Fire Bird V ATMEGA2560 Hardware Manual
* In System programming and Multi-processor communication between master and salve
microcontroller
MOSI, MISO, SCK and SS pins of ATMEGA2560 (master microcontroller) are connected to the
ISP (In System programming) port as well as the SPI bus of ATMEGA8 (slave microcontroller).
Hence to do ISP you need to disconnect jumper J4 on the microcontroller adaptor board. To
access data from the slave microcontroller ATMEGA8 over SPI bus Jumper J4 on the
microcontroller socket needs to be connected.
White Line sensor calibration
By using trimming potentiometers located on the top center of the main board, line sensors can
be calibrated for optimal performance. Line sensors are factory calibrated for optimal
performance. Using these potentiometers we can adjust the intensity of the red LEDs of the white
line sensor. Sensitivity adjustment is needed, when color contrast between the white and non-
white surface in a white line grid is not adequate. In such cases the sensors can be tuned to give
maximum difference between white and non white surfaces. You can also turn on and turn off
red LEDs and take sensor readings at the same place and nullify the effect of the ambient light.
Robot comes with a flex stripe printed white line. You can use it to calibrrate robots white line
sensors by putting them on blace and white sensors.
Effect of ambient light on the white line sensors
White line sensors are highly directional in nature hence they are immune to the illumination
from tube light or CFL. Note that tube light which uses simple inductive chock actually blinks 50
times a second and this blink is captured by the white line sensors as ADC can acquire data at
very fast rates. Hence it is recommended that use CFL lights or tube lights with electronic chock
or ballast. These tube lights are the one which turns on like a bulb without flickering.
White line sensors are essentially sensitive photo transistors with precision lens assembly. All the
photo diodes and photo transistors are many times sensitive to infrared than to red light. Hence
for consistent result avoid room which have large windows even if they have curtains. Also
avoid using robots in area illuminated with filament based bulbs as they have large infrared light
radiation
Why red LEDs are used instead of IR LEDs in the white line sensors?
Photo transistors are many times sensitive to IR than to visible light but we still use red light
illumination because of following reasons:
•
Red light is nearer to the infrared
•
Since we can see red light its easier to calibrate it using eyes
•
Any color appears black because it does not reflect visible light. Which means black
surface can be ultraviolet or infrared in color. If black is infrared color then robot's white
line sensors will not be able to distinguish between white and black as black will reflect
all infrared waves as effectively as white surface. In case of red illumination which has
very less infrared radiation even infrared black is still considered as black which makes
red light as color of choice.
© NEX Robotics Pvt. Ltd. and ERTS Lab, CSE, IIT Bombay, INDIA 53