morse through ultrasounds

Using Arduino Programming Questions
#1

Hello i am working on a project the last year now but the lack of knowledge on electronics probably creats the most of my problems. i have allready finished with the rest of my project but now i want to sent a string of 24 chars with ultrasounds from one port from my arduino mega and receive it to an other.

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i have fount this schematics over internet and i have connected trancmiter to pin 7 and receiver to pin 8

analogRead on the receiver gives me nothing. ither i am doing something wrong or i cand drive the transmiter !

first of all is something like that going to work ?
should i play with pwm of the transmiter and receiver ports while both works under 40khz ? and if yes, HOW ?
digitalRead and write or analogRead and Write ?

Please help !

#2

Ultrasonic transducers like these are highly resonant - you must drive the transmitter at (or close to) 40kHz. Likewise the received signal will be at 40kHz and analogRead() isn't fast enough to follow such a rapid waveform.

You should look into adding an AM detector circuit to the receiver to convert that 40kHz AC down to its envelop. Perhaps even a single diode would be enough?

To get PWM to 40kHz means using frequency-correct mode in the relevant timer module - perhaps easiest to use a library to handle this - perhaps there's one for ultrasonic transducers?

#3