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SHT_v1/SHT.cpp@0:126d52039477, 2010-12-01 (annotated)

Committer:: okini3939
Date:: Wed Dec 01 15:13:50 2010 +0000
Revision:: 0:126d52039477

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User	Revision	Line number	New contents of line
okini3939	0:126d52039477	1	/* mbed module to use a Sensirion SHT1x /SHT7x sensor
okini3939	0:126d52039477	2	* Copyright (c) 2007-2009 Stephen McGarry
okini3939	0:126d52039477	3	* Released under the MIT License: http://mbed.org/license/mit
okini3939	0:126d52039477	4	*/
okini3939	0:126d52039477	5
okini3939	0:126d52039477	6	#include "SHT.h"
okini3939	0:126d52039477	7
okini3939	0:126d52039477	8	#include "mbed.h"
okini3939	0:126d52039477	9
okini3939	0:126d52039477	10	SHT::SHT(PinName p_sclk, PinName p_data, SHT_acc p_accuracy) : sclk(p_sclk), data(p_data), accuracy(p_accuracy) {
okini3939	0:126d52039477	11	sclk=0;
okini3939	0:126d52039477	12	data=0; // data pin will be used as open collector pin
okini3939	0:126d52039477	13	data.mode(PullUp); // with the pull up internally active
okini3939	0:126d52039477	14	data.input(); // with line released to go high
okini3939	0:126d52039477	15	temperature = humidity = dewpoint=0.0f;
okini3939	0:126d52039477	16	printf("constructor\n");
okini3939	0:126d52039477	17	}
okini3939	0:126d52039477	18
okini3939	0:126d52039477	19	char SHT::write_byte(byte value)
okini3939	0:126d52039477	20	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	21	// writes a byte on the Sensibus and checks the acknowledge
okini3939	0:126d52039477	22	{
okini3939	0:126d52039477	23	int i;
okini3939	0:126d52039477	24	char error=0;
okini3939	0:126d52039477	25
okini3939	0:126d52039477	26	for (i=0x80;i>0;i/=2) { //shift bit for masking
okini3939	0:126d52039477	27	if (i & value) data.input(); //masking value with i , write to SENSI-BUS
okini3939	0:126d52039477	28	else data.output();
okini3939	0:126d52039477	29	wait_us(1); //ensure sclk is low for min time
okini3939	0:126d52039477	30	sclk=1; //clk for SENSI-BUS
okini3939	0:126d52039477	31	wait_us(1); //pulsewith approx. 2 us
okini3939	0:126d52039477	32	sclk=0;
okini3939	0:126d52039477	33	}
okini3939	0:126d52039477	34	data.input(); //release DATA-line
okini3939	0:126d52039477	35	wait_us(1); //ensure sclk is low for min time
okini3939	0:126d52039477	36	sclk=1; //clk #9 for ack
okini3939	0:126d52039477	37	error=data; //check ack (DATA will be pulled down by SHT11)
okini3939	0:126d52039477	38	wait_us(1);
okini3939	0:126d52039477	39	sclk=0;
okini3939	0:126d52039477	40	return error; //error=1 in case of no acknowledge
okini3939	0:126d52039477	41	}
okini3939	0:126d52039477	42
okini3939	0:126d52039477	43	byte SHT::read_byte(bool send_ack)
okini3939	0:126d52039477	44	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	45	// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
okini3939	0:126d52039477	46	{
okini3939	0:126d52039477	47	byte i,val=0;
okini3939	0:126d52039477	48	data.input(); //release DATA-line
okini3939	0:126d52039477	49	for (i=0x80;i>0;i/=2) { //shift bit for masking
okini3939	0:126d52039477	50	wait_us(1);
okini3939	0:126d52039477	51	sclk=1; //clk for SENSI-BUS
okini3939	0:126d52039477	52	if (data) val=(val \| i); //read bit
okini3939	0:126d52039477	53	wait_us(1);
okini3939	0:126d52039477	54	sclk=0;
okini3939	0:126d52039477	55	}
okini3939	0:126d52039477	56	wait_us(1);
okini3939	0:126d52039477	57	if (send_ack) data.output(); // if ack needed then drive data low
okini3939	0:126d52039477	58	sclk=1; //clk #9 for ack
okini3939	0:126d52039477	59	wait_us(1);
okini3939	0:126d52039477	60	sclk=0;
okini3939	0:126d52039477	61	data.input(); //release DATA-line
okini3939	0:126d52039477	62	return val;
okini3939	0:126d52039477	63	}
okini3939	0:126d52039477	64
okini3939	0:126d52039477	65	void SHT::trans_start(void)
okini3939	0:126d52039477	66	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	67	// generates a transmission start
okini3939	0:126d52039477	68	// _____ ________
okini3939	0:126d52039477	69	// DATA: \|_______\|
okini3939	0:126d52039477	70	// ___ ___
okini3939	0:126d52039477	71	// SCK : ___\| \|___\| \|______
okini3939	0:126d52039477	72	{
okini3939	0:126d52039477	73	data.input();
okini3939	0:126d52039477	74	sclk=0; //Initial state
okini3939	0:126d52039477	75	wait_us(1);
okini3939	0:126d52039477	76	sclk=1;
okini3939	0:126d52039477	77	wait_us(1);
okini3939	0:126d52039477	78	data.output(); // data low
okini3939	0:126d52039477	79	wait_us(1);
okini3939	0:126d52039477	80	sclk=0;
okini3939	0:126d52039477	81	wait_us(1);
okini3939	0:126d52039477	82	sclk=1;
okini3939	0:126d52039477	83	wait_us(1);
okini3939	0:126d52039477	84	data.input(); // allow data to high
okini3939	0:126d52039477	85	wait_us(1);
okini3939	0:126d52039477	86	sclk=0;
okini3939	0:126d52039477	87	wait_us(1);
okini3939	0:126d52039477	88	}
okini3939	0:126d52039477	89
okini3939	0:126d52039477	90	void SHT::connection_reset(void)
okini3939	0:126d52039477	91	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	92	// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
okini3939	0:126d52039477	93	// _____________________________________________________ ________
okini3939	0:126d52039477	94	// DATA: \|_______\|
okini3939	0:126d52039477	95	// _ _ _ _ _ _ _ _ _ ___ ___
okini3939	0:126d52039477	96	// SCK : __\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|______\| \|___\| \|______
okini3939	0:126d52039477	97	{
okini3939	0:126d52039477	98	int i;
okini3939	0:126d52039477	99	data.input(); // allow data high
okini3939	0:126d52039477	100	sclk=0; // and clk low
okini3939	0:126d52039477	101	for (i=0;i<9;i++) { // 9 SCK cycles
okini3939	0:126d52039477	102	wait_us(1);
okini3939	0:126d52039477	103	sclk=1;
okini3939	0:126d52039477	104	wait_us(1);
okini3939	0:126d52039477	105	sclk=0;
okini3939	0:126d52039477	106	}
okini3939	0:126d52039477	107	}
okini3939	0:126d52039477	108	char SHT::soft_reset(void)
okini3939	0:126d52039477	109	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	110	// resets the sensor by a softreset
okini3939	0:126d52039477	111	{
okini3939	0:126d52039477	112	char error=0;
okini3939	0:126d52039477	113	SHT::connection_reset(); //reset communication
okini3939	0:126d52039477	114	trans_start();
okini3939	0:126d52039477	115	error+=write_byte(com_reset); //send RESET-command to sensor
okini3939	0:126d52039477	116	return error; //error=1 in case of no response form the sensor
okini3939	0:126d52039477	117	}
okini3939	0:126d52039477	118
okini3939	0:126d52039477	119	char SHT::read_status(byte &value)
okini3939	0:126d52039477	120	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	121	// reads the status register with checksum (8-bit)
okini3939	0:126d52039477	122	{
okini3939	0:126d52039477	123	//byte checksum;
okini3939	0:126d52039477	124
okini3939	0:126d52039477	125	char error=0;
okini3939	0:126d52039477	126	trans_start(); //transmission start
okini3939	0:126d52039477	127	error=write_byte(com_read_status_reg); //send command to sensor
okini3939	0:126d52039477	128	value=read_byte(send_ack); //read status register (8-bit)
okini3939	0:126d52039477	129	/* checksum= */
okini3939	0:126d52039477	130	(void)read_byte(no_ack); //read checksum (8-bit)
okini3939	0:126d52039477	131	// check the checksum ??
okini3939	0:126d52039477	132	return error; //error=1 in case of no response form the sensor
okini3939	0:126d52039477	133	}
okini3939	0:126d52039477	134
okini3939	0:126d52039477	135	char SHT::write_status(byte value)
okini3939	0:126d52039477	136	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	137	// writes the status register (8-bit)
okini3939	0:126d52039477	138	{
okini3939	0:126d52039477	139	char error=0;
okini3939	0:126d52039477	140	trans_start(); //transmission start
okini3939	0:126d52039477	141	error+=write_byte(com_write_status_reg); //send command to sensor
okini3939	0:126d52039477	142	error+=write_byte(value); //send value of status register
okini3939	0:126d52039477	143	return error; //error>=1 in case of no response form the sensor
okini3939	0:126d52039477	144	}
okini3939	0:126d52039477	145
okini3939	0:126d52039477	146	char SHT::measure(int &value, byte command)
okini3939	0:126d52039477	147	//----------------------------------------------------------------------------------
okini3939	0:126d52039477	148	// makes a measurement (humidity/temperature) with checksum
okini3939	0:126d52039477	149	{
okini3939	0:126d52039477	150	unsigned int i;
okini3939	0:126d52039477	151	byte msb;
okini3939	0:126d52039477	152	// byte checksum;
okini3939	0:126d52039477	153
okini3939	0:126d52039477	154	trans_start(); //transmission start
okini3939	0:126d52039477	155	if (write_byte(command)) return 1; // if command fails return
okini3939	0:126d52039477	156
okini3939	0:126d52039477	157	for (i=10000;i;i--) { //wait until sensor has finished the measurement
okini3939	0:126d52039477	158	wait_us(100);
okini3939	0:126d52039477	159	if (data==0) break;
okini3939	0:126d52039477	160	}
okini3939	0:126d52039477	161	if (data) return 1; // or timeout (~1 sec.) is reached !!
okini3939	0:126d52039477	162	msb = read_byte(send_ack); //read the first byte (MSB)
okini3939	0:126d52039477	163	value = msb*256 + read_byte(send_ack); //read the second byte (LSB)
okini3939	0:126d52039477	164	/* checksum= */
okini3939	0:126d52039477	165	(void)read_byte(no_ack); //read checksum
okini3939	0:126d52039477	166	return 0;
okini3939	0:126d52039477	167	}
okini3939	0:126d52039477	168
okini3939	0:126d52039477	169	void SHT::calculate()
okini3939	0:126d52039477	170	//----------------------------------------------------------------------------------------
okini3939	0:126d52039477	171	// calculates temperature [°C] and humidity [%RH]
okini3939	0:126d52039477	172	// input : hum [Ticks] (12 bit)
okini3939	0:126d52039477	173	// temp [Ticks] (14 bit)
okini3939	0:126d52039477	174	// output: humidity [%RH]
okini3939	0:126d52039477	175	// temperature [°C]
okini3939	0:126d52039477	176	{
okini3939	0:126d52039477	177	const float C1=-4.0; // for 12 Bit
okini3939	0:126d52039477	178	const float C2=+0.0405; // for 12 Bit
okini3939	0:126d52039477	179	const float C3=-0.0000028; // for 12 Bit
okini3939	0:126d52039477	180	//const float T1=+0.01; // for 14 Bit @ 5V
okini3939	0:126d52039477	181	//const float T2=+0.00008; // for 14 Bit @ 5V
okini3939	0:126d52039477	182
okini3939	0:126d52039477	183	float rh; // rh: Humidity [Ticks] 12 Bit
okini3939	0:126d52039477	184	float t; // t: Temperature [Ticks] 14 Bit
okini3939	0:126d52039477	185	//float rh_lin; // rh_lin: Humidity linear
okini3939	0:126d52039477	186	if (accuracy==SHT_low) {
okini3939	0:126d52039477	187	rh=hum*16; // rescale to high accuracy values - 8 to 12 bits
okini3939	0:126d52039477	188	t=temp*4; // and 12 to 14 bits
okini3939	0:126d52039477	189	} else {
okini3939	0:126d52039477	190	rh=hum;
okini3939	0:126d52039477	191	t=temp;
okini3939	0:126d52039477	192	}
okini3939	0:126d52039477	193
okini3939	0:126d52039477	194	temperature=t*0.01 - 40; //calc. temperature from ticks to [°C]
okini3939	0:126d52039477	195	humidity=C3rhrh + C2*rh + C1; //calc. humidity from ticks to [%RH]
okini3939	0:126d52039477	196	// =(temperature-25)(T1+T2rh)+rh_lin; //calc. temperature compensated humidity [%RH] (ignore as never >0.25%)
okini3939	0:126d52039477	197	if (humidity>100)humidity=100; //cut if the value is outside of
okini3939	0:126d52039477	198	if (humidity<0.1)humidity=0.1; //the physical possible range
okini3939	0:126d52039477	199	}
okini3939	0:126d52039477	200
okini3939	0:126d52039477	201	float SHT::get_temperature() { // get the most recent temp reading
okini3939	0:126d52039477	202	return temperature;
okini3939	0:126d52039477	203	}
okini3939	0:126d52039477	204
okini3939	0:126d52039477	205	float SHT::get_humidity() { // get the most recent humidity reading
okini3939	0:126d52039477	206	return humidity;
okini3939	0:126d52039477	207	}
okini3939	0:126d52039477	208
okini3939	0:126d52039477	209	float SHT::get_dewpoint() { // get the most recent dewpoint value
okini3939	0:126d52039477	210	return dewpoint;
okini3939	0:126d52039477	211	}
okini3939	0:126d52039477	212
okini3939	0:126d52039477	213	void SHT::update(SHT_acc acc) { // update stored values from sensor
okini3939	0:126d52039477	214	int error=0;
okini3939	0:126d52039477	215	connection_reset();
okini3939	0:126d52039477	216	if (acc!=accuracy) {
okini3939	0:126d52039477	217	accuracy=acc;
okini3939	0:126d52039477	218	error+=write_status((acc==SHT_low)?0x01:0x00); //set the status reg to high or low accuarcy
okini3939	0:126d52039477	219	}
okini3939	0:126d52039477	220	error+=measure(temp,com_measure_temp);
okini3939	0:126d52039477	221	error+=measure(hum,com_measure_humid);
okini3939	0:126d52039477	222	if (!error) calculate();
okini3939	0:126d52039477	223
okini3939	0:126d52039477	224	}

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Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	01 Dec 2010
Imports:	11
Forks:	0
Commits:	1
Dependents:	0
Dependencies:	5
Followers:	1

SHT_v1/SHT.cpp@0:126d52039477, 2010-12-01 (annotated)

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