}

}

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);

}

Experiment Results

Two triangular waves out of phase can be observed from the oscilloscope. If we zoom in a section of

the wave, the triangular wave is actually made up of many steps. Each steps correspond to one

wiper position. The width of the step is about 1ms, because the program delay for 1ms between

every wiper changes. The upstairs half cycle and the downstairs half cycle consist of 256 steps

each, therefore the period of the triangular wave is 256*2=512ms. The digital pot can quickly change

the wiper position and the settling time can up to micro seconds (18μs, typical).

Experiment Results