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SHT_v1/SHT.cpp@0:10bcaa7c2253, 2010-10-26 (annotated)

Committer:: okini3939
Date:: Tue Oct 26 17:19:28 2010 +0000
Revision:: 0:10bcaa7c2253

Who changed what in which revision?

User	Revision	Line number	New contents of line
okini3939	0:10bcaa7c2253	1	/* mbed module to use a Sensirion SHT1x /SHT7x sensor
okini3939	0:10bcaa7c2253	2	* Copyright (c) 2007-2009 Stephen McGarry
okini3939	0:10bcaa7c2253	3	* Released under the MIT License: http://mbed.org/license/mit
okini3939	0:10bcaa7c2253	4	*/
okini3939	0:10bcaa7c2253	5
okini3939	0:10bcaa7c2253	6	#include "SHT.h"
okini3939	0:10bcaa7c2253	7
okini3939	0:10bcaa7c2253	8	#include "mbed.h"
okini3939	0:10bcaa7c2253	9
okini3939	0:10bcaa7c2253	10	SHT::SHT(PinName p_sclk, PinName p_data, SHT_acc p_accuracy) : sclk(p_sclk), data(p_data), accuracy(p_accuracy) {
okini3939	0:10bcaa7c2253	11	sclk=0;
okini3939	0:10bcaa7c2253	12	data=0; // data pin will be used as open collector pin
okini3939	0:10bcaa7c2253	13	data.mode(PullUp); // with the pull up internally active
okini3939	0:10bcaa7c2253	14	data.input(); // with line released to go high
okini3939	0:10bcaa7c2253	15	temperature = humidity = dewpoint=0.0f;
okini3939	0:10bcaa7c2253	16	printf("constructor\n");
okini3939	0:10bcaa7c2253	17	}
okini3939	0:10bcaa7c2253	18
okini3939	0:10bcaa7c2253	19	char SHT::write_byte(byte value)
okini3939	0:10bcaa7c2253	20	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	21	// writes a byte on the Sensibus and checks the acknowledge
okini3939	0:10bcaa7c2253	22	{
okini3939	0:10bcaa7c2253	23	int i;
okini3939	0:10bcaa7c2253	24	char error=0;
okini3939	0:10bcaa7c2253	25
okini3939	0:10bcaa7c2253	26	for (i=0x80;i>0;i/=2) { //shift bit for masking
okini3939	0:10bcaa7c2253	27	if (i & value) data.input(); //masking value with i , write to SENSI-BUS
okini3939	0:10bcaa7c2253	28	else data.output();
okini3939	0:10bcaa7c2253	29	wait_us(1); //ensure sclk is low for min time
okini3939	0:10bcaa7c2253	30	sclk=1; //clk for SENSI-BUS
okini3939	0:10bcaa7c2253	31	wait_us(1); //pulsewith approx. 2 us
okini3939	0:10bcaa7c2253	32	sclk=0;
okini3939	0:10bcaa7c2253	33	}
okini3939	0:10bcaa7c2253	34	data.input(); //release DATA-line
okini3939	0:10bcaa7c2253	35	wait_us(1); //ensure sclk is low for min time
okini3939	0:10bcaa7c2253	36	sclk=1; //clk #9 for ack
okini3939	0:10bcaa7c2253	37	error=data; //check ack (DATA will be pulled down by SHT11)
okini3939	0:10bcaa7c2253	38	wait_us(1);
okini3939	0:10bcaa7c2253	39	sclk=0;
okini3939	0:10bcaa7c2253	40	return error; //error=1 in case of no acknowledge
okini3939	0:10bcaa7c2253	41	}
okini3939	0:10bcaa7c2253	42
okini3939	0:10bcaa7c2253	43	byte SHT::read_byte(bool send_ack)
okini3939	0:10bcaa7c2253	44	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	45	// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
okini3939	0:10bcaa7c2253	46	{
okini3939	0:10bcaa7c2253	47	byte i,val=0;
okini3939	0:10bcaa7c2253	48	data.input(); //release DATA-line
okini3939	0:10bcaa7c2253	49	for (i=0x80;i>0;i/=2) { //shift bit for masking
okini3939	0:10bcaa7c2253	50	wait_us(1);
okini3939	0:10bcaa7c2253	51	sclk=1; //clk for SENSI-BUS
okini3939	0:10bcaa7c2253	52	if (data) val=(val \| i); //read bit
okini3939	0:10bcaa7c2253	53	wait_us(1);
okini3939	0:10bcaa7c2253	54	sclk=0;
okini3939	0:10bcaa7c2253	55	}
okini3939	0:10bcaa7c2253	56	wait_us(1);
okini3939	0:10bcaa7c2253	57	if (send_ack) data.output(); // if ack needed then drive data low
okini3939	0:10bcaa7c2253	58	sclk=1; //clk #9 for ack
okini3939	0:10bcaa7c2253	59	wait_us(1);
okini3939	0:10bcaa7c2253	60	sclk=0;
okini3939	0:10bcaa7c2253	61	data.input(); //release DATA-line
okini3939	0:10bcaa7c2253	62	return val;
okini3939	0:10bcaa7c2253	63	}
okini3939	0:10bcaa7c2253	64
okini3939	0:10bcaa7c2253	65	void SHT::trans_start(void)
okini3939	0:10bcaa7c2253	66	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	67	// generates a transmission start
okini3939	0:10bcaa7c2253	68	// _____ ________
okini3939	0:10bcaa7c2253	69	// DATA: \|_______\|
okini3939	0:10bcaa7c2253	70	// ___ ___
okini3939	0:10bcaa7c2253	71	// SCK : ___\| \|___\| \|______
okini3939	0:10bcaa7c2253	72	{
okini3939	0:10bcaa7c2253	73	data.input();
okini3939	0:10bcaa7c2253	74	sclk=0; //Initial state
okini3939	0:10bcaa7c2253	75	wait_us(1);
okini3939	0:10bcaa7c2253	76	sclk=1;
okini3939	0:10bcaa7c2253	77	wait_us(1);
okini3939	0:10bcaa7c2253	78	data.output(); // data low
okini3939	0:10bcaa7c2253	79	wait_us(1);
okini3939	0:10bcaa7c2253	80	sclk=0;
okini3939	0:10bcaa7c2253	81	wait_us(1);
okini3939	0:10bcaa7c2253	82	sclk=1;
okini3939	0:10bcaa7c2253	83	wait_us(1);
okini3939	0:10bcaa7c2253	84	data.input(); // allow data to high
okini3939	0:10bcaa7c2253	85	wait_us(1);
okini3939	0:10bcaa7c2253	86	sclk=0;
okini3939	0:10bcaa7c2253	87	wait_us(1);
okini3939	0:10bcaa7c2253	88	}
okini3939	0:10bcaa7c2253	89
okini3939	0:10bcaa7c2253	90	void SHT::connection_reset(void)
okini3939	0:10bcaa7c2253	91	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	92	// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
okini3939	0:10bcaa7c2253	93	// _____________________________________________________ ________
okini3939	0:10bcaa7c2253	94	// DATA: \|_______\|
okini3939	0:10bcaa7c2253	95	// _ _ _ _ _ _ _ _ _ ___ ___
okini3939	0:10bcaa7c2253	96	// SCK : __\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|__\| \|______\| \|___\| \|______
okini3939	0:10bcaa7c2253	97	{
okini3939	0:10bcaa7c2253	98	int i;
okini3939	0:10bcaa7c2253	99	data.input(); // allow data high
okini3939	0:10bcaa7c2253	100	sclk=0; // and clk low
okini3939	0:10bcaa7c2253	101	for (i=0;i<9;i++) { // 9 SCK cycles
okini3939	0:10bcaa7c2253	102	wait_us(1);
okini3939	0:10bcaa7c2253	103	sclk=1;
okini3939	0:10bcaa7c2253	104	wait_us(1);
okini3939	0:10bcaa7c2253	105	sclk=0;
okini3939	0:10bcaa7c2253	106	}
okini3939	0:10bcaa7c2253	107	}
okini3939	0:10bcaa7c2253	108	char SHT::soft_reset(void)
okini3939	0:10bcaa7c2253	109	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	110	// resets the sensor by a softreset
okini3939	0:10bcaa7c2253	111	{
okini3939	0:10bcaa7c2253	112	char error=0;
okini3939	0:10bcaa7c2253	113	SHT::connection_reset(); //reset communication
okini3939	0:10bcaa7c2253	114	trans_start();
okini3939	0:10bcaa7c2253	115	error+=write_byte(com_reset); //send RESET-command to sensor
okini3939	0:10bcaa7c2253	116	return error; //error=1 in case of no response form the sensor
okini3939	0:10bcaa7c2253	117	}
okini3939	0:10bcaa7c2253	118
okini3939	0:10bcaa7c2253	119	char SHT::read_status(byte &value)
okini3939	0:10bcaa7c2253	120	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	121	// reads the status register with checksum (8-bit)
okini3939	0:10bcaa7c2253	122	{
okini3939	0:10bcaa7c2253	123	//byte checksum;
okini3939	0:10bcaa7c2253	124
okini3939	0:10bcaa7c2253	125	char error=0;
okini3939	0:10bcaa7c2253	126	trans_start(); //transmission start
okini3939	0:10bcaa7c2253	127	error=write_byte(com_read_status_reg); //send command to sensor
okini3939	0:10bcaa7c2253	128	value=read_byte(send_ack); //read status register (8-bit)
okini3939	0:10bcaa7c2253	129	/* checksum= */
okini3939	0:10bcaa7c2253	130	(void)read_byte(no_ack); //read checksum (8-bit)
okini3939	0:10bcaa7c2253	131	// check the checksum ??
okini3939	0:10bcaa7c2253	132	return error; //error=1 in case of no response form the sensor
okini3939	0:10bcaa7c2253	133	}
okini3939	0:10bcaa7c2253	134
okini3939	0:10bcaa7c2253	135	char SHT::write_status(byte value)
okini3939	0:10bcaa7c2253	136	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	137	// writes the status register (8-bit)
okini3939	0:10bcaa7c2253	138	{
okini3939	0:10bcaa7c2253	139	char error=0;
okini3939	0:10bcaa7c2253	140	trans_start(); //transmission start
okini3939	0:10bcaa7c2253	141	error+=write_byte(com_write_status_reg); //send command to sensor
okini3939	0:10bcaa7c2253	142	error+=write_byte(value); //send value of status register
okini3939	0:10bcaa7c2253	143	return error; //error>=1 in case of no response form the sensor
okini3939	0:10bcaa7c2253	144	}
okini3939	0:10bcaa7c2253	145
okini3939	0:10bcaa7c2253	146	char SHT::measure(int &value, byte command)
okini3939	0:10bcaa7c2253	147	//----------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	148	// makes a measurement (humidity/temperature) with checksum
okini3939	0:10bcaa7c2253	149	{
okini3939	0:10bcaa7c2253	150	unsigned int i;
okini3939	0:10bcaa7c2253	151	byte msb;
okini3939	0:10bcaa7c2253	152	// byte checksum;
okini3939	0:10bcaa7c2253	153
okini3939	0:10bcaa7c2253	154	trans_start(); //transmission start
okini3939	0:10bcaa7c2253	155	if (write_byte(command)) return 1; // if command fails return
okini3939	0:10bcaa7c2253	156
okini3939	0:10bcaa7c2253	157	for (i=10000;i;i--) { //wait until sensor has finished the measurement
okini3939	0:10bcaa7c2253	158	wait_us(100);
okini3939	0:10bcaa7c2253	159	if (data==0) break;
okini3939	0:10bcaa7c2253	160	}
okini3939	0:10bcaa7c2253	161	if (data) return 1; // or timeout (~1 sec.) is reached !!
okini3939	0:10bcaa7c2253	162	msb = read_byte(send_ack); //read the first byte (MSB)
okini3939	0:10bcaa7c2253	163	value = msb*256 + read_byte(send_ack); //read the second byte (LSB)
okini3939	0:10bcaa7c2253	164	/* checksum= */
okini3939	0:10bcaa7c2253	165	(void)read_byte(no_ack); //read checksum
okini3939	0:10bcaa7c2253	166	return 0;
okini3939	0:10bcaa7c2253	167	}
okini3939	0:10bcaa7c2253	168
okini3939	0:10bcaa7c2253	169	void SHT::calculate()
okini3939	0:10bcaa7c2253	170	//----------------------------------------------------------------------------------------
okini3939	0:10bcaa7c2253	171	// calculates temperature [°C] and humidity [%RH]
okini3939	0:10bcaa7c2253	172	// input : hum [Ticks] (12 bit)
okini3939	0:10bcaa7c2253	173	// temp [Ticks] (14 bit)
okini3939	0:10bcaa7c2253	174	// output: humidity [%RH]
okini3939	0:10bcaa7c2253	175	// temperature [°C]
okini3939	0:10bcaa7c2253	176	{
okini3939	0:10bcaa7c2253	177	const float C1=-4.0; // for 12 Bit
okini3939	0:10bcaa7c2253	178	const float C2=+0.0405; // for 12 Bit
okini3939	0:10bcaa7c2253	179	const float C3=-0.0000028; // for 12 Bit
okini3939	0:10bcaa7c2253	180	//const float T1=+0.01; // for 14 Bit @ 5V
okini3939	0:10bcaa7c2253	181	//const float T2=+0.00008; // for 14 Bit @ 5V
okini3939	0:10bcaa7c2253	182
okini3939	0:10bcaa7c2253	183	float rh; // rh: Humidity [Ticks] 12 Bit
okini3939	0:10bcaa7c2253	184	float t; // t: Temperature [Ticks] 14 Bit
okini3939	0:10bcaa7c2253	185	//float rh_lin; // rh_lin: Humidity linear
okini3939	0:10bcaa7c2253	186	if (accuracy==SHT_low) {
okini3939	0:10bcaa7c2253	187	rh=hum*16; // rescale to high accuracy values - 8 to 12 bits
okini3939	0:10bcaa7c2253	188	t=temp*4; // and 12 to 14 bits
okini3939	0:10bcaa7c2253	189	} else {
okini3939	0:10bcaa7c2253	190	rh=hum;
okini3939	0:10bcaa7c2253	191	t=temp;
okini3939	0:10bcaa7c2253	192	}
okini3939	0:10bcaa7c2253	193
okini3939	0:10bcaa7c2253	194	temperature=t*0.01 - 40; //calc. temperature from ticks to [°C]
okini3939	0:10bcaa7c2253	195	humidity=C3rhrh + C2*rh + C1; //calc. humidity from ticks to [%RH]
okini3939	0:10bcaa7c2253	196	// =(temperature-25)(T1+T2rh)+rh_lin; //calc. temperature compensated humidity [%RH] (ignore as never >0.25%)
okini3939	0:10bcaa7c2253	197	if (humidity>100)humidity=100; //cut if the value is outside of
okini3939	0:10bcaa7c2253	198	if (humidity<0.1)humidity=0.1; //the physical possible range
okini3939	0:10bcaa7c2253	199	}
okini3939	0:10bcaa7c2253	200
okini3939	0:10bcaa7c2253	201	float SHT::get_temperature() { // get the most recent temp reading
okini3939	0:10bcaa7c2253	202	return temperature;
okini3939	0:10bcaa7c2253	203	}
okini3939	0:10bcaa7c2253	204
okini3939	0:10bcaa7c2253	205	float SHT::get_humidity() { // get the most recent humidity reading
okini3939	0:10bcaa7c2253	206	return humidity;
okini3939	0:10bcaa7c2253	207	}
okini3939	0:10bcaa7c2253	208
okini3939	0:10bcaa7c2253	209	float SHT::get_dewpoint() { // get the most recent dewpoint value
okini3939	0:10bcaa7c2253	210	return dewpoint;
okini3939	0:10bcaa7c2253	211	}
okini3939	0:10bcaa7c2253	212
okini3939	0:10bcaa7c2253	213	void SHT::update(SHT_acc acc) { // update stored values from sensor
okini3939	0:10bcaa7c2253	214	int error=0;
okini3939	0:10bcaa7c2253	215	connection_reset();
okini3939	0:10bcaa7c2253	216	if (acc!=accuracy) {
okini3939	0:10bcaa7c2253	217	accuracy=acc;
okini3939	0:10bcaa7c2253	218	error+=write_status((acc==SHT_low)?0x01:0x00); //set the status reg to high or low accuarcy
okini3939	0:10bcaa7c2253	219	}
okini3939	0:10bcaa7c2253	220	error+=measure(temp,com_measure_temp);
okini3939	0:10bcaa7c2253	221	error+=measure(hum,com_measure_humid);
okini3939	0:10bcaa7c2253	222	if (!error) calculate();
okini3939	0:10bcaa7c2253	223
okini3939	0:10bcaa7c2253	224	}

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Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	26 Oct 2010
Imports:	8
Forks:	0
Commits:	1
Dependents:	0
Dependencies:	4
Followers:	1

SHT_v1/SHT.cpp@0:10bcaa7c2253, 2010-10-26 (annotated)

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