Ultrasonic motion detector project

Discussion in 'The Projects Forum' started by exx, Mar 13, 2010.

  1. exx

    Thread Starter New Member

    Mar 13, 2010
    I m using the schematics from http://kitrus.com/projects/k49.pdf to build my receiver and i m using a 555 timer to drive the transmitter at 40KHz instead of the crystal oscillator circuit. Thing is my receiver is only sensitive to loud/sharp noises, even if the transmitter is not ON. the only changes to the receiver circuit is a BC547 in place of the BC639 and 1N4007 for the 1n4002/4. So... i need help, wat do u guyz think is wrong
  2. jpanhalt


    Jan 18, 2008
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    I think your spell checker may be broken! ;)


    Did you make sure that your pinouts are not reversed on the NPNs?

    And what are you using to power the receiver? and are you scoping your input?
  4. jpanhalt


    Jan 18, 2008
    I don't understand the question. You cannot hear 40KHz, and the receiver is tuned to that frequency. How do you know what signal it is getting. A loud bang or "sharp" noise may well have frequencies in the 40KHz range and that is what you are detecting. But, you don't know how intense those sounds are.

    Does your detector work with reflected sound as it is intended to do? Is your 555 oscillator tuned to the right frequency for the detector?

  5. retched

    AAC Fanatic!

    Dec 5, 2009
    I have to agree, im not completely understanding either. Without some serious stability with power source and some 1% resistors, I cant imagine you being able to keep the oscillator at 40kHz. If it is responding to "wood-block claps" type sounds, your OSC is most likely off.

    Again, are you using a frequency counter or 'scope for your calibration?

    Reading the PDF, kitsRus seem pretty firm on power supply and crystal accuracy due to the sensitivity of the receiver.
  6. Wendy


    Mar 24, 2008
    I remember a Popular Electronics article several decades ago that sent a high frequency tone (say 22Khz) and could detect movement from the doppler frequencies. I've even seen partial schematics from the article on this site. It was considerably simpler than this schematic.

    It used something very similar to an AM radio demodulator, and then some low pass filters with high gain to pick up movement.
  7. BMorse

    AAC Fanatic!

    Sep 26, 2009
    I had made something similar quite a few years ago, It used a MX232 to drive the transducer at 16V when it sent the 8 Cycle 40Khz pulse, this enabled the transducer to "put" out a much more powerful "ping" to locate smaller objects....

    Check it out here >> http://www.robot-electronics.co.uk/htm/srf04tech.htm << it includes schematic, source and ready to program hex file...

    B. Morse
  8. Audioguru


    Dec 20, 2007
    The lousy old LM324 quad opamp is noisy and is so slow that it has hardly any gain (about 12 max) and hardly any output swing (about 3V p-p max) at 40kHz.
    I would use an MC34074 that has a 40kHz gain of about 120 and an output swing of nearly the supply voltage. It also works from a supply as low as 5V.

    The kit does not use slow 50Hz rectifier diodes. It uses 1N4148 fast diodes.

    The BC639 transistor is for up to 1A but your BC547 is for up to only 100mA but the base current is so low that both might work.