I’ve designed this piezo buzzer circuit to transmit data using frequency shift keying. But I’m not an expert. Can someone take a look and let me know if it looks alright?
http://upverter.com/sdelgado/2ad26b3189fe6564/Buzzer-Transmitter/
Looks good to me.
Current circuit is fine due to impedance matching. However, adding a flyback diode would help protect the circuit from damage. Schottky diodes are recommended for their fast switching ability. Here’s one that would work.