Ultrasonic motion sensor project

[exx]

I’m having a problem with my ultrasonic motion detector project. It seems only to detect sharp noises. I got the circuit from Kitsrus.com website. The only changes i made where the BC639 for a BC547 and the 1M Pot for a 500K variable resistor in series with 470K. So… hoping you could help me out.

 

[audioguru]

The BC639 has much less current gain than a BC547 and might not work.

 

[exx]

I m actually using the BC547 right now, but i'm still getting the same result. i 'm using a 555 timer to generate my 40KHz signal instead of the 40Khz crystal oscillator, can that be the problem.

 

[ericgibbs]

I m actually using the BC547 right now, but i'm still getting the same result. i 'm using a 555 timer to generate my 40KHz signal instead of the 40Khz crystal oscillator, can that be the problem.

hi,
The text for the project does state that the crystal will give better sensitivity.
The 555 derived 40kHz may not be stable enough.

 

[audioguru]

Which kit number? Kit #20 shows the schematic and parts list for an ultrasonic receiver but does not show the transmitter.

 

[exx]

Which kit number? Kit #20 shows the schematic and parts list for an ultrasonic receiver but does not show the transmitter.

Kit #49. I left out something important 2. i m using a 400ET/R180 instead of 400ST/R160 as in the circuit