/*************************************************************
Dual Digital Pot (100K)
<https://www.dfrobot.com/wiki/index.php/Dual_Digital_Pot_(100K)_SKU:_DFR
0520>
*************************************************************
This example serves as a template to control the MCP42100 dual
digital pot through 3-wire SPI.
Created 2017-8-31
By Henry Zhao <Henry.zhao@dfrobot.com>
GNU Lesser Genral Public License.
See <http://ww.gnu.org/licenses/> for details.
All above must be included in any redistribution.
************************************************************/
/********************Device Inctrduction**********************
The MCP42100 has dual potentiometer x (x=0,1).
Ax - Potenriometer terminal Ax
Wx - Potenriometer Wiper
Bx - Potenriometer terminal Bx
SI - Serial Data Input
SCK - Serial Clock
CS - Chip Select
The MCP42100 is SPI-compatible,and two bytes should be sent to control i
t.
The first byte specifies the potentiometer (POT0: 0x11, POT1: 0x12, both
: 0x13).
The second byte specifies resistance value for the pot (0 - 255).
************************************************************/
/***********************Circuit Connections*******************
Digital Pot | Arduino UNO R3
CS | D10 (SS)
SI | D11 (MOSI)
CLK | D13 (SCK)
VCC | VCC
GND | GND
************************************************************/
/***********************Resistances Calculation**************
Rwa(Dn) =Rab*(256 - Dn) / 256 + Rw
Rwb(Dn) =Rab*Dn / 256 + Rw
Rwa - resistance between Terminal A and wiper W
Rwb - resistance between Terminal B and wiper W
Rab - overall resistance for the pot （=100KΩ, typical）
Rw - wiper resistance （=125Ω,typical; =175Ω max）
Dn - 8-bit value in data register for pot number n （= 0 - 255）
************************************************************/
/***********************Notice********************************
1.Resistor terminals A, B and W have no restrictions on
polarity with respect to each other.
2.Current through terminals A, B and W should not excceed ±1mA.
3.Voltages on terminals A, B and W should be within 0 - VCC.
************************************************************/
#include <SPI.h>
/***********************PIN Definitions*************************/
// set pin 10 as the slave select for the digital pot:
const int CS_PIN = 10;
/***********************MCP42XXX Commands************************/
//potentiometer select byte
const int POT0_SEL = 0x11;
const int POT1_SEL = 0x12;
const int BOTH_POT_SEL = 0x13;
//shutdown the device to put it into power-saving mode.
//In this mode, terminal A is open-circuited and the B and W terminals are sh
orted together.
//send new command and value to exit shutdowm mode.
const int POT0_SHUTDOWN = 0x21;
const int POT1_SHUTDOWN = 0x22;
const int BOTH_POT_SHUTDOWN = 0x23;
/***********************Customized Varialbes**********************/
//resistance value byte (0 - 255)
//The wiper is reset to the mid-scale position upon power-up, i.e. POT0_Dn =
POT1_Dn = 128
int POT0_Dn = 128;
int POT1_Dn = 128;
int BOTH_POT_Dn = 128;
//Function Declaration
void DigitalPotTransfer(int cmd, int value); //send the command and the r
esistance value through SPI
void setup()
{
pinMode(CS_PIN, OUTPUT); // set the CS_PIN as an output:
SPI.begin(); // initialize SPI:
DigitalPotWrite(BOTH_POT_SHUTDOWN, BOTH_POT_Dn);
}
void loop()
{
DigitalPotWrite(POT0_SEL, POT0_Dn); //set the resistance of
POT0
DigitalPotWrite(POT1_SEL, POT1_Dn); //set the resistance of
POT1
//DigitalPotWrite(BOTH_POT_SEL, BOTH_POT_Dn); //set the resistance
of both potentiometers
//DigitalPotWrite(POT0_SHUTDOWN, POT0_Dn); //put POT0 into shu
ntdowm mode, ignore the second parameter
//DigitalPotWrite(POT1_SHUTDOWN, POT1_Dn); //put POT1 into shu
ntdowm mode, ignore the second parameter
//DigitalPotWrite(BOTH_POT_SHUTDOWN, BOTH_POT_Dn); //put both potentio
meters into shuntdowm mode, ignore the second parameter
}
void DigitalPotWrite(int cmd, int val)
{
// constrain input value within 0 - 255
val = constrain(val, 0, 255);
// set the CS pin to low to select the chip:
digitalWrite(CS_PIN, LOW);
// send the command and value via SPI:
SPI.transfer(cmd);
SPI.transfer(val);
// Set the CS pin high to execute the command:
digitalWrite(CS_PIN, HIGH);
}
