Pololu Robotics & Electronics
My account Comments or questions? About Pololu Contact Ordering information Distributors

Using custom reflectance sensor for wall following


Typically Sharp IR sensors are used to get an analog reading for the distance to a wall and in turn use PID. So, in order to try and push the boundaries and/or be different than most I had an idea and I was wondering if someone more experienced could offer some insight into the feasibility of this idea.

So, I know that the QR sensors have a max readable range of about 1/2 inch so I thought about using the same idea but with much higher wattage IR sensor/detector pairs. I was looking at using the star styled 1W dissipation LEDs shown here. For the receiver I was looking at using the component here.

So, ultimately, my question is, if I have a four inch wide robot in a twelve inch wide “hallway” would my reflectance sensor be able to give a good variance in the reading from the receivers or would the walls be too far away?

A couple of other reasons I want to do this other than being different are:
[ul]*Sharp sensors are “slow”, the best rate is 16ms per reading and I want my robot to go at least 3 ft/s
*Sharp sensors are very focused and tend to be hard to detect objects like chair legs (my receivers have 80 degree visibility[/ul]


Were you able to solve this as I’m having a similar predicament in my project. thanks


It’s been quite some time since this post so generally I wouldn’t advocate bringing it back from the dead but it was never responded to and I have some additional information to provide.

I was in fact able to do this however the max distance before seeing the wall sufficiently was about six inches. However, it’s important to note that the wall was only one inch tall. I didn’t test this method with a taller wall but I would assume it would be slightly better since you would obviously get more reflectance.

Another thing I learned from this is that using high wattage LEDs may not be feasible depending on your robot’s size, it consumes a lot of power in addition to requiring various 3W resistors which are large in and of themselves. Ultimately it was a success with a robot about 9x6" in size.

I had two 1W LEDs facing outward at about 45 degree angles and below them I had five light intensity sensors (TSL235R) and I implemented a PID algorithm and I had tweaked the Pololu QTR library to work with the TSL sensors so essentially it was almost exactly like using a pololu line sensor (from a software perspective).

I had a fun time getting this to work but I feel there are better options to go with given the power consumption and minimal distance to the short wall. For me this was merely a proof of concept so I didn’t take it much further and I didn’t look into alternatives so I can’t give much in the way of suggestions there.

The suggestions I can provide are that you limit the angle at which light comes into the sensors so you know only mostly reflected light will be coming in. Keep in mind the distance at which you need reflectance (greater than 6" is difficult with a short wall). Maybe use a lens on the LED to focus the beam, I bought some but never had time to try them out, I feel this would give better range since you can focus the beam to get higher reflectance.

That’s all for now, good luck and I’ll try to keep checking this but you may want to start your own thread once you get started.