ultrasonic motion sensor help!

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legolaslee

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Hi guys. i need help for building an ultrasonic motion sensor. There must be a buzzer and LED light up when any movement is detected by the sensor. So I'm wondering if there is any reference circuit that i can refer to.
 
I would suggest using a crystal is a bad idea, range is highly dependent on the transmit frequency been accurately the same as the two transducers, which should be matched pairs as well. By using an RC oscillator you can adjust the frequency to match that of the transducers. Using a crystal will be more stable, but it's almost certainly going to be stable at the wrong frequency.
 
Oh. So can i just take out the crystal and don't replace with anything? and use the oscillator to adjust to 40kHz?
 
ericgibbs said:
Basically they are the same, except the K20 uses a crystal for stability, thats the one I would choose, if pushed.
Click to expand...

I think both designs use crystals.

The Poptronix circuit is available in kit form kitsrus.com and their distributors as "Kit 49". The description of the kit reads:

"Our first ultrasonic movement detector - Kit 20 - has been very popular. This is another circuit design which we believe is more sensitive with fewer components. The transducers are mounted on the same PCB as the circuit"
 
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