Frequency to voltage

I am using TCS 3200 color sensor and the output is obtained in the from of frequency
how to convert frequency output in voltage form. i want to display color sensor output in the form of voltage. I am using this code.

#define S0 4
#define S1 5
#define S2 6
#define S3 7
#define sensorOut 8
int frequency = 0;
void setup() {
pinMode(S0, OUTPUT);
pinMode(S1, OUTPUT);
pinMode(S2, OUTPUT);
pinMode(S3, OUTPUT);
pinMode(sensorOut, INPUT);

// Setting frequency-scaling to 20%
digitalWrite(S0,HIGH);
digitalWrite(S1,LOW);

Serial.begin(9600);
}
void loop() {
// Setting red filtered photodiodes to be read
digitalWrite(S2,LOW);
digitalWrite(S3,LOW);
// Reading the output frequency
frequency = pulseIn(sensorOut, LOW);
// Printing the value on the serial monitor
Serial.print("R= ");//printing name
Serial.print(frequency);//printing RED color frequency
Serial.print(" ");
delay(100);
// Setting Green filtered photodiodes to be read
digitalWrite(S2,HIGH);
digitalWrite(S3,HIGH);
// Reading the output frequency
frequency = pulseIn(sensorOut, LOW);
// Printing the value on the serial monitor
Serial.print("G= ");//printing name
Serial.print(frequency);//printing RED color frequency
Serial.print(" ");
delay(100);
// Setting Blue filtered photodiodes to be read
digitalWrite(S2,LOW);
digitalWrite(S3,HIGH);
// Reading the output frequency
frequency = pulseIn(sensorOut, LOW);
// Printing the value on the serial monitor
Serial.print("B= ");//printing name
Serial.print(frequency);//printing RED color frequency
Serial.println(" ");
delay(100);
}

Why voltage?
The relative values of the red/green/blue channels will tell you the colour.

In my project I need voltage value for further processing according to my requirement.

ShipraSingh:
In my project I need voltage value for further processing according to my requirement.

Your sensor has a frequency output which your code measures and displays.

There is no analogue voltage to measure therefore the requirement doesn't make sense.

However, if you want a number that vaguely looks like something an analogue sensor would generate then simply divide all the frequency values by some number so that the values fall somewhere between 0 and 5.

Following on from mikb55.

The MAP function would probably be of use to you.

Bob.

ballscrewbob is on the correct track. You can convert the counts to "voltage" actually a number that represents a voltage, the inverse of what you do with a A/D. This allows you to adjust the range to whatever you want and to tweak it as well. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil