ultrasonic transducer polarity for proximity sensor

Discussion in 'The Projects Forum' started by NZMikeV, Jul 11, 2010.

  1. NZMikeV

    Thread Starter New Member

    Jun 18, 2010
    Hi All.
    I am currently assembling an ultrasonic-microphone, proximity-detector project supplied as a short-form kit (i.e. no instructions!). The only problem I'm having is that I'm unsure about the polarity of the ultrasonic microphones, or whether it matters. And if it does matter, I do not know which lead is positive or negative. There is no make/model number listed in the parts list so Google wasn't a great help. Is anyone able to tell me which lead is negative and positive, or whether it actually matters?

    The attached image has the schematic (sorry no values) and the two microphones that need identifying/sorting.
    I would think that the lead connecting to the outside case is '-', but I'm not going to solder based on assumptions.:D
  2. bertus


    Apr 5, 2008

    In the "manual" only is stated to mount the sensors at 2mm from the PCB.
    There is nothing on wich way around.
    I think the direction is of concern.


  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    Mike, I checked Mouser.com for ultrasonic receivers and transmitters. It appears Kobitone is an extremely common, low-cost producer. Unfortunately, its datasheets for the ultrasonic transmitters do not show the polarity for the pins. I checked several non-ultrasonic devices from Kobitone. They all used the case as com (neg). So, on a leap of faith, if a pin is connected to the case, it would follow that pin is negative too. I suspect it really doesn't matter which pin is com; however, using the pin connected to the case as com may make mounting easier. Worst case, you have a 50:50 chance of being lucky.

    Last edited: Jul 11, 2010
  4. hgmjr


    Jan 28, 2005
    You would think that a kit supplier would take special effort to denote clearly and unambiguously the polarity of a device if it were critical.

    I have a spare pair of "rose colored" glass for anyone with a need.

  5. NZMikeV

    Thread Starter New Member

    Jun 18, 2010
    Thanks for the help.

    The kit includes a generic component sheet for the lead-orientation of the transistors they generally use, plus a few other common components but nothing project-specific. I think I will run wires to a breadboard and mount the two microphones on that until I can confirm that it works. That way, I only have to remove the wires from the PCB and not resolder the two microphones if they are the wrong way around. Hopefully, If I'm consistent with the assumed polarity I shoud be fine. The schematic doesn't show specific polarity symbols for the mics but I would think that they need to be in phase to work properly. They can't be damaged by reversing them can they (like electret condensors) ?