libsht.c

Driver for SHT1x temperature and humidity sensor. Code for AVR Microcontroller.

/***********************************************************************************
Sensirion SHTxx Sensor Library 0v2

***********************************************************************************/
/* Copyright Notice
 	This library for the SHT temperature and humidity sensors is based on the 
	application datasheet "Sample Code humidity sensor SHTxx" from Sensirion. 
	(c) Timo Dittmar
		(For now. If I get enough feedback and a positive answer from
		Sensirion I plan to release the code under GPL)
	Use without any warranty
*/


/* History
	Date, Version, Comment 
	2006-07-14	NA		- Initial conversion from Sensirion application note
						- inserted test code
	2006-07-17	NA		- Adjusted timing in measurement
						- changed data transfer in calc_sht; 
	2006-07-20	0v1rc	- Included heating element code 
	2006-08-05	0v1		- Some additional cleanup
						- homogenized function names;
	2006-08-13	0v2rc	- included functions for measuring with recurring interrupt
						- fewer orthographic errors :-)
						- first implementation of crc check
	2006-08-27	0v2		- second release
*/

#include <avr/io.h> //Microcontroller specific library, e.g. port definitions
#include <math.h> //
#include <stdlib.h> //
#include <inttypes.h> // 
#include <util/delay.h>
#include "libsht.h"
#include <avr/pgmspace.h>

const uint8_t CRC_TABLE[] PROGMEM = {0, 49, 98, 83, 196, 245, 166, 151,
 185, 136, 219, 234, 125, 76, 31, 46, 67, 114, 33, 16, 135, 182, 229,
 212, 250, 203, 152, 169, 62, 15, 92, 109, 134, 183, 228, 213, 66, 115,
 32, 17, 63, 14, 93, 108, 251, 202, 153, 168, 197, 244, 167, 150, 1,
 48, 99, 82, 124, 77, 30, 47, 184, 137, 218, 235, 61, 12, 95, 110, 249,
 200, 155, 170, 132, 181, 230, 215, 64, 113, 34, 19, 126, 79, 28, 45,
 186, 139, 216, 233, 199, 246, 165, 148, 3, 50, 97, 80, 187, 138, 217,
 232, 127, 78, 29, 44, 2, 51, 96, 81, 198, 247, 164, 149, 248, 201, 
 154, 171, 60, 13, 94, 111, 65, 112, 35, 18, 133, 180, 231, 214, 122, 
 75, 24, 41, 190, 143, 220, 237, 195, 242, 161, 144, 7, 54, 101, 84, 
 57, 8, 91, 106, 253, 204, 159, 174, 128, 177, 226, 211, 68, 117, 38, 
 23, 252, 205, 158, 175, 56, 9, 90, 107, 69, 116, 39, 22, 129, 176, 227, 
 210, 191, 142, 221, 236, 123, 74, 25, 40, 6, 55, 100, 85, 194, 243, 
 160, 145, 71, 118, 37, 20, 131, 178, 225, 208, 254, 207, 156, 173, 58, 
 11, 88, 105, 4, 53, 102, 87, 192, 241, 162, 147, 189, 140, 223, 238, 
 121, 72, 27, 42, 193, 240, 163, 146, 5, 52, 103, 86, 120, 73, 26, 43, 
 188, 141, 222, 239, 130, 179, 224, 209, 70, 119, 36, 21, 59, 10, 89, 
 104, 255, 206, 157, 172};
 
 const uint8_t REVERSED_BIT_ORDER_LIST[] PROGMEM = { 0, 128, 64, 192, 32, 160, 96, 224, 16, 144, 80, 208, 48, 176, 112, 
 240, 8, 136, 72, 200, 40, 168, 104, 232, 24, 152, 88, 216, 56, 184, 
 120, 248, 4, 132, 68, 196, 36, 164, 100, 228, 20, 148, 84, 212, 52, 
 180, 116, 244, 12, 140, 76, 204, 44, 172, 108, 236, 28, 156, 92, 220, 
 60, 188, 124, 252, 2, 130, 66, 194, 34, 162, 98, 226, 18, 146, 82, 
 210, 50, 178, 114, 242, 10, 138, 74, 202, 42, 170, 106, 234, 26, 
 154, 90, 218, 58, 186, 122, 250, 6, 134, 70, 198, 38, 166, 102, 230, 
 22, 150, 86, 214, 54, 182, 118, 246, 14, 142, 78, 206, 46, 174, 110, 
 238, 30, 158, 94, 222, 62, 190, 126, 254, 1, 129, 65, 193, 33, 161, 
 97, 225, 17, 145, 81, 209, 49, 177, 113, 241, 9, 137, 73, 201, 41, 
 169, 105, 233, 25, 153, 89, 217, 57, 185, 121, 249, 5, 133, 69, 197, 
 37, 165, 101, 229, 21, 149, 85, 213, 53, 181, 117, 245, 13, 141, 77, 
 205, 45, 173, 109, 237, 29, 157, 93, 221, 61, 189, 125, 253, 3, 131, 
 67, 195, 35, 163, 99, 227, 19, 147, 83, 211, 51, 179, 115, 243, 11, 
 139, 75, 203, 43, 171, 107, 235, 27, 155, 91, 219, 59, 187, 123, 251, 
 7, 135, 71, 199, 39, 167, 103, 231, 23, 151, 87, 215, 55, 183, 119, 
 247, 15, 143, 79, 207, 47, 175, 111, 239, 31, 159, 95, 223, 63, 191, 127, 255};



//----------------------------------------------------------------------------------
unsigned char sht_write_byte(unsigned char sht_value)
//----------------------------------------------------------------------------------
// writes a byte on the Sensibus and checks the acknowledge
{
unsigned char i;
unsigned char error=0;
MAKE_SHT_DATA_PIN_OUTPUT;
asm volatile ("nop"::); // necessary because of the sync circuitry 
for (i=0x80;i>0;i/=2) //shift bit for masking
	{if (i & sht_value) SET_SHT_DATA; //masking value with i , write to SENSI-BUS
	 else CLEAR_SHT_DATA;
	 SET_SHT_SCK; //clk for SENSI-BUS
	 asm volatile ("nop"::);
	 asm volatile ("nop"::);
	 CLEAR_SHT_SCK;
	 asm volatile ("nop"::);
	 asm volatile ("nop"::);
	}
SET_SHT_DATA; //release DATA-line
MAKE_SHT_DATA_PIN_INPUT;
asm volatile ("nop"::);
SET_SHT_SCK; //clk #9 for ack
asm volatile ("nop"::);
asm volatile ("nop"::);
if (SHT_DATA) error =1; //check ack (DATA will be pulled down by SHT11)
CLEAR_SHT_SCK;
return error; //error=1 in case of no acknowledge
}



//----------------------------------------------------------------------------------
unsigned char sht_read_byte(unsigned char ack)
//----------------------------------------------------------------------------------
// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
{
unsigned char i;
unsigned char val=0;
MAKE_SHT_DATA_PIN_OUTPUT;
asm volatile ("nop"::); // necessary because of the sync circuitry
SET_SHT_DATA; //release DATA-line
MAKE_SHT_DATA_PIN_INPUT;
asm volatile ("nop"::); // necessary because of the sync circuitry
for (i=0x80;i>0;i/=2) //shift bit for masking
	{ SET_SHT_SCK; //clk for SENSI-BUS
	 asm volatile ("nop"::); 
	 asm volatile ("nop"::);
	 if (SHT_DATA) val=(val | i); //read bit
	 CLEAR_SHT_SCK;
	 asm volatile ("nop"::); 
	 asm volatile ("nop"::);
	}
MAKE_SHT_DATA_PIN_OUTPUT;
asm volatile ("nop"::); // necessary because of the sync circuitry
if (ack) CLEAR_SHT_DATA; else SET_SHT_DATA; // Sent ack
SET_SHT_SCK; //clk #9 for ack
asm volatile ("nop"::);
asm volatile ("nop"::);
asm volatile ("nop"::);
CLEAR_SHT_SCK;
asm volatile ("nop"::);
asm volatile ("nop"::);
SET_SHT_DATA; //release DATA-line
return val;
}



//----------------------------------------------------------------------------------
void sht_transstart(void)
//----------------------------------------------------------------------------------
// generates a transmission start
{
MAKE_SHT_DATA_PIN_OUTPUT;
asm volatile ("nop"::);
SET_SHT_DATA; CLEAR_SHT_SCK; //Initial state
asm volatile ("nop"::);
asm volatile ("nop"::);
SET_SHT_SCK;
asm volatile ("nop"::);
asm volatile ("nop"::);
CLEAR_SHT_DATA;
asm volatile ("nop"::);
asm volatile ("nop"::);
CLEAR_SHT_SCK;
asm volatile ("nop"::);
asm volatile ("nop"::);
asm volatile ("nop"::);
asm volatile ("nop"::);
asm volatile ("nop"::);
asm volatile ("nop"::);
SET_SHT_SCK;
asm volatile ("nop"::);
asm volatile ("nop"::);
SET_SHT_DATA;
asm volatile ("nop"::);
asm volatile ("nop"::);
CLEAR_SHT_SCK;
}


//----------------------------------------------------------------------------------
void sht_connectionreset(void)
//----------------------------------------------------------------------------------
// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
{
unsigned char i;
MAKE_SHT_DATA_PIN_OUTPUT;
asm volatile ("nop"::);
SET_SHT_DATA; CLEAR_SHT_SCK; //Initial state
for(i=0;i<9;i++) //9 SCK cycles
{ SET_SHT_SCK;
asm volatile ("nop"::);
asm volatile ("nop"::);
CLEAR_SHT_SCK;
asm volatile ("nop"::);
asm volatile ("nop"::);
}
sht_transstart(); //transmission start
}



//----------------------------------------------------------------------------------
unsigned char sht_softreset(void)
//----------------------------------------------------------------------------------
// resets the sensor by a softreset
{
unsigned char error=0;
sht_connectionreset(); //reset communication
error+=sht_write_byte(RESET); //send RESET-command to sensor
return error; //error=1 in case of no response form the sensor
}