Automatic Gate opener Sensor problem

Discussion in 'The Projects Forum' started by RHKain, Jun 7, 2014.

  1. RHKain

    Thread Starter New Member

    May 24, 2014
    The project is an automatic gate opener (small scale)
    I'm using the circuits attached to this thread to drive the sensor to detect the presence of a car (or any object) at first the receiver and transmitter are not facing each other so when there is an object it reflects the Ultrasound wave and the receiver detects it giving a signal which is amplified and the brought through a tone decoder, and that signal is used to trigger a mono-stable timer for about 10 seconds which switches an H-bridge using relays and then closes after that time.
    Now the problem is, (other that in the transmitter circuit pin 6 and 7 i fixed that) the sensor doesn't seem to work... what could be the issue? and i triple checked the values... so can u find anything ???
    • 93.jpg
      File size:
      29.6 KB
    • 94.jpg
      File size:
      16.4 KB
  2. masosi


    Dec 23, 2007
    Did you design this circuit yourself? The reason I ask is I have seen many ultrasonic circuits online that I have tried and have failed. The reason is the difference in ultasonic transducers. There are just so many types available.

    Some transducers I have seen are very sensitive and dont really require too much amplification to get a usable signal from the receiving end. The current circuit I have designed and is working amplifies the received signal by about 60x using 3 stages of op amps just to get anything useful out of it. My transmitter is rated at 140vPeakPeak so this circuit would not work for me. I am using a matching transformer to step up my pulse voltage from 5v to 130V at 40kHz.

    So if you are just using 'any' ultrasonic transducer with this circuit, it may not be sending a large enough pulse to move the transducer or if may not amplify the response signal enough to see anything. Hook up a scope and see what is coming back. That is what was happening for me.

    (I send 4 pulses at 130Vpp 40kHz and receive a reflection of a lot of noise instantly, then a reflected signal of 20mVPP which is then amplified.)

    Hope that helps.
  3. ScottWang


    Aug 23, 2012
    The high pulse width about 9.1%, so you should measuring the output of op amp from the first stage.
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    here is an ultrasonic Rx circuit using an opamp.

    I think your circuit is from this site

    note the capacitor C2 and the input to the 2nd opamp is on pin 3.