROM.
Write Byte Data, Command = 104 : Set the "IR Sensor Trigger Threshold" setting
(one data byte). This configuration setting
is stored in nonvolatile EEPROM.
Send Byte, Command = 105 : Reset the IR triggered event (no data bytes).
Write Byte Data, Command = 106 : Set the "IR Triggered Event Mode" setting
(one data byte). 1 = First Event (stop storing
events after the first one is triggered),
2 = Last Event (overwrite the stored event
each time one is detected, so that the most
recent event is always the one that's stored),
and 3 = Maximum Event (only overwrite the
stored event if an event is detected with a
bigger detection spike than the stored event).
0 = IR sensing completely disabled. This
configuration setting is stored in nonvolatile
EEPROM.
Send Byte, Command = 107 : Reset the 8-bit timer counter (no data bytes).
Send Byte, Command = 108 : Activate PWM Output. Also enables the free
running timer counter and infrared sensing.
Send Byte, Command = 109 : Disable PWM Output. In this low power mode,
the free running timer counter and the
infrared sensing are also disabled. This is
the initial default mode of the module.
PEC (Packet Error Checking) is disabled for all SMBus commands.
FIRMWARE NOTES
--------------
The software for the PICMicro is written in assembly language, and compiles
using the GNU PIC Assembler, gpasm. To compile the source code into a hex file
suitable for programming a PIC16F819 device, type
gpasm -n head_control_module.asm
The resulting hex file will be called head_control_module.hex The -n option
puts DOS-style CR-LF newline sequences in the .hex file, required by most
device programmers.
It also compiles with the MPASM compiler for Microsoft Windows that is a part
of the MPLAB suite from Microchip. However, you must make sure the assembly
(.asm) file is in Windows/DOS format (i.e. with CR-LF sequences at the end of
each line) before it will successfully compile in MPASM for Windows.
Some device programmers require the configuration bits to be set manually. It
is very important that these are set correctly. The Head Control Module
requires the following configuration bit settings:
- Flash Code Protection off
- CCP1 on RB3
- In-circuit Debugger disabled
- Flash write enable off
- EE Code Protection off
- Low Voltage Programming Enable off, RB3 is I/O
- Brown-out Reset Enable on
- RA5/MCLR pin function is digital I/O
- Power-Up Timer on
- Watchdog Timer off
- Oscillator: INTRC, port I/O function of RA6 and RA7
The above configuration settings are represented by the configuration word
2F50 in hexadecimal.