MCP425X

Arduino library for controlling the Microchip MCP4251/MCP4252 digital potentiometers.

Compatibility

Currently compatible with MCP4251, MCP4252,MCP4231, MCP4232 digital potentiometers, but support is planned for further models.
Tested with the following Arduino boards, but it should be compatible with any boards that can support SPI:

• Arduino Uno
• Adafruit Metro M0 Expressto

Installation

To install open Arduino IDE -> Sketch -> Include Library -> Add .ZIP Library... and select the source code (.zip) file.

Usage

To use, simply include MCP425X.h in your sketch.

Initialization

Each potentiometer connected to the Arduino is an instance of the Microchip_MCP4251 class.

MCP425X/src/MCP425X.h

Lines 26 to 27 in 4e0578f

	Microchip_MCP4251(uint8_t CSPin, uint16_t resistance);
	Microchip_MCP4251(uint8_t CSPin, uint16_t resistance, SPISettings SPIConf);

The constructor of the class requires the resistance of the potentiometer, as well as the pin for the chip select line, to be passed as arguments. Optionally, the default SPI settings (10MHz and Mode 0 as recommended by Microchip) can be overridden. In the setup() section of the sketch, begin() needs to be called to initialize the CS pins and the SPI bus. This needs to be called before any other operations are run on the potentiometer. Below is an example initialization:

Microchip_MCP4251 digiPot(5, 10000);

void setup()
{
    digiPot.begin();
}

Operations

This library supports all the operations that are possible with the digital potentiometers, with the exception of shutdown. This can still be achieved by manually toggling the shutdown pin of the potentiometer using digitalWrite(). All commands will set commandError to true if they fail. Any subsequent successful commands will set it back to false. To select which potentiometer an operation is for, either P0 or P1 needs to be passed in the potSelect argument.

Incrementing/Decrementing the wiper

To increment/decrement the wiper, the following functions are provided.

MCP425X/src/MCP425X.h

Lines 31 to 35 in 4e0578f

	void incrementWiper(potSelect_t potSelect);
	void incrementWiper(potSelect_t potSelect, uint16_t n);
	void decrementWiper(potSelect_t potSelect);
	void decrementWiper(potSelect_t potSelect, uint16_t n);

It is the responsibility of the user to know if the wiper has reached the max/min position, as further increment/decrement commands will have no effect on the wipers position.

Setting/Getting the wiper

The wiper position is stored in volatile memory in the IC. Therefore, it can be set or retrieved directly using the setWiper() and getWiper() functions.

MCP425X/src/MCP425X.h

Lines 37 to 38 in 4e0578f

	uint16_t getWiper(potSelect_t potSelect);
	void setWiper(potSelect_t potSelect, uint16_t position);

One must take care to not exceed 9-bit values (or 0x100) when setting the wiper, as it's the maximum value the 8-bit digital potentiometers use, respectively 0x80 is the max for 7-bit models.

Setting/Getting the resistance

Instead of setting the wiper position directly as an unsigned integer between 0x00 and 0x100, the resistance between terminal B and the wiper can be set and retrieved using the setResistance() andgetResistance() functions.

MCP425X/src/MCP425X.h

Lines 40 to 41 in 4e0578f

	uint16_t getResistance(potSelect_t potSelect);
	void setResistance(potSelect_t potSelect, uint16_t resistance);

Getting the status

The getStatus function can be used to get the status of the potentiometer (if in shutdown or normal state).

MCP425X/src/MCP425X.h

Line 43 in 4e0578f

bool getStatus();

Deinitialization

After use of the potentiometers have finished, SPI.end() can be safely called to disable the SPI bus. An additional call to begin() can re-establish normal functionality.