View Full Version : LDR vs IR sensor arrays for line following

04-06-2013, 03:05 PM
I am making a line following robot as a project. There are LDR based and IR diode based sensor panels exits in the market. The line color is white and the background color is back. So my robot need to identify white line on the black background. Therefore the IR sensors are best in the situation but the problem is the white line might be have dirt and also the arena open to the sun light. Therefore there is a risk of misbehavior of the IR sensor panel. Therefore I am thinking of using LDR based sensor panel. I found some info about characteristics of the LDR from http://www.resistorguide.com/photoresistor/ and found that the LDR has high latency and lower sensitivity . Can someone give some suggestions to select correct sensor panel?

04-06-2013, 03:20 PM
Use an array of IR LEDs and IR Photodiodes. CdS sensors are junk used for detecting ambient light, and not really meant for line following. There are plenty of options out there (pololu has several ready to use arrays, and the Bioloid STEM kit should contain a really nice line following array that behaves as a standard dynamixel device similar to the AX-S1). Even if a bit dirty, the white background should still reflect more light than the black lines and that relative difference between black line and lighter background is all that is needed.

04-06-2013, 07:33 PM
The IR sensors are typically mounted a few millimeters from the ground, and thus will block out most ambient light. Some dirt on the line will not affect the difference between light and dark all that much. Go with IR sensors for a line follower! The Pololu 8-way RC ones are pretty good.

04-07-2013, 02:35 AM
The pololu sensor, as most, uses a combination package of IR photoreflectors including both the led and the photodiode. If you want to make your own, it's easier to use those, even if they are very rare in DIP packages. You can use the leds to make a pulse pattern to eliminate the effect of some background lighting conditions. That is, you can sense the difference of the reflected IR when the LED is off, and when it's on, instead of just using the on value all the time. And also it can be useful to make a flexible shroud around the sensor. Thin plastic or thick cloth should work well in blocking all background light.