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RHT03 Driver

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Joined: 10 Dec 2011
Posts: 376
Location: Sofiq,Bulgariq

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RHT03 Driver
PostPosted: Sat Mar 15, 2014 8:42 am     Reply with quote

In case you have to handle RHT03 (Temperature, Humidity) sensor, here is a driver which is tested. It works! The driver was developed thanks to these topics:
and the members involved in.

This is the code:

#INCLUDE <16F1508.h>
#USE delay(internal=16M, restart_wdt)
#USE rs232(BAUD=9600, UART1,ERRORS)

#define RHT_IO Pin_B6
#Define LED PIN_C7

#Include <RHT03.c>

void PrintData(int B1, int B2, int B3, int B4);

void main (void)
int8 i;
int8 ByteIndex[5];

output_high(led);    //Just for debugging WDT reset


While (True)
   SETUP_WDT(WDT_ON|WDT_32MS);                  //Prevent RHT03 Signal Stuck (will lead an infinite loop)
   RHT_Start();                                 //immediately after this line we must call reading of 40bits data
      for (i=0;i<5;i++)                         //5 bytes being read in this loop
         ByteIndex[i] = RHT_ReadData();
      printf("\r DATA Reception Succesful!");
      printf("\rDATA Garbage!");
   delay_ms(2300);                        //The process of data reception must last more than 2secs

void PrintData(int B1, int B2, int B3, int B4)
int16 humidity;
int16 temperature;
int1 TempSign;                         //the sign of the temperature (either minus or plus)
   TempSign = bit_test(B3,7);          //bit 7 determines if temerature is positive or negative, (=1 negative), (=0 positive)
   humidity = make16(B1,B2);           //assemble entire byte for humidity
   temperature = make16(B3,B4);        //assemble entire byte for temperature
   temperature &= 0b0111111111111111;  //exclude the sign of the temperature so I can convert it to a float value
   if(TempSign)                        //If temperature 15th bit is==1 the temperature value is negative
      printf(" T = -%.1f",(float)temperature/10);   //Note that I manualy put the minus sign
      printf(" T = %.1f",(float)temperature/10);
   printf(" RH = %.1f",(float)humidity/10);

And RHT03.C (driver):

void RHT03_Init(void)
   printf("\fRHT03 Initialization. . .");
   delay_ms(1500);                              //When power is supplied to sensor, don't send any instruction to the sensorwithin one second to pass unstable status
   printf("\fRHT03 Initialization done!");

void RHT_Start()
   output_low(RHT_IO);     // MCU pull low data bus  this process must beyond 1~10ms
   delay_ms(15);           // this process must beyond 1~10ms
   output_float(RHT_IO);   // MCU will pulls up and wait 20-40us for RHT03's response.
   while(input(RHT_IO));   // Wait for RHT03 pulls low the buss for 80uS as response signal
   while(!input(RHT_IO));   // Wait for RHT03 pulls up 80us for preparation to send data
   While(input(RHT_IO));   // RHT03 prepares data for being send (80uS)

int8 RHT_ReadData(void)    //RHT03 is sending data to MCU
int8 iIndex;
int8 iValue=0;
   for(iIndex = 0; iIndex < 8 ; iIndex++) //filling 8bit variable, bit by bit, according to RHT03 input state,
      while(!input(RHT_IO));     // every bit's transmission begin with low-voltage-level that last 50us
      shift_left(&iValue, 1, input(RHT_IO));
   return iValue;

You may change the timings if you consider as right.
Very important thing is not to forget the pull-up resistor 1K on RHT_IO pin!
A person who never made a mistake never tried anything new.
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