Above you can see the transmitter part of my acoustic modem. From left to right, the components are: the power supply, the acoustic transducer, the amplifier, and the microcontroller.
The problem: I need to send a 40 kHz, 20 V peak-to-peak square wave to the transducer. The circuit has two outputs, + and -, that are connected to the two transducer pins. In other words, each output needs to switch from +10 V to -10 V and back once every 25 microseconds.
As always, there are a few decent solutions, and as always I didn’t implement the best one.
I mentioned before that I’m basing my acoustic transducer off the Devantech SRF04 ultrasonic ranger. I’m removing the piezoelectric transducers from a dead SRF04 unit and using them for my modem. The transducers, which are the part that generate and receive the acoustic pressure wave that carries data, have a range of about 6 metres or so (one way), are driven with up to 20 V, and resonate at around 40 kHz.
The puzzle I’m working on right now is how best to actuate the transducer to generate a 40 kHz pulse. The SRF04 does it using a chip that’s intended to convert 5 V logic signals into the ±12 V signals used for the RS-232 serial protocol. Unfortunately most RS-232 converter chips aren’t made to power an acoustic transducer, and they aren’t able to provide enough current to generate a strong signal.