### Upgrading ultrasonic range finder

Posted:

**Wed Jun 11, 2014 2:00 pm**I have taken idea "Precision to the Last Micron" posted on http://blog.redpitaya.com/?p=218 and upgraded it by means of extending the distance range. First, i have obtained 40 kHz ultrasonic transducers from Farnell. I have used the same setup than the author in abovemntioned blog, but, instead of using fixed frequency of 40kHz i have created frequency sweep ranging from 39 to 41 kHz. Then i have played the sweep using the pitaya through ultrasonic transducer (tx). I have captured the delayed signal using other transducer (rx).

Then i have detected the time it took for the signal to travel from tx to rx:

I have multiplied tx and rx signals. Since sin(a)*sin(b) = 1/2(cos(a-b)-cos(a+b)) i have got signal which contained 2 spectral lines with frequency difference and frequency sum. From knowing the sweep ramp i was able to calculate the delay and from the delay and speed of sound the distance.

The setup is currently able to measure distance up to 3 m.

Then i have detected the time it took for the signal to travel from tx to rx:

I have multiplied tx and rx signals. Since sin(a)*sin(b) = 1/2(cos(a-b)-cos(a+b)) i have got signal which contained 2 spectral lines with frequency difference and frequency sum. From knowing the sweep ramp i was able to calculate the delay and from the delay and speed of sound the distance.

The setup is currently able to measure distance up to 3 m.