$Id: README,v 1.8 2003/09/30 23:34:36 dwalters Exp $
-- Open Automaton Project: http://oap.sourceforge.net --
SONAR ARRAY MODULE INTRODUCTION
-------------------------------
This README covers the source code and circuit schematics for the Open
Automaton Project Sonar Array Module.
The Sonar Array Module is a hardware device that manages the scanning of range
measurements from an array of SRF04 sonar sensors around the robot, passing
range and configuration data to and from the robot's mainboard via the
I2C interface. This module can monitor up to 16 sonar sensors.
The circuit schematic (sonar_array_module.sch) was developed in gschem, part of
the gEDA package, version 20030525.
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.
OPERATION NOTES
---------------
This module can drive up to 16 SRF04 sensors, but the number of sensors set
by host command 100 (see SMBus interface descritption below), MUST be
an EVEN NUMBER between 2 and 16, even if there are an odd number of sensors
actually in use. This restriction is necessary because of the way the module
alternates between sonar sensors that drive the two capture inputs (CCP1 and
CCP2) of the PICmicro at 25ms intervals. Note that this restriction is not
currently enforced in the firmware, but if the host does not adhere to it when
setting the number of sensors with command 100, the resulting echo readings
will be unpredictable.
Example:
Let's say you actually have 3 sonar sensors. These should be hooked up to
channels 1 through 3, and the host should set the number of sensors to 4.
When the host reads the sensors, commands 1 through 3 will return true sonar
echo return times, and command 4 will always return a zero echo return time.
SMBUS INTERFACE
---------------
This module is a slave on the I2C SMBus, with the fixed address 87
(the address can be changed by modifying the source code and re-compiling).
The device responds to the following host (master) commands:
Block Read, Command = 1 to 16: Report the latest sonar reading and timer
count for a given channel. 3 data bytes are
transferred. The first two are the 16-bit
sonar ping return time in microseconds, and
the third byte is the 8-bit timer tick count
at the time that sonar reading was taken.
The sonar readings are sent low data byte
first. The timer tick count is in multiples of
25 milliseconds. Since it is an 8-bit
value, it wraps around every 6.4 seconds.
If the sonar power is off, zero readings are
returned for both distance and timer count.
Zero readings for distance only are returned
when no sonar echo was detected at all for the
channel.
Read Byte Data, Command = 17: Read the number of sonars (set by command 100).
One data byte returned, an even number in the
range 2 to 16.
Read Byte Data, Command = 18: Read power state. 0 = sonars powered down,
1 = sonars powered up. Commands 102 and 103
set this value. The sonar array is powered
down after reset.
Write Byte Data, Command = 100: Set number of sonars (one data byte). This has
to be an EVEN NUMBER between 2 and 16. Module
stores this value in nonvolatile EEPROM.
Send Byte, Command = 101: Zero the 8-bit timer counter. No data bytes.
Send Byte, Command = 102: Power up the sonar array.
Send Byte, Command = 103: Power down the sonar array (low power mode).
This is useful to conserve battery life when
the robot is not moving. This is the default
state when the Sonar Array Module is reset.
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 PIC16F876 device, type
gpasm -n sonar_array_module.asm
The resulting hex file will be called sonar_array_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 Sonar Array Module
requires the following configuration bit settings:
- Flash program memory code protection: Off
- In-circuit debugger mode: disabled (RB6 and RB7 are I/O)
- Flash program memory write enable: Off
- Data EE memory code protection: Off
- Low voltage programming: Off (RB3 is I/O)
- Brown-out reset enable bit: Enabled
- Power-up timer enabled: On
- Watchdog timer: Off
- Oscillator: XT (crystal)
The above configuration settings are represented by the configuration word
3D71 in hexadecimal.