Using LDR's to track the black line

A line follower robot works on the same principle as a light follower robot. However, instead of tracking light the LDR (Light Dependant Resistor) is used to track the black line. This is done by programming the chip connected to the LDR to differentiate the line colour and the colour of its surroundings (in our case a black line on a white background).

It is possible to use one LDR to act as the sensing device to track the line; however the buggy would not follow the line smoothly. To improve the smoothness (resolution) of the line following, more LDR’s would need to be used.

As we are limited to the number of LDR’s we can connect to our project board the group have made a decision to use 2 LDR’s in a line combination.

The diagram above shows how the buggy could follow the black line. It uses the two LDR's (S1 and S2) to navigate its way along the line in a zig zag motion. The LDR's (S1 and S2) read the intensity of the light being reflected from the track surface. So, when S1 is directly above the black line the light intensity is low making the buggy turn left. Smilarly, when S2 is directly above the black line the light intensity is low making the buggy turn right. We could include another case where neither S1 or S2 are above the black line. When this is the case both wheels would be turning at the same rate, therefore keeping the buggy moving in a forward direction.

This is the program that was used to illumate the LED when testing the effects of using the magnetic strip. This is demonstrated in the videos that will follow
-------------------------------------------------------
symbol Motor = 2
symbol LDR = 1

Main:
gosub Light
gosub Spin

goto main

Light:
if pin1 = 1 then
low 1
else pin1 = 0
high 1
endif

return

Spin:
high Motor
pause 200
low Motor

return

Sensors

Some background information on sensor design.

Line-following robots have difficulty tracking masking tape when the robot employs infrared LEDs and sensors. It seems most masking tape is to some extent transparent to infrared, thus the background "color" bleeds through and the robot can't see the line.

To avoid that problem, two pairs of ordinary photoresistors can be used. Also called photocells, they're able to see visible light in the same ranges as the human eye. So, if you can see the line, hopefully the robot can too.

Photoresistors react quite slowly however , which could hamper a robot that's driving around on a fast track.

Below an example of the sensors plus LED.

sourced from: http://www.robotroom.com

Line robots

My first blog as part of the Group E buggy team. I have addressed the area of the design of the buggy, the specific details of execution of function and also mechanical design.

The line follower is one of the self operating robot that follows a line that drawn on the floor. The basic operations of the line following are as follows:

1. Capture line position with optical sensors mounted at front end of the robot. Most use several number of photo-reflectors, and some leading use an image sensor for image processing. The line sensing procss requires high resolution and high robustness.
2. Stear robot to track the line with any stearing mechanism. This is just a servo operation.
3. Control speed according to the lane condition. Running speed is limited during passing a curve due to friction of the tire and the floor.

There are two line styles, white line on the black floor and black line on the white floor. Most adopting the first one in line width of between 15 and 25 mm.

- Mechanics

Right image shows bottom view and side view of the built line following robot. All mechanical and electrical parts are mounted on a proto board, and it also constitutes the chasis.

The line following robot is upheld in three points of two driving wheels and a free wheel. The driving wheels are made with a 7 mm dia ball bearing and a rubber tire. The free wheel is a 5 mm dia ball bearing attached loosely. To drive driving wheels, two tiny motors that are used for mobile phones, pager or any mobile equipment are used. Its shaft is pressed onto the tire with a spring plate, the output torque is transferred to the wheels.

The stearing mechanism is realized in differential drive that stear the robot by difference in rotation speed between the left wheel and the right wheel. It does not require any additional actuator, only controling the wheel speed will do.

sourced from : http://elm-chan.org

GANTT CHART

Project Brief

We are to build and test an intelligent buggy which will have two modes of operation. This mode will be selectable by the use of a switch.

The first operation is for the buggy to follow a line made from a dark magnetic strip of 20mm width. The deviations of the line will be at no more than 45 degrees.

The second operation is for the buggy to read road markings (90 degree turn left, 90 degree turn right and a T-junction) and execute the appropriate motion.

ROLE ALLOCATIONS

PROJECT MANAGER: IKHINE EHIMARE VICTOR

ELECTRONIC ENGINEER: ONWELL MOYO

PRODUCT ENGINEER: SIDHU RAJINDER

PROGRAMMER 1: NGANG ARNOLD

PROGRAMMER 2: NYAMBE ILUTE