Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Polarity of sonar sensors

  1. Aug 30, 2011 #1
    Hello, for my robot project, I'm using a system of of sonar range finding sensors which are generally used for this type of thing. My question is of there polarity. I'm assuming that it does not matter, for there are no clear indicators of positive or negative values on any of the poles.
    here are the schematics I'm following.



    I don't know if this helps explain what I mean. I just need to know if there is any difference on any of the points.

  2. jcsd
  3. Aug 30, 2011 #2
    Those schematics are not for sonar, they are for an ultrasonic motion sensor. (Admittedly they might be advertised with the word "sonar" but its just to increase sales). All those schematics can do is sense motion, they can't tell you how far away anything is. Typically the output of the receiver stage is watched for changes (simplest way is to send it through a phase or amplitude detector), because any change indicates there was motion. Polarity shouldn't be an issue unless there is some really fancy signal processing after that receiver front-end, which is unlikely for those circuits (that is, if you wanted to do something fancier than simple motion detection you wouldn't use that sort of transmitter and receiver).
  4. Aug 30, 2011 #3
    Yeah, I thought sonar is a bit too big of a word for them lol. thanks for the help. that answers my question.
  5. Dec 12, 2011 #4
    You should be able to use those two devices together. You modulate a signal; when the signal hits something it should echo back. Then you should be able to match the return signal. The time it takes to get your response should tell you how far away an object lies.
  6. Dec 22, 2011 #5


    User Avatar
    Gold Member

    The links show a 40 kHZ transmitter and a 40 kHZ receiver for a sonar rangefinder system. The timer and control circuits are not shown. The transmitter emits a short pulse and when the echo is received it trips the comparator in the receiver. The control circuits measure the round-trip time between transmit time and recieve time and then calculate the range. This is exactly how a sonar rangefinder works.

    Can you please be specific: What poles are you referring to? What points are you asking about differences?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook