well i was thinking of dtmf so that way i dont need to worry so much about filters, and random noise triggers, i just heard that it was ok as long as you matched the clocks, maybe from 3 mhz to 40mhz IS too much , i figure faster is better since i would do just a few pulses every few seconds, enough time for the device to receive the ping, id even be happy with a cricket sound, i dont think i want to use ultrasound since the waves are linear, and to just detect range by how loud it is, after differentiating the direction
i was hopeing to use piezo, since they are small cheap and light,
https://www.ebay.ca/itm/15-20mm-BRA...551?pt=LH_DefaultDomain_0&hash=item1c27f77ebf
but i looks like those are specific to a 6khz band, which may not work?
as for range and size i always like simple solutions, already packaged ic's if i can, they dont need to go far, nothing more than a bluetooth would, say 50-100 ft,
it could to help cut a step out if i could triangulate on a bluetooth signal itself, but like i was told, rf travels too fast to capture,