Grumpy_Mike:
Which one is better the reed switch or the electronic sensor?
They are very similar in terms of range, both have a range of about 3mm max which I suspect is a lot shorter than you were thinking.
The hall effect being solid state lasts a lot longer but we are talking of many years in this sort of application even for a reed switch.I suggested a compass because the range would be greater but a lot more difficult to interpret. Basically it will be a point where the field changes rapidly and not in response to your direction of travel.
Yeah, it is shorter than what I was thinking of. For this project I want to build a simple system, such as driving the robot in a grid pattern with a closed setup course and beep when it detects a magnetic object. I am not to sure on if I can accomplished that easily with magnetic compass.
How will you drive a robot if there are a couple of magnetic object on the ground and having the robot to go trough each spot to beep without getting it to comeback to the spot that it already been? I think this will be great if I can understand the programming behind this as the robot will not have to go through a grid pattern that might take a long time to sweep the entire course.