Arduino code for Humidity sensors

// This code tests the SHT15 on the Arduino board.
// This app assumes your data pin is pin 10 and your your clock pin is pin 11.
// To run this app just attach HyperTerminal (or similar serial communications tool)
// to your Arduino board at 9600 bits per second. I also needed te set the
// flow control to none or I couldn't send commands to my Arduino board via HyperTerminal.
// Then press the 't' key to take a temperature reading or the 'h' key to take a
// humidity reading.

// These are commands we need to send to HSHT15 to control it
int gTempCmd = 0b00000011;
int gHumidCmd = 0b00000101;

int shiftIn(int dataPin, int clockPin, int numBits)
{
int ret = 0;
int i;

for (i=0; i {
digitalWrite(clockPin, HIGH);
delay(10); // I don't know why I need this, but without it I don't get my 8 lsb of temp
ret = ret*2 + digitalRead(dataPin);
digitalWrite(clockPin, LOW);
}

return(ret);
}

void sendCommandSHT(int command, int dataPin, int clockPin)
{
int ack;

// Transmission Start
pinMode(dataPin, OUTPUT);
pinMode(clockPin, OUTPUT);
digitalWrite(dataPin, HIGH);
digitalWrite(clockPin, HIGH);
digitalWrite(dataPin, LOW);
digitalWrite(clockPin, LOW);
digitalWrite(clockPin, HIGH);
digitalWrite(dataPin, HIGH);
digitalWrite(clockPin, LOW);

// The command (3 msb are address and must be 000, and last 5 bits are command)
shiftOut(dataPin, clockPin, MSBFIRST, command);

// Verify we get the coorect ack
digitalWrite(clockPin, HIGH);
pinMode(dataPin, INPUT);
ack = digitalRead(dataPin);
if (ack != LOW)
Serial.println("Ack Error 0");
digitalWrite(clockPin, LOW);
ack = digitalRead(dataPin);
if (ack != HIGH)
Serial.println("Ack Error 1");
}

void waitForResultSHT(int dataPin)
{
int i;
int ack;

pinMode(dataPin, INPUT);

for(i= 0; i < 100; ++i)
{
delay(10);
ack = digitalRead(dataPin);

if (ack == LOW)
break;
}

if (ack == HIGH)
Serial.println("Ack Error 2");
}

int getData16SHT(int dataPin, int clockPin)
{
int val;

// Get the most significant bits
pinMode(dataPin, INPUT);
pinMode(clockPin, OUTPUT);
val = shiftIn(dataPin, clockPin, 8);
val *= 256;

// Send the required ack
pinMode(dataPin, OUTPUT);
digitalWrite(dataPin, HIGH);
digitalWrite(dataPin, LOW);
digitalWrite(clockPin, HIGH);
digitalWrite(clockPin, LOW);

// Get the lest significant bits
pinMode(dataPin, INPUT);
val |= shiftIn(dataPin, clockPin, 8);

return val;
}

void skipCrcSHT(int dataPin, int clockPin)
{
// Skip acknowledge to end trans (no CRC)
pinMode(dataPin, OUTPUT);
pinMode(clockPin, OUTPUT);

digitalWrite(dataPin, HIGH);
digitalWrite(clockPin, HIGH);
digitalWrite(clockPin, LOW);
}

void setup()
{
Serial.begin(9600); // open serial
}

void loop()
{
int theDataPin = 10;
int theClockPin = 11;
char cmd = 0;
int ack;

while (Serial.available() > 0)
{
cmd = Serial.read();

switch (cmd)
{
case 't': //Read Temperature
{
int val;
int temp;

sendCommandSHT(gTempCmd, theDataPin, theClockPin);
waitForResultSHT(theDataPin);
val = getData16SHT(theDataPin, theClockPin);
skipCrcSHT(theDataPin, theClockPin);
Serial.print("Temp is:");
Serial.print(val, HEX);
temp = -40.0 + 0.018 * (float)val;
Serial.print(" ");
Serial.println(temp, DEC);
break;
}
case 'h': //Read Humidity
{
int val;
int humid;

sendCommandSHT(gHumidCmd, theDataPin, theClockPin);
waitForResultSHT(theDataPin);
val = getData16SHT(theDataPin, theClockPin);
skipCrcSHT(theDataPin, theClockPin);
Serial.print("Humidity is:");
Serial.print(val, HEX);
humid = -4.0 + 0.0405 * val + -0.0000028 * val * val;
Serial.print(" ");
Serial.println(humid, DEC);
break;
}
default:
{
Serial.println("You pressed something else");
}
}
}
}