#include <SPI.h>

const int outputPwm = 9;
const int inputPwn = 1;
const int slaveSelectPin = 10;

void Setup(){
    pinMode(outputPwm, OUTPUT);
    pinMode(inputPwn, INPUT);
    pinMode(slaveSelectPin, OUTPUT);
    SPI.begin();
}

void loop(){
    int channel = 0b00010001;
    pwm_led();
    for (int level = 0; level < 255; ++level)
    {
        digitalPotWrite(channel, level);
        delay(5);
    }
}

void digitalPotWrite(int address, int value){
    digitalWrite(slaveSelectPin, LOW);
    SPI.transfer(address);
    SPI.transfer(value);
    digitalWrite(slaveSelectPin, HIGH);
}

void pwm_led(){
    int level = analogRead(inputPwn);
    analogWrite(outputPwm, level);
}