Mindboards

Is there, either somewhere on the internet or in one of your houses or anywhere, really, plans for a distance sensor for the RCX? I'm trying to make a robot that scans the area around it, measuring the distance from it to where ever the distance sensor is pointing, and then looks for significantly shorter distances and steers away from them. How can I measure distance?

Do you want it to be ultrasonic, or IR? Philo wrote a nice tutorial about one that he made, based on a SHARP IR distance sensor.

techno-stuff sells some custom RCX sensors.

I was thinking ultrasonic because I'd like to have consistent readings in any light. Another thing with an IR sensor is that it'd give you a higher reading with a more reflective surface, telling the RCX that it's closer to a wall than it actually is, which could very well lead the robot to do something it shouldn't.

Yes there are some disadvantages to IR, but there are some with ultrasonic as well.

Ultrasonic needs to bounce off of a sound reflective surface (like a wall or book, not a pillow).
Ultrasonic needs to be able to hear it's echo. It needs to be fairly direct (not much angle from the surface).
You also need to be careful not to have multiple ultrasonic sensors in the same area, otherwise they will hear each other and get confused.

As far as lighting, the SHARP IR sensors are really good about that (in my experience). It doesn't seem to make a difference if the room is totally dark, or if it's well lit.
Normally you would also need to be concerned about cross talk between IR distance sensors as well, but I've heard that SHARP did an outstanding job of eliminating that (I only have one, so I wouldn't know from personal experience).
IR also seems to be faster than ultrasonic (higher update rate).

I guess there are pros and cons to each method, so you'll need to decide what is best for your situation.

Cross talk won't be an issue either way, as I'd only have one of these distance sensors. I'll try the SHARP IR one, simply because you linked to it and it's less effort to find, and we'll see what happens.

thecallosan wrote:Cross talk won't be an issue either way, as I'd only have one of these distance sensors. I'll try the SHARP IR one, simply because you linked to it and it's less effort to find, and we'll see what happens.

You won't be disappointed. The Sharp IR sensor is brilliant IMHO,

I would suggest you contact http://www.hitechnic.com/ and see if they have any of their old RCX sensors left. I was always very happy with how their ultrasonic sensor worked.

Steve

I once was using several Sharp GP2D12 sensors for the RCX.
as the Sharp sensors produce an output voltage change depending of the distance reading I used a transistor amplifier to switch a relais which was conducted to the RCX inputs. The transistor amplifier had a small potentiometer to adjust the sensitivity.
Well, it worked very well.