TableBot Challenge: Sensor selection for table edge detection?

WBA Consulting

I have been reviewing the setups needed for the Robogames Tablebot Challenge and from that I am looking for a way to add sensors to the front of my "candidate" to give it eyes to the table surface. I simply want a ON or OFF state sensor depending on if it detects the table when then sensor is mounted from 0.5-2" from the table surface. Basically, if it sees the table, I would like an "OFF" or Low output. When the table is not seen (when it is looking over the edge to the floor), it would present an "ON" or high output. If the outputs are opposite, I can correct them easily with a couple added parts.

From looking around at various options, these look like the best option: QTR-L-1A Reflectance Sensor (2-Pack)

But, I am also looking at Parallax's QTI sensor, 555-27401, and the plethora of options for Sharp's "hobbyist standard" IR sensor. However, both of those are more expensive and one of my goals is to keep cost down in case I want to sell kits of my design.

INPUT????

Martin_H

I use the Pololu sensors frequently as they are surface mount and fit in tight spaces. I think they will work well for edge detection. They also have a set with a built in capacitor to allow for RC time to avoid the need for an ADC or comparator. I've found that RC time is good for line following, but bad for edge detection. The reason is that the response time of RC decay is a bit variable and I've had a robot drive off the edge a few times.

John Abshier

I have successfully used the Pololu RC sensors for detecting a table and also for line following.

John Abshier

WBA Consulting

Thanks for the replies. I will move forward with the QTR-L-1A sensors from Pololu.