Ultrasound for speed detection, not ranging

I need to measure walking speed of a person. I know I could use an HC-SR04 for ranging and then just do the kinematics to determine speed, but I need greater range than I can get from that sensor. I need about 50 foot range.

So, here are my thoughts. I will mount an Arduino on the person. It will emit a burst of 40kHz sound for a brief period of time, followed by a longer period of silence. On another (stationary) Arduino I will be listening for 40kHz sound. If the person is stationary the time between pulses will be a constant. If the person has moved, the signal will arrive early or late. I should be able to process how early or late it arrived and determine speed.

I believe the limiting factor for ultrasonic ranging is due to the attenuation of the echo signal. It has to fall off with the cube of the distance, plus what ever is lost at the echo point.. My approach seems to solve this.


  • Does seem feasible or not?
  • I assume that if I just use an ultrasonic transducer I will need to amplify the signal on both ends.
  • Any suggestion on how to use the HC-SR04 for this. That is, can I use one to create the signal and another one to detect it?

Thanks in advance.

Sounds feasible.

Not sure you can amplify this http://www.micropik.com/PDF/HCSR04.pdf Have to replace the "emitter" with a higher current capable part. Same for the receiver - replace with a little dish capable of more gain or similar.

Thanks for the feedback CrossRoads.

Are you saying I do not need to amplify the signal? Just hook the emiter up as astable and let her run?

No, you need to send out a stronger signal for sure. HCSR04 will only handle 15mA, for its intended 4 meter (~12 feet) range. I doubt you can put 60mA in it, so you need to find a higher power speaker. Same on the receiving end - need to find a receiver with more gain, similar to http://www.prlog.org/10220462-the-powerful-pro-bionic-spy-ear-sound-booster-pinpointed-sound-amplifier-listening-device.html maybe for bat frequencies, that's higher pitch. Maybe not 40KHz, but you get the idea. http://integraonline.com/~wolfden/dish.html