(:source http://github.com/arduino/Arduino/raw/master/libraries/SPI/examples/DigitalPotControl/DigitalPotControl.ino lang=arduino tabwidth=4:)

original tutorial by Heather Dewey-Hagborg, update by Tom Igoe and Christian Cerrito

'''original tutorial by Heather Dewey-Hagborg, update by Tom Igoe and Christian Cerrito'''

• Arduino SPI LIbrary
• BarometricPressureSensor

Examples > SPI LIbrary

explanation of SPI see the SPI EEPROM tutorial.

Controlling a Digital Potentiometer Using SPI

(:source http://github.com/arduino/Arduino/raw/master/libraries/SPI/examples/DigitalPotControl/DigitalPotControl.pde lang=arduino tabwidth=4:)

image developed using Fritzing. For

Fritzing project page

Fritzing project page-]

Schematic

Schematic

Click for for the AD5206's datasheet.

lang=arduino tabwidth=4:)

Controlling a Digital Potentiometer Using SPI

In this tutorial you will learn how to control the AD5206 digital potentiometer using Serial Peripheral Interface (SPI). For an explanation of SPI see the SPI EEPROM tutorial. Digital potentiometers are useful when you need to vary the resistance in a circuit electronically rather than by hand. Example applications include LED dimming, audio signal conditioning and tone generation. In this example we will use a six channel digital potentiometer to control the brightness of six LEDs. The steps we will cover for implementing SPI communication can be modified for use with most other SPI devices.

[[http://datasheet.octopart.com/AD5206BRU10-Analog-Devices-datasheet-8405.pdf | Click for for the AD5206's datasheet.]]

The AD5206 is a 6 channel digital potentiometer. This means it has six variable resistors (potentiometers) built in for individual electronic control. There are three pins on the chip for each of the six internal variable resistors, and they can be interfaced with just as you would use a mechanical potentiometer. The individual variable resistor pins are labeled Ax, Bx and Wx, ie. A1, B1 and W1. For example, in this tutorial we will be using each variable resistor as a voltage divider by pulling one side pin (pin B) high, pulling another side pin (pin A) low and taking the variable voltage output of the center pin (Wiper). In this case, the AD5206 provides a maximum resistance of 10K ohms, delivered in 255 steps (255 being the max, 0 being the least).

[-image developed using Fritzing. For more circuit examples, see the Fritzing project page -]

(:source http://github.com/arduino/Arduino/raw/master/libraries/SPI/examples/DigitalPotControl/DigitalPotControl.pde border=0:)

''original tutorial by Heather Dewey-Hagborg, update by Tom Igoe and Christian Cerrito''

In this case, the AD5206 provides a maximum resistance of 10K ohms, delivered in 255 steps (255 being the max, 0 being the least).

Click for for the AD5206's datasheet.

Controlling a Digital Potentiometer Using SPI

Introduction to the AD5206 Digital Potentiometer

Controlling a Digital Potentiometer Using SPI

Code

""Code""

original tutorial by Heather Dewey-Hagborg, update by Tom Igoe and Christian Cerrito

• 6 220 ohm resistors

In this tutorial you will learn how to control the AD5206 digital potentiometer using Serial Peripheral Interface (SPI). For an explanation of SPI see the SPI EEPROM tutorial. Digital potentiometers are useful when you need to vary the resistance in a circuit electronically rather than by hand. Example applications include LED dimming, audio signal conditioning and tone generation. In this example we will use a six channel digital potentiometer to control the brightness of six LEDs. The steps we will cover for implementing SPI communication can be modified for use with most other SPI devices.

(:source http://github.com/arduino/Arduino/raw/master/libraries/SPI/examples/DigitalPotControl/DigitalPotControl.pde lang=arduino tabwidth=4:)

(:div class=BOM :)

Hardware Required

(:divend:)

Circuit

(:div class=circuit :)

image developed using Fritzing. For more circuit examples, see the Fritzing project page

(:divend:)

Schematic

(:div class=circuit :)

(:divend:)

Describe what's going on here

(:div class=code :) (:source http://github.com/arduino/Arduino/raw/master/libraries/SPI/examples/BarometricPressureSensor/BarometricPressureSensor.pde lang=arduino tabwidth=4:) (:divend:)

See Also:

original tutorial by Heather Dewey-Hagborg, update by Tom Igoe and Cristian Cerrito

LED video

@]

code, tutorial and photos by Heather Dewey-Hagborg

Materials Needed:

• AD5206 Digital Potentiometer
• Arduino Microcontroller Module
• 6 Light Emitting Diodes (LEDs)
• Hookup Wire

VIDEO ? LEDs

The write_pot function allows us to control the individual potentiometers. We set the SLAVESELECT line low to enable the device. Then we transfer the address byte followed by the resistance value byte. Finally, we set the SLAVSELECT line high again to release the chip and signal the end of our data transfer.

  spi_transfer(address);
  spi_transfer(value);

  spi_transfer(address);
  spi_transfer(value);

The AD5206 is a 6 channel digital potentiometer. This means it has six variable resistors (potentiometers) built in for individual electronic control. There are three pins on the chip for each of the six internal variable resistors, and they can be interfaced with just as you would use a mechanical potentiometer. The individual variable resistor pins are labeled Ax, Bx and Wx, ie. A1, B1 and W1.

In our main loop we iterate through each resistance value (0-255) for each potentiometer address (0-5). We pause for 10 milliseconds each iteration to make the steps visible. This causes the LEDs to sequentially flash on brightly and then fade out slowly:

void loop()

     write_pot(pot,resistance);
     delay(10);
     resistance++;
     if (resistance==255)
     {
       pot++;
     }
     if (pot==6)
     {
       pot=0;
     }

@]

The spi_transfer function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found here. It then returns any data that has been shifted in to the data register by the EEPROM:

char spi_transfer(volatile char data)
{
  SPDR = data;                    // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  return SPDR;                    // return the received byte
}

The write_pot function allows us to control the individual potentiometers. First we shift the potentiometer address 8 bits to the left to put it in the most significant bit position of the 11 bit data byte. This makes room to add the resistance value which occupies the least significant eight bits of the data byte. When we sum the two together we get our 11 bit opcode to transmit:

byte write_pot(int address, int value)
{
  int opcode=0;
  address<<=8; //shift pot address 8 left, ie. 101 = 10100000000
  opcode = address+value; //10111111111

We set the SLAVESELECT line low to enable the device. Then we transfer the 11 bit opcode in two bytes sending the eight most significant bits first and sending the three least significant bits last. We set the SLAVSELECT line high again to release the chip and signal the end of our data transfer.

  digitalWrite(SLAVESELECT,LOW);
  //2 byte opcode
  spi_transfer((char)(opcode>>8));   //send MSByte address first a0a1a2d0d1d2d3d4
  spi_transfer((char)(opcode));      //send LSByte address, d5d6d700000
  digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
}

For easy copy and pasting the full program text of this tutorial is below:

[@

1. define DATAOUT 11//MOSI
2. define DATAIN 12//MISO - not used, but part of builtin SPI
3. define SPICLOCK 13//sck
4. define SLAVESELECT 10//ss

byte pot=0; byte resistance=0;

char spi_transfer(volatile char data) {

  SPDR = data;                    // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  return SPDR;                    // return the received byte

}

void setup() {

  byte i;
  byte clr;
  pinMode(DATAOUT, OUTPUT);
  pinMode(DATAIN, INPUT);
  pinMode(SPICLOCK,OUTPUT);
  pinMode(SLAVESELECT,OUTPUT);
  digitalWrite(SLAVESELECT,HIGH); //disable device
  // SPCR = 01010000
  //interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
  //sample on leading edge of clk,system clock/4 (fastest)
  SPCR = (1<<SPE)|(1<<MSTR);
  clr=SPSR;
  clr=SPDR;
  delay(10);
  for (i=0;i<6;i++)
  {
    write_pot(i,255);
  }

}

byte write_pot(int address, int value) {

  int opcode=0;
  address<<=8; //shift pot address 8 left, ie. 101 = 10100000000
  opcode = address+value; //10111111111
  digitalWrite(SLAVESELECT,LOW);
  //2 byte opcode
  spi_transfer((char)(opcode>>8));   //send MSByte address first a0a1a2d0d1d2d3d4
  spi_transfer((char)(opcode));      //send LSByte address, d5d6d700000
  digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer

}

void loop() {

     write_pot(pot,resistance);
     delay(10);
     resistance++;
     if (resistance==255)
     {
       pot++;
     }
     if (pot==6)
     {
       pot=0;
     }

}

First we set our input and output pin modes and set the SLAVESELECT line high to start. This deselects the device and avoids any false transmission messages due to line noise:

void setup()
{
  byte clr;
  pinMode(DATAOUT, OUTPUT);
  pinMode(DATAIN, INPUT);
  pinMode(SPICLOCK,OUTPUT);
  pinMode(SLAVESELECT,OUTPUT);
  digitalWrite(SLAVESELECT,HIGH); //disable device

Now we set the SPI Control register (SPCR) to the binary value 01010000. In the control register each bit sets a different functionality. The eighth bit disables the SPI interrupt, the seventh bit enables the SPI, the sixth bit chooses transmission with the most significant bit going first, the fifth bit puts the Arduino in Master mode, the fourth bit sets the data clock idle when it is low, the third bit sets the SPI to sample data on the rising edge of the data clock, and the second and first bits set the speed of the SPI to system speed / 4 (the fastest). After setting our control register up we read the SPI status register (SPSR) and data register (SPDR) in to the junk clr variable to clear out any spurious data from past runs:

  SPCR = (1<<SPE)|(1<<MSTR);
  clr=SPSR;
  clr=SPDR;
  delay(10);

We conclude the setup function by setting all the potentiometers to full on resistance states thereby turning the LEDs off:

  for (i=0;i<6;i++)
  {
    write_pot(i,255);
  }
}

The spi_transfer function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found here?. It then returns any data that has been shifted in to the data register by the EEPROM:

char spi_transfer(volatile char data)
{
  SPDR = data;                    // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  return SPDR;                    // return the received byte
}

The AD5206 is digitally controlled using SPI. The device is enabled by pulling the Chip Select (CS) pin low. Instructions are sent as 11 bit operational codes (opcodes) with the three most significant bits (11-9) defining the address of which potentiometer to adjust and the eight least significant bits (8-1) defining what value to set that potentiometer to from 0-255. Data is shifted in Most Significant Bit (MSB) first on the rising edge of the data clock. The data clock is idle when low, and the interface runs much faster than the Arduino, so we don't need to worry about pre-scaling to slow down the transmission.

Finally, connect an LED between each Wiper pin (AD5206 pins 2, 11, 14, 17, 20 and 23) and ground so that the long pin of the LED connects to the wiper and the short pin, or flat side of the LED connects to ground.

PICTURE leds

Program the Arduino

Now we will write the code to enable SPI control of the AD5206. This program will sequentially pulse each LED on and then fade it out gradually. This is accomplished in the main loop of the program by individually changing the resistance of each potentiometer from full off to full on over its full range of 255 steps.

We will walk through the code in small sections.

We define the pins we will be using for our SPI connection, DATAOUT, DATAIN, SPICLOCK and SLAVESELECT. Although we are not reading any data back out of the AD5206 in this program, pin 12 is attached to the builtin SPI so it is best not to use it for other programming functions to avoid any possible errors:

#define DATAOUT 11//MOSI
#define DATAIN 12//MISO - not used, but part of builtin SPI
#define SPICLOCK  13//sck
#define SLAVESELECT 10//ss

Next we allocate variables to store resistance values and address values for the potentiometers:

byte pot=0;
byte resistance=0;

The AD5206 is a 6 channel digital potentiometer. This means it has six variable resistors built in for individual electronic control. There are three pins on the chip for each of the six internal variable resistors, and they can be interfaced with just as you would use a mechanical potentiometer. The individual variable resistor pins are labeled Ax, Bx and Wx, ie. A1, B1 and W1.

The AD5206 is digitally controlled using SPI. The device is enabled by pulling the Chip Select (CS) pin low. Instructions are sent as 11 bit operational codes (opcodes) and are shifted in Most Significant Bit (MSB) first on the rising edge of the data clock. The data clock is idle when low, and the interface runs much faster than the Arduino, so we don't need to worry about pre-scaling to slow down the transmission.

Prepare the Breadboard

Insert the AD5206 chip into the breadboard. Connect 5V power and ground from the breadboard to 5V power and ground from the microcontroller. Connect AD5206 pins 3, 6, 10, 13, 16, 21 and 24 to 5v and pins 1, 4, 9, 12, 15, 18, 19, and 22 to ground. We are connecting all the A pins to ground and all of the B pins to 5v to create 6 voltage dividers.

PICTURE power

Connect AD5206 pin 5 to Arduino pin 10 (Slave Select - SS), AD5206 pin 7 to Arduino pin 11 (Master Out Slave In - MOSI), and AD5206 pin 8 to Arduino pin 13 (Serial Clock - SCK).

PICTURE datacom

The AD5206 is digitally controlled using standard SPI. The device is enabled by pulling the Chip Select (CS) pin low. Instructions are sent as 11 bit operational codes (opcodes) and are shifted in Most Significant Bit (MSB) first on the rising edge of the data clock. The data clock is idle when low, and the interface runs much faster than the Arduino, so we don't need to worry about pre-scaling to slow down the transmission.

The AD5206 is digitally controlled using standard SPI. The device is enabled by pulling the Chip Select (CS) pin low. Instructions are sent as 11 bit operational codes (opcodes) and are shifted in Most Significant Bit (MSB) first on the rising edge of the data clock. The data clock is idle when low, and the interface runs up to speeds of 100Mhz.

Controlling a Digital Potentiometer Using SPI

In this tutorial you will learn how to control the AD5206 digital potentiometer using Serial Peripheral Interface (SPI). For an explanation of SPI see the SPI EEPROM tutorial. Digital potentiometers are useful when you need to vary the resistance in a ciruit electronically rather than by hand. Example applications include LED dimming, audio signal conditioning and tone generation. In this example we will use a six channel digital potentiometer to control the brightness of six LEDs. The steps we will cover for implementing SPI communication can be modified for use with most other SPI devices.

Introduction to the AD5206 Digital Potentiometer

PICTURE pins

PICTURE pin functions

The AD5206 is a 6 channel digital potentiometer. This means it has six variable resistors built in for individual electronic control. There are three pins on the chip for each of the six internal variable resistors, and they can be interfaced with just as you would use a mechanical potentiometer.

For example, in this tutorial we will be using each variable resistor as a voltage divider by pulling one side pin (pin B) high, pulling another side pin (pin A) low and taking the variable voltage output of the center pin (Wiper).

The AD5206is controlled using standard SPI. The device is enabled by pulling the Chip Select (CS) pin low. Instructions are sent as 8 bit operational codes (opcodes) and are shifted in on the rising edge of the data clock.