File content as of revision 0:09dd83d78a0a:

#include "mbed.h"
#include "VCNL40x0.h"
#include "NeoStrip.h"
#define #define NumPixels 4

I2C i2c(p28, p27);
DigitalOut mled0(LED1); 
DigitalOut mled1(LED2); 
DigitalOut mled2(LED3); 
DigitalOut mled3(LED4); 
Serial pc(USBTX, USBRX);
DigitalOut reset(p29);
NeoStrip strip(p26, NumPixels);

const uint8_t MUX = 0xE0; // 11100000
const uint8_t VCNL4020 = 0x26;
unsigned int sensors[4];
char _send[3];
char _receive[2];
char port[2];
const uint8_t chan[] = {0x01,0x02,0x04,0x08};
int mleds[] = {0,0,0,0};

void Setup(void);
void Setmleds(void);
void SwitchChannel(uint8_t chan);
void ReadAllSensors(void);
void Setmleds(void);
void SetProximityRate (unsigned char ProximityRate);
void SetCommandRegister (unsigned char Command);
void ReadCommandRegister (unsigned char *Command);
void SetCurrent (unsigned char Current);
void ReadProxiValue (unsigned int *ProxiValue);
void SetProximityRate (unsigned char ProximityRate);
void ReadProxiOnDemand (unsigned int *ProxiValue);
void Setup(void);


////////////////////////////////////////////////////////////////////////////////////////////////////////////////

int main() {
    
    Setup();
    
    while (1) {
        
        ReadAllSensors();
        
    }
}


////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void Setup(void) {
    
    pc.baud(115200);    
                                    // set BAUD
    for (int i = 0; i < 4; i++){
            
            reset = 0;
            wait(0.001);
            reset = 1;
            wait(0.001);
            port[0] = chan[i];
            i2c.write(MUX,port, 1);
            SetCurrent(20);                              // Set current to 200mA
            SetCommandRegister (COMMAND_ALL_DISABLE);    // ready for prox rate change
            SetProximityRate (PROX_MEASUREMENT_RATE_31); // 31 measurements/s
            wait(0.2);
            
        }
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void Setmleds(void){
    mled0 = mleds[0];
    mled1 = mleds[1];
    mled2 = mleds[2];
    mled3 = mleds[3];
    }

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void SwitchChannel(uint8_t chan){
        reset = 0;
        wait(0.001);
        reset = 1;
        wait(0.001);    
        port[0] = chan;
        i2c.write(MUX,port, 1);
    }

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void ReadAllSensors(void){
    
    for (int i = 0; i < 4; i++){
            
        SwitchChannel(chan[i]);            // set channel
        mleds[i] = 1;                      // LED on
        Setmleds();
        ReadProxiOnDemand(&sensors[i]);    // read prox value on demand
        mleds[i] = 0;                      // LED off
        Setmleds();    
        }
        
        for (int i = 0; i < 4; i++){
        pc.printf("\r %i ", sensors[i]);
        }
    pc.printf("\r \n ");};
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void SetCommandRegister (unsigned char Command) {
    
    //unsigned char send[2];
    
    _send[0] = REGISTER_COMMAND;                   // VCNL40x0 Configuration reister
    _send[1] = Command;
    i2c.write(VCNL4020,_send, 2);                  // Write 2 bytes on I2C
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void ReadCommandRegister (unsigned char *Command) {
    
    //unsigned char send[2];
    //unsigned char receive[2];

    _send[0] = REGISTER_COMMAND;                   // VCNL40x0 Configuration register
    i2c.write(VCNL4020,_send, 1);                  // Write 1 byte on I2C
    i2c.read(VCNL4020+1,_receive, 1);              // Read 1 byte on I2C

    *Command = (unsigned char)(_receive[0]);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void SetCurrent (unsigned char Current) {

    _send[0] = REGISTER_PROX_CURRENT;              // VCNL40x0 IR LED Current register
    _send[1] = Current;
    i2c.write(VCNL4020,_send, 2);                  // Write 2 bytes on I2C

}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void ReadProxiValue (unsigned int *ProxiValue) {

    _send[0] = REGISTER_PROX_VALUE;                // VCNL40x0 Proximity Value register
    i2c.write(VCNL4020, _send, 1);                 // Write 1 byte on I2C
    i2c.read(VCNL4020+1, _receive, 2);             // Read 2 bytes on I2C
    *ProxiValue = ((unsigned int)_receive[0] << 8 | (unsigned char)_receive[1]);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void SetProximityRate (unsigned char ProximityRate) {

    _send[0] = REGISTER_PROX_RATE;                 // VCNL40x0 Proximity rate register
    _send[1] = ProximityRate;
    i2c.write(VCNL4020,_send, 2);                  // Write 2 bytes on I2C
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////

void ReadProxiOnDemand (unsigned int *ProxiValue) {

    unsigned char Command=0;

    // enable prox value on demand
    SetCommandRegister (COMMAND_PROX_ENABLE | COMMAND_PROX_ON_DEMAND);
 
    // wait on prox data ready bit
    do {
        ReadCommandRegister (&Command);                     // read command register
    } while (!(Command & COMMAND_MASK_PROX_DATA_READY));

    ReadProxiValue (ProxiValue);                            // read prox value

    SetCommandRegister (COMMAND_ALL_DISABLE);               // stop prox value on demand
    
}