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SHT_v1/SHT.cpp@2:920a4e65129d, 2010-10-12 (annotated)

Committer:: okini3939
Date:: Tue Oct 12 16:44:01 2010 +0000
Revision:: 2:920a4e65129d
Parent:: 0:6e444b317905

Who changed what in which revision?

User	Revision	Line number	New contents of line
okini3939	0:6e444b317905	1	/* mbed module to use a Sensirion SHT1x /SHT7x sensor
okini3939	0:6e444b317905	2	* Copyright (c) 2007-2009 Stephen McGarry
okini3939	0:6e444b317905	3	* Released under the MIT License: http://mbed.org/license/mit
okini3939	0:6e444b317905	4	*/
okini3939	0:6e444b317905	5
okini3939	0:6e444b317905	6	#include "SHT.h"
okini3939	0:6e444b317905	7
okini3939	0:6e444b317905	8	#include "mbed.h"
okini3939	0:6e444b317905	9
okini3939	0:6e444b317905	10	SHT::SHT(PinName p_sclk, PinName p_data, SHT_acc p_accuracy) : sclk(p_sclk), data(p_data), accuracy(p_accuracy) {
okini3939	0:6e444b317905	11	sclk=0;
okini3939	0:6e444b317905	12	data=0; // data pin will be used as open collector pin
okini3939	0:6e444b317905	13	data.mode(PullUp); // with the pull up internally active
okini3939	0:6e444b317905	14	data.input(); // with line released to go high
okini3939	0:6e444b317905	15	temperature = humidity = dewpoint=0.0f;
okini3939	0:6e444b317905	16	printf("constructor\n");
okini3939	0:6e444b317905	17	}
okini3939	0:6e444b317905	18
okini3939	0:6e444b317905	19	char SHT::write_byte(byte value)
okini3939	0:6e444b317905	20	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	21	// writes a byte on the Sensibus and checks the acknowledge
okini3939	0:6e444b317905	22	{
okini3939	0:6e444b317905	23	int i;
okini3939	0:6e444b317905	24	char error=0;
okini3939	0:6e444b317905	25
okini3939	0:6e444b317905	26	for (i=0x80;i>0;i/=2) { //shift bit for masking
okini3939	0:6e444b317905	27	if (i & value) data.input(); //masking value with i , write to SENSI-BUS
okini3939	0:6e444b317905	28	else data.output();
okini3939	0:6e444b317905	29	wait_us(1); //ensure sclk is low for min time
okini3939	0:6e444b317905	30	sclk=1; //clk for SENSI-BUS
okini3939	0:6e444b317905	31	wait_us(1); //pulsewith approx. 2 us
okini3939	0:6e444b317905	32	sclk=0;
okini3939	0:6e444b317905	33	}
okini3939	0:6e444b317905	34	data.input(); //release DATA-line
okini3939	0:6e444b317905	35	wait_us(1); //ensure sclk is low for min time
okini3939	0:6e444b317905	36	sclk=1; //clk #9 for ack
okini3939	0:6e444b317905	37	error=data; //check ack (DATA will be pulled down by SHT11)
okini3939	0:6e444b317905	38	wait_us(1);
okini3939	0:6e444b317905	39	sclk=0;
okini3939	0:6e444b317905	40	return error; //error=1 in case of no acknowledge
okini3939	0:6e444b317905	41	}
okini3939	0:6e444b317905	42
okini3939	0:6e444b317905	43	byte SHT::read_byte(bool send_ack)
okini3939	0:6e444b317905	44	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	45	// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
okini3939	0:6e444b317905	46	{
okini3939	0:6e444b317905	47	byte i,val=0;
okini3939	0:6e444b317905	48	data.input(); //release DATA-line
okini3939	0:6e444b317905	49	for (i=0x80;i>0;i/=2) { //shift bit for masking
okini3939	0:6e444b317905	50	wait_us(1);
okini3939	0:6e444b317905	51	sclk=1; //clk for SENSI-BUS
okini3939	0:6e444b317905	52	if (data) val=(val \| i); //read bit
okini3939	0:6e444b317905	53	wait_us(1);
okini3939	0:6e444b317905	54	sclk=0;
okini3939	0:6e444b317905	55	}
okini3939	0:6e444b317905	56	wait_us(1);
okini3939	0:6e444b317905	57	if (send_ack) data.output(); // if ack needed then drive data low
okini3939	0:6e444b317905	58	sclk=1; //clk #9 for ack
okini3939	0:6e444b317905	59	wait_us(1);
okini3939	0:6e444b317905	60	sclk=0;
okini3939	0:6e444b317905	61	data.input(); //release DATA-line
okini3939	0:6e444b317905	62	return val;
okini3939	0:6e444b317905	63	}
okini3939	0:6e444b317905	64
okini3939	0:6e444b317905	65	void SHT::trans_start(void)
okini3939	0:6e444b317905	66	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	67	// generates a transmission start
okini3939	0:6e444b317905	68	// _____ ________
okini3939	0:6e444b317905	69	// DATA: \|_______\|
okini3939	0:6e444b317905	70	// ___ ___
okini3939	0:6e444b317905	71	// SCK : ___\| \|___\| \|______
okini3939	0:6e444b317905	72	{
okini3939	0:6e444b317905	73	data.input();
okini3939	0:6e444b317905	74	sclk=0; //Initial state
okini3939	0:6e444b317905	75	wait_us(1);
okini3939	0:6e444b317905	76	sclk=1;
okini3939	0:6e444b317905	77	wait_us(1);
okini3939	0:6e444b317905	78	data.output(); // data low
okini3939	0:6e444b317905	79	wait_us(1);
okini3939	0:6e444b317905	80	sclk=0;
okini3939	0:6e444b317905	81	wait_us(1);
okini3939	0:6e444b317905	82	sclk=1;
okini3939	0:6e444b317905	83	wait_us(1);
okini3939	0:6e444b317905	84	data.input(); // allow data to high
okini3939	0:6e444b317905	85	wait_us(1);
okini3939	0:6e444b317905	86	sclk=0;
okini3939	0:6e444b317905	87	wait_us(1);
okini3939	0:6e444b317905	88	}
okini3939	0:6e444b317905	89
okini3939	0:6e444b317905	90	void SHT::connection_reset(void)
okini3939	0:6e444b317905	91	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	92	// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
okini3939	0:6e444b317905	93	// _____________________________________________________ ________
okini3939	0:6e444b317905	94	// DATA: \|_______\|
okini3939	0:6e444b317905	95	// _ _ _ _ _ _ _ _ _ ___ ___
okini3939	0:6e444b317905	96	// SCK : __\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|______\| \|___\| \|______
okini3939	0:6e444b317905	97	{
okini3939	0:6e444b317905	98	int i;
okini3939	0:6e444b317905	99	data.input(); // allow data high
okini3939	0:6e444b317905	100	sclk=0; // and clk low
okini3939	0:6e444b317905	101	for (i=0;i<9;i++) { // 9 SCK cycles
okini3939	0:6e444b317905	102	wait_us(1);
okini3939	0:6e444b317905	103	sclk=1;
okini3939	0:6e444b317905	104	wait_us(1);
okini3939	0:6e444b317905	105	sclk=0;
okini3939	0:6e444b317905	106	}
okini3939	0:6e444b317905	107	}
okini3939	0:6e444b317905	108	char SHT::soft_reset(void)
okini3939	0:6e444b317905	109	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	110	// resets the sensor by a softreset
okini3939	0:6e444b317905	111	{
okini3939	0:6e444b317905	112	char error=0;
okini3939	0:6e444b317905	113	SHT::connection_reset(); //reset communication
okini3939	0:6e444b317905	114	trans_start();
okini3939	0:6e444b317905	115	error+=write_byte(com_reset); //send RESET-command to sensor
okini3939	0:6e444b317905	116	return error; //error=1 in case of no response form the sensor
okini3939	0:6e444b317905	117	}
okini3939	0:6e444b317905	118
okini3939	0:6e444b317905	119	char SHT::read_status(byte &value)
okini3939	0:6e444b317905	120	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	121	// reads the status register with checksum (8-bit)
okini3939	0:6e444b317905	122	{
okini3939	0:6e444b317905	123	//byte checksum;
okini3939	0:6e444b317905	124
okini3939	0:6e444b317905	125	char error=0;
okini3939	0:6e444b317905	126	trans_start(); //transmission start
okini3939	0:6e444b317905	127	error=write_byte(com_read_status_reg); //send command to sensor
okini3939	0:6e444b317905	128	value=read_byte(send_ack); //read status register (8-bit)
okini3939	0:6e444b317905	129	/* checksum= */
okini3939	0:6e444b317905	130	(void)read_byte(no_ack); //read checksum (8-bit)
okini3939	0:6e444b317905	131	// check the checksum ??
okini3939	0:6e444b317905	132	return error; //error=1 in case of no response form the sensor
okini3939	0:6e444b317905	133	}
okini3939	0:6e444b317905	134
okini3939	0:6e444b317905	135	char SHT::write_status(byte value)
okini3939	0:6e444b317905	136	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	137	// writes the status register (8-bit)
okini3939	0:6e444b317905	138	{
okini3939	0:6e444b317905	139	char error=0;
okini3939	0:6e444b317905	140	trans_start(); //transmission start
okini3939	0:6e444b317905	141	error+=write_byte(com_write_status_reg); //send command to sensor
okini3939	0:6e444b317905	142	error+=write_byte(value); //send value of status register
okini3939	0:6e444b317905	143	return error; //error>=1 in case of no response form the sensor
okini3939	0:6e444b317905	144	}
okini3939	0:6e444b317905	145
okini3939	0:6e444b317905	146	char SHT::measure(int &value, byte command)
okini3939	0:6e444b317905	147	//----------------------------------------------------------------------------------
okini3939	0:6e444b317905	148	// makes a measurement (humidity/temperature) with checksum
okini3939	0:6e444b317905	149	{
okini3939	0:6e444b317905	150	unsigned int i;
okini3939	0:6e444b317905	151	byte msb;
okini3939	0:6e444b317905	152	// byte checksum;
okini3939	0:6e444b317905	153
okini3939	0:6e444b317905	154	trans_start(); //transmission start
okini3939	0:6e444b317905	155	if (write_byte(command)) return 1; // if command fails return
okini3939	0:6e444b317905	156
okini3939	0:6e444b317905	157	for (i=10000;i;i--) { //wait until sensor has finished the measurement
okini3939	0:6e444b317905	158	wait_us(100);
okini3939	0:6e444b317905	159	if (data==0) break;
okini3939	0:6e444b317905	160	}
okini3939	0:6e444b317905	161	if (data) return 1; // or timeout (~1 sec.) is reached !!
okini3939	0:6e444b317905	162	msb = read_byte(send_ack); //read the first byte (MSB)
okini3939	0:6e444b317905	163	value = msb*256 + read_byte(send_ack); //read the second byte (LSB)
okini3939	0:6e444b317905	164	/* checksum= */
okini3939	0:6e444b317905	165	(void)read_byte(no_ack); //read checksum
okini3939	0:6e444b317905	166	return 0;
okini3939	0:6e444b317905	167	}
okini3939	0:6e444b317905	168
okini3939	0:6e444b317905	169	void SHT::calculate()
okini3939	0:6e444b317905	170	//----------------------------------------------------------------------------------------
okini3939	0:6e444b317905	171	// calculates temperature [°C] and humidity [%RH]
okini3939	0:6e444b317905	172	// input : hum [Ticks] (12 bit)
okini3939	0:6e444b317905	173	// temp [Ticks] (14 bit)
okini3939	0:6e444b317905	174	// output: humidity [%RH]
okini3939	0:6e444b317905	175	// temperature [°C]
okini3939	0:6e444b317905	176	{
okini3939	0:6e444b317905	177	const float C1=-4.0; // for 12 Bit
okini3939	0:6e444b317905	178	const float C2=+0.0405; // for 12 Bit
okini3939	0:6e444b317905	179	const float C3=-0.0000028; // for 12 Bit
okini3939	0:6e444b317905	180	//const float T1=+0.01; // for 14 Bit @ 5V
okini3939	0:6e444b317905	181	//const float T2=+0.00008; // for 14 Bit @ 5V
okini3939	0:6e444b317905	182
okini3939	0:6e444b317905	183	float rh; // rh: Humidity [Ticks] 12 Bit
okini3939	0:6e444b317905	184	float t; // t: Temperature [Ticks] 14 Bit
okini3939	0:6e444b317905	185	//float rh_lin; // rh_lin: Humidity linear
okini3939	0:6e444b317905	186	if (accuracy==SHT_low) {
okini3939	0:6e444b317905	187	rh=hum*16; // rescale to high accuracy values - 8 to 12 bits
okini3939	0:6e444b317905	188	t=temp*4; // and 12 to 14 bits
okini3939	0:6e444b317905	189	} else {
okini3939	0:6e444b317905	190	rh=hum;
okini3939	0:6e444b317905	191	t=temp;
okini3939	0:6e444b317905	192	}
okini3939	0:6e444b317905	193
okini3939	0:6e444b317905	194	temperature=t*0.01 - 40; //calc. temperature from ticks to [°C]
okini3939	0:6e444b317905	195	humidity=C3rhrh + C2*rh + C1; //calc. humidity from ticks to [%RH]
okini3939	0:6e444b317905	196	// =(temperature-25)(T1+T2rh)+rh_lin; //calc. temperature compensated humidity [%RH] (ignore as never >0.25%)
okini3939	0:6e444b317905	197	if (humidity>100)humidity=100; //cut if the value is outside of
okini3939	0:6e444b317905	198	if (humidity<0.1)humidity=0.1; //the physical possible range
okini3939	0:6e444b317905	199	}
okini3939	0:6e444b317905	200
okini3939	0:6e444b317905	201	float SHT::get_temperature() { // get the most recent temp reading
okini3939	0:6e444b317905	202	return temperature;
okini3939	0:6e444b317905	203	}
okini3939	0:6e444b317905	204
okini3939	0:6e444b317905	205	float SHT::get_humidity() { // get the most recent humidity reading
okini3939	0:6e444b317905	206	return humidity;
okini3939	0:6e444b317905	207	}
okini3939	0:6e444b317905	208
okini3939	0:6e444b317905	209	float SHT::get_dewpoint() { // get the most recent dewpoint value
okini3939	0:6e444b317905	210	return dewpoint;
okini3939	0:6e444b317905	211	}
okini3939	0:6e444b317905	212
okini3939	0:6e444b317905	213	void SHT::update(SHT_acc acc) { // update stored values from sensor
okini3939	0:6e444b317905	214	int error=0;
okini3939	0:6e444b317905	215	connection_reset();
okini3939	0:6e444b317905	216	if (acc!=accuracy) {
okini3939	0:6e444b317905	217	accuracy=acc;
okini3939	0:6e444b317905	218	error+=write_status((acc==SHT_low)?0x01:0x00); //set the status reg to high or low accuarcy
okini3939	0:6e444b317905	219	}
okini3939	0:6e444b317905	220	error+=measure(temp,com_measure_temp);
okini3939	0:6e444b317905	221	error+=measure(hum,com_measure_humid);
okini3939	0:6e444b317905	222	if (!error) calculate();
okini3939	0:6e444b317905	223
okini3939	0:6e444b317905	224	}

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Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	27 Sep 2010
Imports:	48
Forks:	0
Commits:	3
Dependents:	0
Dependencies:	1
Followers:	3

SHT_v1/SHT.cpp@2:920a4e65129d, 2010-10-12 (annotated)

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