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.

  • \$\begingroup\$ Depending on what your application is, at that range, you might fare better with GPS. Else you're talking about fairly pricey laser distance sensors. \$\endgroup\$
    – Dr Coconut
    Commented May 2, 2015 at 8:41
  • 1
    \$\begingroup\$ What are you trying to sense? Absolute position? Relative position? Distance? \$\endgroup\$
    – David
    Commented May 2, 2015 at 8:59
  • \$\begingroup\$ To improve the way your question is dealt with I changed a certain word in your title to a more generic one. Your question is essentially independent of the processor you are using - using the title you did may have caused the question to be migrated elsewhere - and it belongs here. \$\endgroup\$
    – Russell McMahon
    Commented May 2, 2015 at 11:11
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    \$\begingroup\$ You need to provide us with a better description of what you are trying to achieve. You may wish to measure distance and/or speed but maybe colour or prettiness :-). You may be able to place a target or transponder on the target, but may be not. Th etarget may have well defined characteristics (RADAR reflectivity, optical reflectivity, ...) or not. It may be large slow and it's path well constrained (eg freight train) or fast small and elusive (eg bullet). It .............! ie tell us in as much detail as possible what you are trying to do. minimise the "how" for now. \$\endgroup\$
    – Russell McMahon
    Commented May 2, 2015 at 11:15
  • \$\begingroup\$ This question could even mean a short range sensor module on a long wire! \$\endgroup\$
    – Andy aka
    Commented May 2, 2015 at 11:17

1 Answer 1


How large is an obstruction? I think your options are probably either "build a RADAR set" (difficult, pricey) or "modify a laser rangefinder to do what you want". There exists an open source laser rangefinder base unit: http://www.lightware.co.za/shop/en/ - that $150 sounds expensive but realistically you're not likely to do it for less unless you have a really great supply of scavenged electronics and optics.


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