I am looking to build an in audible beacon that can be detected by phone, like what sonicNotify has built at https://sonicnotify.com/
But I have no idea on how to start. I did play with the piezo speaker using ToneAC library, and I can generate 19 kHz - 22 kHz but the distance is very short.
How do I make an inaudible beacon like what SonicNotify did?
Kindly advice.
You need better transducers than just some random piezo "speaker".
What have you built so far?
I have tried 2 things.
I used DYP-ME007Y supersonic transducer. But this one cannot be detected by my phone, as the app that I am using which is https://play.google.com/store/apps/details?id=com.keuwl.spectrumanalyzer&hl=en can only detect up to 22kHz. And the supersonic transducer operates at about 40 kHz, and I cannot adjust this frequency to go between 19kHz - 22kHz.
I tried the PKM34EW and another small piezo speaker that has no model number. The circuit is pretty simple. I just connect the + and - pins to pin 10 and 9. Of course I tried it one at a time. Not both at the same time. But the the distance between the piezo speaker and the phone is very short. Is like you have to put it very near to the speaker for the phone to detect that inaudible frequency.
If that is the case, what transducer(s) that you recommend that can be integrated to the Arduino?
SonicNotify uses both the BLE and an inaudible sound transmitter in their beacons.
I want to achieve something like what SonicNotify does. Once the app on the phone detect an inaudible frequency, it triggers something.
You need to be accurate in your words.
Ultrasonic, not supersonic.
Inaudible implies something so quiet that you cannot hear it.
You need to see if you can look up just how high a frequency your cell phone microphone can pick up.
Piezo tweeters can go well above 20kHz, even rather cheap models.
20kHz is plenty high enough, most people can't hear about about 12kHz. TV flyback transformers used to run at 15.75kHz, I could hear it, but most people could not.
Inaudible implies something so quiet that you cannot hear it.
Inaudible just means you can't hear it. It could be to quiet (or too distant), out of the audible frequency range, or a sound can be inaudible if it's masked (drowned-out) by a louder sound.
No argument about the definition, but it still implies, to most people I think, a sound that is inaudible because it is either below the threshold of hearing, or quiet enough to be masked out by ambient sound.
Ultrasonic is a much better, more accurate word to use.