DIGI POT 3 click
PID: MIKROE-3016
Weight: 25 g
DIGI POT 3 click is a versatile and
feature-rich digital potentiometer click
with 1024 steps and an internal non-
volatile memory (EEMEM), which can
be used for storing the wiper position,
but also for storing various user data.
The user EEMEM area has 14 words,
each with 16bit length. The Click
board™ can be used with both
unipolar and bipolar signals,
selectable by onboard SMD jumpers.
The wiper position can be increased or
decreased linearly or by the
logarithmic scale (6db/step) with a
single command. A special scratch
register allows direct programming of
the wiper position. It can be stored to
the non-volatile memory and on the
power on, it is automatically restored.
This means that the device restores its
last position after the power on - just
like its mechanical counterpart.
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Table of contents
1. How does it work?
2. Specifications
3. Pinout diagram
4. Onboard settings and indicators
5. DIGI POT 3 click electrical
characteristics
6. Software support
7. mikroSDK
8. Downloads
DIGI POT 3 click is a versatile and feature-rich digital potentiometer click
with 1024 steps and an internal non-volatile memory (EEMEM), which can be
used for storing the wiper position, but also for storing various user data.
The user EEMEM area has 14 words, each with 16bit length. The Click
board™ can be used with both unipolar and bipolar signals, selectable by
onboard SMD jumpers. The wiper position can be increased or decreased
linearly or by the logarithmic scale (6db/step) with a single command. A
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special scratch register allows direct programming of the wiper position. It
can be stored in the non-volatile memory and on the power on, it is
automatically restored. This means that the device restores its last position
after the power on - just like its mechanical counterpart.
The main advantage of the digital potentiometers over the mechanical ones
is that they can never wear out. The wiper position can be precisely
programmed, and the wiper contact with the resistive coating can never be
compromised by the influence of dirt or moisture. Due to its low THD and
good bandwidth, it can be used for digital volume control or a precise gain
and offset adjustment. It can also be used as the LCD digital contrast
control, and generally - whenever a precise digital potentiometer is
required.
How does it work?
This Click board™ carries the AD5321, a 1024-position (10bit) digital
potentiometer with a non-volatile memory (EEMEM), from Analog Devices.
As already mentioned, this digital potentiometer has many features that
make it a superior choice over the classic, mechanical potentiometers. It
offers the solid state reliability, high precision, an additional storage non-
volatile (NV) memory cells and most importantly - it can be digitally
controlled by an MCU via the high-speed SPI interface, with its pins routed to
the mikroBUS™. Analog Devices Inc. offer several sub-types of the same IC,
but the DIGI POT 3 click uses the one labeled as AD5231BRUZ10, meaning
that it has 10KΩ of resistance between the potentiometer end-points.
One of its distinctive features is to refresh its wiper register (called RDAC in
the device datasheet) after the power on, making it possible to restore the
wiper position on power-up, just like the mechanical counterpart. The wiper
position register (RDAC) is not automatically written to the EEMEM because
this type of memory has a limited number of write cycles, which is the
limitation of the technology itself. For this reason, once the position has
been established, it can be stored to EEMEM by a command (Command 0x2 -
Store RDAC setting to EEMEM). The AD5321 IC is factory pre-programmed to
set the wiper at the middle position after the power-on, but this can be
overwritten by storing a custom position with the aforementioned
command.
Besides storing the RDAC register to the EEMEM, it is possible to store 14
more words, each 16 bits long. This EEMEM area can be used for any
purpose - lookup tables, data for other components, or system
identification information. Writing to EEMEM takes some time, during which
the AD5231 IC is non-responsive. This time is about 25ms and the end of this
operation is signaled by the RDY pin of the AD5321 IC, routed to the INT pin
of the mikroBUS™ - labeled as the RDY. When the read to, or write from
EEMEM cycle is done, this pin pulses to a LOW logic level. It is otherwise
pulled to a HIGH logic level by an on-board pull-up resistor.
For the complete list of commands and addresses, please refer to the
AD5321 datasheet. However, MikroElektronika provides a library that
contains functions compatible with the MikroElektronika compilers, which
can be used for simplified programming of the DIGI POT 3 Click. The library
also contains an example application, which demonstrates their use. This
example application can be used as a reference for custom designs.
The Click board™ is equipped with an edge screw terminals, which are used
to connect the Click board™ to the external electrical circuit. They offer a
secure connection to the external electrical circuit. A small print of a
potentiometer electrical symbol illustrates how to connect these terminals
properly: Inputs labeled as A and B are the endpoints of the digital
potentiometer, while W is the wiper. Lastly, GND symbol is for connecting
the ground of the circuit where the potentiometer will be used.
DIGI POT 3 click allows using of both unipolar and bipolar signals. The
potential across the positive and the negative power supply pins define the
boundary conditions for a proper digital potentiometer operation. Supply
signals present on the A, B, and W terminals that exceed this range are
clamped by the internal forward-biased diodes. Since this Click board™ is
intended to be used on the mikroBUS™, the power supply voltage of the
AD5321 is +3.3V or +5V, selectable by an onboard SMD jumper labeled as
VCC SEL. This makes it possible to work with the voltage range between 0
and VCC. By utilizing an additional circuitry, it is also possible to work with
the bipolar signals, which can be useful for interfacing the digipot to an
audio source.
Since there are no negative power supplies available on the mikroBUS™, the
Click board™ uses the MCP6022, a rail-to-rail, 10 MHz onboard operational
amplifier from Microchip, in order to support operation with bipolar signals.
It is used as a non-inverting amplifier with a unity gain - a buffer. There are
several onboard SMD jumpers, used to route the signal so it passes through
the buffer, instead of being fed directly to the AD5321 IC. A group of SMD
jumpers labeled as SIGNAL POLARITY is used to patch the signal to a proper
route: setting all these jumpers to the LEFT position will connect the
terminal inputs directly to the AD5231 IC, allowing unipolar signals ranging
from 0 to VCC to be connected. Moving all these jumpers to the RIGHT
position will route the input signal through the decoupling capacitor and the
buffer, allowing bipolar signals to be used, introducing an offset of VCC/2.
This allows signal to swing between VCC/2 and GND for the negative half-
cycle, and between VCC/2 and VCC for the positive half-cycle. The offset is
then removed by a decoupling capacitor at the W terminal. The SMD
jumpers should be all moved either to the LEFT or to the RIGHT position, as
leaving some of them in the opposite position than the others may render
the device unresponsive.
The AN pin can be used as an auxiliary wiper output if routing of the wiper
back to the mikroBUS™ is required. This pin can be completely
disconnected from the mikroBUS™ by moving the appropriate SMD jumper,
labeled as AN to the RIGHT position. This will not affect the presence of the
wiper output on the output terminal.
Specifications
Type Digital potentiometer
Applications
It can be used for digital volume control or a
precise gain and offset adjustment. It can also be
used as the LCD digital contrast control, and
generally - whenever a precise digital
potentiometer is required.
On-board modules
AD5321, a 1024-position digital potentiometer
with non-volatile memory (EEMEM), from Analog
Devices; MCP6022, a R2R input/output, 10 MHz
Op Amp, from Microchip.
Key Features
Accurate positioning of the wiper via the 1024
different steps, non-volatile EEPROM memory
used for recalling the wiper position and custom
data storage, simple commands for
linear/logarithmic wiper control, can accept both
bipolar and unipolar signals.
Interface Analog,SPI
Input Voltage 3.3V,5V
Click board size M (42.9 x 25.4 mm)
Pinout diagram
This table shows how the pinout on DIGI POT 3 click corresponds to the
pinout on the mikroBUS™ socket (the latter shown in the two middle
columns).
Notes Pin Pin Notes
Wiper OUT AN 1AN PWM 16 NC
NC 2RST INT 15 RDY Ready OUT
SPI Chip Select CS 3CS RX 14 NC
SPI Clock SCK 4SCK TX 13 NC
SPI Data OUT SDO 5MISO SCL 12 NC
SPI Data IN SDI 6MOSI SDA 11 NC
Power supply +3.3V 73.3V 5V 10 +5V Power supply
Ground GND 8GND GND 9GND Ground
Onboard settings and indicators
Label Name Default Description
LD1 PWR -Power LED indicator
JP5 VCC SEL Right
LED driver voltage selection:
left position 3.3V, right
position 5V
JP1 - JP3 SIGNAL POLARITY Left
Signal polarity selection: left
position unipolar, right
position bipolar
JP4 AN Left
AN pin routing selection: left
position AN pin routed to the
wiper, right position AN pin
not connected
DIGI POT 3 click electrical characteristics
Description Min Typ Max Unit
Power supply voltage (VCC) 3.3 5 5 V
Voltage at the input terminals 0 - VCC V
Software support
We provide a library for Opto 2 click on our Libstock page, as well as a demo
application (example), developed using MikroElektronika compilers. The
demo application can run on all the main MikroElektronika development
boards.
Library Description
The library performs the check procedure for the desired outputs (IN1 - IN4).
For more details check the documentation.
Key functions:
uint8_t digipot3_sendCommand( uint8_t commandByte ) - The function
executes the desired command.
uint8_t digipot3_storeEEMEM( uint8_t location_address, uint16_t
transfer_data ) - The function stores 16-bit data to the desired
EEMEM (non-volatile) memory location.
uint8_t digipot3_writeDAC( uint16_t valueDAC ) - The function writes a
10-bit value to DAC register and determines the wiper position.
void digipot3_readDAC( uint16_t *dataOut ) - The function reads a 10-bit
value from DAC register (wiper position).
Examples Description
The demo application is composed of three sections:
System Initialization - Initializes peripherals and pins.
Application Initialization - Initializes SPI driver and restores the wiper position
value from EEMEM (non-volatile) memory to the DAC register, if this value does
not already exist in the DAC register.
Application Task - (code snippet) - Increments the wiper position by 6dB every 2
seconds. When wiper position reaches the desired value (0x0200), then the
wiper position be decremented by 6dB every 2 seconds, until position value
reaches the new desired value (0x0002). After that, the new position value will
be stored in the EEMEM memory, if that value does not already exist in the
EEMEM memory.
void applicationTask()
{
while (digitalValue < 0x0200)
{
digipot3_sendCommand( _DIGIPOT3_INCREMENT_RDAC_6DB_COMM );
digipot3_readDAC( &digitalValue );
WordToStr( digitalValue, text );
mikrobus_logWrite( "DAC value is: ", _LOG_TEXT );
mikrobus_logWrite( text, _LOG_LINE );
Delay_ms( 2000 );
}
while (digitalValue > 0x0002)
{
digipot3_sendCommand( _DIGIPOT3_DECREMENT_RDAC_6DB_COMM );
digipot3_readDAC( &digitalValue );
WordToStr( digitalValue, text );
mikrobus_logWrite( "DAC value is: ", _LOG_TEXT );
mikrobus_logWrite( text, _LOG_LINE );
Delay_ms( 2000 );
}
if (eememValue != digitalValue)
{
digipot3_sendCommand( _DIGIPOT3_STORE_RDAC_TO_EEMEM_COMM );
eememValue = digitalValue;
}
}
The full application code, and ready to use projects can be found on our
Libstock page.
mikroE Libraries used in the example:
Conversions
SPI
UART
Additional notes and information
Depending on the development board you are using, you may need USB
UART click, USB UART 2 click or RS232 click to connect to your PC, for
development systems with no UART to USB interface available on the board.
The terminal available in all MikroElektronika compilers, or any other
terminal application of your choice, can be used to read the message.
mikroSDK
This click board is supported by mikroSDK - MikroElektronika Software
Development Kit. To ensure proper operation of mikroSDK compliant click
board demo applications, mikroSDK should be downloaded from the
LibStock and installed for the compiler you are using.
For more information about mikroSDK, visit the official page.
Downloads
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mikroBUS™ Standard specification
LibStock: mikroSDK
AD5231 datasheet
DIGI POT 3 click schematic
Libstock: DIGI POT 3 click library
DIGI POT 3 click: 2D and 3D files
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