Smart Audio Box (SAB) is microprocessor controlled audio switch and amplifier system, which is specifically design for audio composers and for audio engineers. SAB consist of 4 high impedance stereo inputs and two output modes. One output mode can drive stereo headphone/earphone and other output mode can drive pair of 8W speakers. In prototyping stages we identify those modes as "Personal Mode" (headphone output) and "Audience Mode" (power amplifier output).

Another main feature of this system is its programmable 16 step attenuation controller. This attenuation controller helps to control the audio output level of each output-mode.

Prototyping version of Smart Audio Box

The main component of SAB system is ATmega8 MCU, other than that headphone amplifier is design around NJM4556 high current operational amplifier and power amplifier is based on TDA1521A.

To operate, this system requires 2 power sources. Microcontroller, ADC interfaces and CMOS logic-switches requires 5V - 2A, single rail DC input. Both the output stages are design to driven by a 12V ~ 13.5V - 1.5A symmetrical power supply.

User interface of SAB system consist of 5 push buttons (S1 to S5) and 5 L.E.Ds (LED1 to LED5). S1 switch is use to toggle the output mode between power amplifier and headphone driver. S2 and S3 are profile selection switches. S4 is "manual" input channel selector and S5 is "automatic, sensor driven" input channel selector. 4 L.E.Ds are use to indicate the active input channel and remaining L.E.D indicate power status of the system.

This SAB system is design as an open hardware project. ATmega8 firmware source code is released under the terms of GNU GPL version 3.0 and all the design documents are released under the terms of GNU FDL.

Project Related Downloads

Complete source code, schematics and other design documents of Smart Audio Box (SAB).


ATmega8 - 8-bit AVR with 8KBytes In-System Programmable Flash
CD4066 - CMOS Quad Bilateral Switch
CD4052 - CMOS Differential 4-Channel Multiplexer
NJM4556AL - Dual High Current Operational Amplifier
TDA1521A - 2 x 6W Hi-Fi Audio Power Amplifier
LM358 - Low Power Dual Operational Amplifier