ECE 4760: Final Project

Acoustic Modem

Transmitting Data Through Sound

Kenneth Pu (

Leonardo Fagundes Luz Serrano (

"A device that transmits data wirelessly through sound."

project soundbyte

Data transmission over sound is used in many communication protocols, the most common being Dual-Tone Multi-Frequency signaling (DTMF). It is used to dial phone numbers and the frequency combinations chosen for the digits are very familiar to the general public. It was also used in early modems to request internet connections and its characteristic sound is nostalgic for many people.

However, to push the data rate to higher values, ultrasound (sound waves of frequency higher than 20 kHz), is a better choice than audible sound given that it is relatively unaffected by noise produced by human speech and, at the same time, does not disturb the user.

Nowadays, some cellphone and computer applications use ultrasound to transmit data. However the channel's characteristics, such as echo, high noise for audible range and inadequate hardware for ultrasonic range, are very difficult to handle and severely limit the data rate. Applications that use it to transmit data are usually academic. Distance and speed measurement and sonar devices are where ultrasound is most useful.

The device described on this report consists of a pair of microcontrollers assisted by analog circuitry, which transmit data to each other through sound.

When a key is pressed on the keyboard connected to the transmitter microcontroller, a corresponding sound wave is generated by the speaker. The microphone converts the sound wave to an analog electric signal, which is converted to a digital signal and interpreted by the receiver. The data is then shown on an LCD display.

The initial design would use ultrasound to transmit the information as to not disturb the user and the data would be converted back into the PS2 keyboard protocol in order the mimic the keyboard itself. That way, a computer would experience no difference between a signal received from the device and a signal from an actual keyboard. Due to unforeseen challenges, we opted for a less sophisticated design, which uses audible sound.

The idea for this project came from a lab in ECE 4760, the microcontroller design class, involving DTMF. We noticed that sound was an interesting way to transmit information and decided to create a transmitter receiver pair using this method.