I want to build a sensor module that has a long range.
I was going to use an ultrasonic sensor for my project where I needed to know the exact distance of an obstruction in the path of a moving body (to which the sensor is attached). But I needed a large range (because the sensor will be used in vehicles like trains) and read that ultrasonic waves won't be able to detect the obstruction at a large distance quite as well. Because they spread out, there might be some disturbances (unwanted elements being detected). So I thought I'd ask if there were alternatives to ultrasonic sensors that still have the large range.
About 500m would be optimal, but I think I can settle for anything above 100m if I have to.
Cost is a limiting factor, so it would be best if it can be frugally homebrewed or bought for a low price. Any suggestions? Thanks.