AudioMUX Click
PID: MIKROE‐3344
Weight: 30 g
AudioMUX click is a sound processing Click board™ with digital controls,
based on the TDA7468D IC. It can be used to select one of four audio input
channels, adjust its frequency response and volume, and send it to the
output. There is also a BASS ALC section implemented on this IC, keeping
the base in control even on higher volume settings. Independent LEFT and
RIGHT channel volume, digital control over the I2C interface, a full set of
3.5mm vertical jack connectors onboard… All these features make the Click
board™ a very good solution for the development of all kinds of audio
applications.
The Click board™ is supported by the mikroSDK compliant library, which
includes functions that simplify software development. The Click board™
comes as a fully tested product, ready to be used on a system equipped with
the mikroBUS™ slot.
Featuring a set of 3.5mm vertical jack connectors onboard, it allows a simple
connection to an existing audio chain. Because of its very good sound
characteristics, including 0.01% of total harmonic distortion (THD), signal to
noise ratio (SNR) of 100dB, 84dB of maximum attenuation, and more, this
Click board™ represents an ideal solution for developing and building audio
applications that can be used for various HiFi systems, home stereo
components, computer speakers with selectable input, and many other
similar audio applications that require a digitally controlled input selection
and audio processing.
How does it work?
AudioMUX click is based around the TDA7468D IC from STMicroelectronics,
which is a two-band digitally controlled high-quality audio processor with
BASS ALC feature and a four-channel input selector. This integrated audio
processor is quite popular, and it can be found in several brands of HiFi and
home stereo systems. Despite its simplicity, it offers a full set of options
required for a realization of the four-channel audio multiplexer with volume,
balance, and tone controls. The TDA7468D IC is digitally controlled over the
I2C interface; however, the internal sections are purely analog circuits, with
a separate analog GND reference.
There are four input channels which can be selected over the I2C interface.
The IC accepts up to 2.5V peak to peak at its inputs. The impedance of the
input terminals is 50 kΩ, and each input is decoupled by a 440nF capacitor.
There are not many registers in this IC, which makes the firmware
development very easy. Each channel is routed to a vertically mounted
3.5mm jack, which allows the Click board™ to be easily interfaced to an
existing audio chain.
Some registers have a single function, while others are used to control more
functions. The datasheet of the TDA7468D clearly explains each register and
its functions.
After the input is selected by setting the specific bits in the INPUT SELECT
register, the audio signal is routed to the first gain stage. It is possible to
adjust the gain of the input signal up to +14dB, in 2dB steps. This is very
useful when the amplitude of the input signal needs to be adjusted (gain
staging)
The signal is then fed to the first (pre-EQ) volume control section which is
able to attenuate the signal down to -63dB, in 1dB steps. If the signal is too
high, a clipping might occur when the equalization is applied in the next
section. Therefore, lowering the volume in this section will allow more
headroom for the equalizer (EQ) section. The volume in this section is
determined by the first 6 bits of the volume control register, referred to as
the VOLUME 1 bitfield. The last 4 bits are related to the post EQ volume
section and are referred to as the VOLUME 2 bitfield. Both volume sections
feature independent volume control registers (VOLUME LEFT and VOLUME
RIGHT), allowing balance function to be implemented.
The EQ sections can adjust bass and treble frequencies in the range from 14dB to +14dB, in 2dB steps. The frequency response of these sections is
determined by external RC elements. The Click board™ has these values
optimally selected for the best performance. The low-frequency range is
processed by a T type bandpass filter with its center frequency at around
32Hz, while the high-frequency range is processed by a high pass filter with
the -3dB attenuation point at about 3kHz. A single register is used to control
the entire EQ section (TREBLE & BASS register).
After the sound is processed by the EQ section, there is an output stage,
which allows attenuation of -24dB in 8dB steps. This post-EQ stage allows
the volume to be fine-tuned and adjusted to the input stage of an audio
amplifier. The volume of this section is controlled by the VOLUME 2 bitfield,
in two independent registers, one for each channel (VOLUME LEFT and
VOLUME RIGHT)
The BASS ALC is a kind of a compressor which is applied to the lowfrequency range. It is a very useful feature, keeping the low-frequency
content even when the volume is set to a high value. The low-frequency
band will be dynamically attenuated when the programmed threshold value
is exceeded, after the programmed attack time. The BASS ALC is
automatically turned off when the EQ is set to attenuate low frequencies, as
there is no point to use it in that case. There are also some additional
settings for the BASS ALC function. For the complete list of features, please
refer to the datasheet of the TDA7468D. The BASS ALC function is controlled
by bits in the BASS ALC register.
The output of the TDA7468D IC can be enabled or disabled by a single
control bit of the OUTPUT register.
When building audio applications in a purely digital surround, special care
should be taken to isolate the audio signal path as much as possible, in
order to avoid any noise at the output. This Click board™ is equipped with
two 0 Ω resistors (jumpers) at strategic positions. These jumpers are labeled
as J1 and J2. They can be replaced either with resistors or with inductors. J1
jumper connects analog and digital GND in a single point. If the reference
GND is noisy, using a clean external power supply (PSU), combined with a
small resistance value up to 100 Ω in the place of J1, can help in reducing
the output noise. The second jumper (J2) can be replaced with a ferrite bead
or an inductor, which can help to filter the noise at the positive rail of the
power supply. The noise at the output can also be a result of improper gain
staging (e.g. all the gains are at their maximum value). The TDA7468D itself
is not very noisy, only about 15 µV max.
The SMD jumper labeled as VCC SEL is used to select the power supply. If
set to 5V, the TDA7468D IC will be powered from the mikroBUS™ +5V rail.
When the jumper is set to VIN, the TDA7468D IC will be power from an
external power source connected to the VIN screw terminal. The external
power source voltage should be within the 5V to 10V range.
The logic section of the TDA7468D will always be powered from the
mikroBUS™, regardless of the VCC SEL position. However, it is still possible
to select the voltage level for the I2C bus, allowing communication with a
wide range of different MCUs. This can be done by switching the SMD
jumper labeled as I/O SEL to either 3.3V or 5V.
Specifications
Type
Audio
Applications
It can be used in various HiFi systems, home stereo components,
computer speakers with selectable input, and many other similar
audio applications that require a digitally controlled input selection
and audio processing.
On-board
modules
TDA7468D IC from STMicroelectronics, a two-band digitally
controlled high-quality audio processor with BASS ALC feature and
the input selector
Key Features
High quality audio output, integrated four-channel input selector
with tone controls, each connector is a high-quality vertically
mounted 3.5mm standard stereo jack, good frequency response,
low THD and SNR, it can be directly implemented into the existing
stereo system, etc.
Interface
I2C
Input
Voltage
3.3V or 5V
Click board
size
L (57.15 x 25.4 mm)
Pinout diagram
This table shows how the pinout on AudioMUX Click corresponds to the pinout
on the mikroBUS™ socket (the latter shown in the two middle columns).
Notes
Pin
Pin
Notes
NC
1
AN
PWM
16
NC
NC
2
RST
INT
15
NC
NC
3
CS
RX
14
NC
NC
4
SCK
TX
13
NC
NC
5
MISO
SCL
12
SCL
I2C Clock
NC
6
MOSI
SDA
11
SDA
I2C Data
Power Supply
3V3
7
3.3V
5V
10
5V
Ground
GND
8
GND
GND
9
GND
Power Supply
Ground
Onboard settings and indicators
Label
Name
Default
Description
LD1
PWR
-
JP1
VCC SEL
Right
JP2
I/O SEL
Left
J1
J1
Populated
Jumper between the analog and digital GND
J2
J2
Populated
Jumper in series with the mikroBUS™ 5V power
supply rail
Power LED indicator
Power supply input selection: left position VIN
connector, right position 5V from the mikroBUS™
Logic level voltage selection: left position 3.3V,
right position 5V
Software support
We provide a library for the AudioMUX Click on our LibStock page, as well as a
demo application (example), developed using MikroElektronika compilers. The
demo can run on all the main MikroElektronika development boards.
Library Description
Library offers a choice to perform a control of the AudioMUX Click board. The
control consists of input control, output control, gain control, volume control,
treble and bass control... The device also can work in Bass ALC Mode by
using this library. For more details check the documentation.
Key functions:
T_AUDIOMUX_RETVAL audiomux_writeSingleByte( uint8_t regAddr, uint8_t dataIn
) - The function writes one-byte data to the register.
T_AUDIOMUX_RETVAL audiomux_selectInput( uint8_t inputSel, uint8_t muteIn,
uint8_t micGain, uint8_t micState ) - The function performs an input selection and
control.
T_AUDIOMUX_RETVAL audiomux_setVolume( uint8_t volume1, uint8_t volume2,
uint8_t sideSel ) - The function performs a left or right volume control.
T_AUDIOMUX_RETVAL audiomux_setTrebleBass( uint8_t treble, uint8_t bass ) - The
function performs a control of the treble and bass for EQ section.
Examples description
The application is composed of the three sections :
System Initialization - Initializes peripherals and pins.
Application Initialization - Initializes I2C interface.
Application Task - (code snippet) - Initializes AudioMUX device to work with the desired
configurations and shows a message on UART when playing is started. Device initialization will
be performed only once and after that AudioMUX will work with the same desired
configurations.
void applicationTask()
{
if (initCheck == 0)
{
audiomux_selectInput( _AUDIOMUX_IN1_EN, _AUDIOMUX_MUTE_INPUT_OFF, _AUDIOMUX_MIC_GAIN_1
4DB, _AUDIOMUX_MIC_OFF );
audiomux_setInputGain( _AUDIOMUX_IN_GAIN_2DB );
audiomux_writeSingleByte( _AUDIOMUX_SURROUND_ADDR, _AUDIOMUX_MIX_0 );
audiomux_setVolume( _AUDIOMUX_VOL1_6DB_NEG, _AUDIOMUX_VOL2_0DB, _AUDIOMUX_VOLUME_LEFT_
ADDR );
audiomux_setVolume( _AUDIOMUX_VOL1_6DB_NEG, _AUDIOMUX_VOL2_0DB, _AUDIOMUX_VOLUME_RIGHT
_ADDR );
audiomux_setTrebleBass( _AUDIOMUX_TRE_BASS_4DB_NEG, _AUDIOMUX_TRE_BASS_14DB );
audiomux_writeSingleByte( _AUDIOMUX_BASS_ALC_ADDR, _AUDIOMUX_MODE2_ADAPTIVE );
audiomux_muteOuput( _AUDIOMUX_MUTE_OUTPUT_OFF );
initCheck = 1;
mikrobus_logWrite( "Playing", _LOG_TEXT );
Delay_ms( 1000 );
}
if (messCnt
