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The Si7021 I2C Humidity and Temperature Sensor is a monolithic CMOS IC integrating humidity and temperature sensor elements, an analog-to-digital converter, signal processing, calibration data, and an I2C Interface. The patented use of industry-standard, low-K polymeric dielectrics for sensing humidity enables the construction of low-power, monolithic CMOS Sensor ICs with low drift and hysteresis, and excellent long term stability
Features
- Relative Humidity Sensor:
- Si7013/21: ± 3% RH (maximum) @ 0-80% RH
- Si7020: ± 4% RH (maximum) @ 0-80% RH
- Si7006: ± 5% RH (maximum) @ 0-80% RH
- Temperature Sensor:
- Si7013/20/21: ±0.4°C accuracy (maximum) @ -10 to +85°C
- Si7006: ±1.0°C accuracy (maximum) @ -10 to +85°C
- 0 to 100% RH operating range
- Up to -40 to +125°C operating range
- Wide operating voltage range (1.9 to 3.6V)
- Low Power Consumption: 2.2µW average power at 3.3V and 1 sample per second
- I2C host interface
- Integrated on-chip heater
- 3mm x 3mm QFN package
- Excellent long term stability
- Factory calibrated
- Optional factory-installed filter/cover
- Lifetime protection during reflow and in operation
- Protects against contamination from dust, dirt, household chemicals and other liquids
- AEC-Q100 automotive qualified (Si7013/20/21)
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Connection
Must use 3v3 for Vin
| Arduino Pins |
Module Pins |
| 3v3 |
Vin |
| Gnd |
Gnd |
| SDA |
SDA |
| SCL |
SCL |
Code
#include <Wire.h>
const int ADDR =0x40;
int X0,X1,Y0,Y1,Y2,Y3;
double X,Y,X_out,Y_out1,Y_out2;
void setup()
{
Serial.begin(9600);
Wire.begin();
delay(100);
Wire.beginTransmission(ADDR);
Wire.endTransmission();
}
void loop()
{
/**Send command of initiating temperature measurement**/
Wire.beginTransmission(ADDR);
Wire.write(0xE3);
Wire.endTransmission();
Serial.print("Temp");
Serial.print("\t");
Serial.println("Humidity");
/**Read data of temperature**/
Wire.requestFrom(ADDR,2);
if(Wire.available()<=2);
{
X0 = Wire.read();
X1 = Wire.read();
X0 = X0<<8;
X_out = X0+X1;
}
/**Calculate and display temperature**/
X=(175.72*X_out)/65536;
X=X-46.85;
Serial.print(X);
Serial.print("C");
Serial.print("\t");
/**Send command of initiating relative humidity measurement**/
Wire.beginTransmission(ADDR);
Wire.write(0xE5);
Wire.endTransmission();
/**Read data of relative humidity**/
Wire.requestFrom(ADDR,2);
if(Wire.available()<=2);
{
Y0 = Wire.read();
Y2=Y0/100;
Y0=Y0%100;
Y1 = Wire.read();
Y_out1 = Y2*25600;
Y_out2 = Y0*256+Y1;
}
/**Calculate and display relative humidity**/
Y_out1 = (125*Y_out1)/65536;
Y_out2 = (125*Y_out2)/65536;
Y = Y_out1+Y_out2;
Y=Y-6;
Serial.print(Y);
Serial.println("%");
delay(300);
Serial.println();
delay(1000);
}
Output
Open the serial monitor, you should see something like this
Temp Humidity
23.12C 52.83%
Temp Humidity
24.04C 53.13%
Temp Humidity
26.28C 53.83%
Temp Humidity
27.42C 54.57%
Temp Humidity
28.27C 55.32%
Temp Humidity
27.94C 56.11%
Links
Humidity Temperature Sensor Breakout Barometric Pressure SI7021 for Arduino GY-21
The SHT1x digital humidity sensor is a reflow solderable sensor. The SHT1x series consists of a low-cost version with the SHT10 humidity sensor, a standard version with the SHT11 humidity sensor, and a high-end version with the SHT15 humidity sensor. As with every other Sensirion sensor type from the SHTxx humidity sensor family, they are fully calibrated and provide a digital output.
The humidity sensors are seamlessly coupled to a 14-bit-analog-to-digital converter and a serial interface circuit. This results in superior signal quality, a fast response time, and insensitivity to external disturbances (EMC).
One thing to note is that these sensors have been effectively replaced by others in sensirion’s range such as the SHT31 but they still work and have good performance for hobbyists
Layout
Code
You need to install the library from – https://github.com/practicalarduino/SHT1x
This is the built in example
#include <SHT1x.h>
// Specify data and clock connections and instantiate SHT1x object
#define dataPin 10
#define clockPin 11
SHT1x sht1x(dataPin, clockPin);
void setup()
{
Serial.begin(38400); // Open serial connection to report values to host
Serial.println("Starting up");
}
void loop()
{
float temp_c;
float temp_f;
float humidity;
// Read values from the sensor
temp_c = sht1x.readTemperatureC();
temp_f = sht1x.readTemperatureF();
humidity = sht1x.readHumidity();
// Print the values to the serial port
Serial.print("Temperature: ");
Serial.print(temp_c, DEC);
Serial.print("C / ");
Serial.print(temp_f, DEC);
Serial.print("F. Humidity: ");
Serial.print(humidity);
Serial.println("%");
delay(2000);
}
Testing
Open the serial monitor , all going well you should see something like this
Starting up
Temperature: 21.9199981689C / 71.5639953613F. Humidity: 47.88%
Temperature: 21.9499969482C / 71.5999984741F. Humidity: 47.88%
Temperature: 21.9499969482C / 71.5819931030F. Humidity: 47.85%
Links
SHT11 Digital Temperature and Humidity Sensor,Single bus output temperature and humidity module
The PCF8563 is a CMOS Real-Time Clock (RTC) and calendar optimized for low power consumption. A programmable clock output, interrupt output, and voltage-low detector are also provided. All addresses and data are transferred serially via a two-line bidirectional I²C-bus. Maximum bus speed is 400 kbit/s.
This is an easy to use module for this device
- Provides year, month, day, weekday, hours, minutes, and seconds based on a 32.768 kHz quartz crystal
- Century flag
- Clock operating voltage: 1.0 V to 5.5 V at room temperature
- Low backup current; typical 0.25 μA at VDD = 3.0 V and Tamb = 25 °C
- 400 kHz two-wire I²C-bus interface (at VDD = 1.8 V to 5.5 V)
- Programmable clock output for peripheral devices (32.768 kHz, 1.024 kHz, 32 Hz, and 1 Hz)
- Alarm and timer functions
- Integrated oscillator capacitor
- Internal Power-On Reset (POR)
- I²C-bus slave address: read A3h and write A2h
- Open-drain interrupt pin
This is the schematic for a typical module
 pcf8563 schematic Here is how to connect the module to your Arduino
Connection
| Arduino Pin |
Module Pin |
| 5v |
Vcc |
| GND |
Gnd |
| A5 |
SCL |
| A4 |
SDA |
Code
You do not need a library but I downloaded the library from https://bitbucket.org/orbitalair/arduino_rtc_pcf8563/downloads
This is one of the basic examples
/* Demonstration of Rtc_Pcf8563 Alarms.
*
* The Pcf8563 has an interrupt output, Pin3.
* Pull Pin3 HIGH with a resistor, I used a 10kohm to 5v.
* I used a RBBB with Arduino IDE, the pins are mapped a
* bit differently. Change for your hw.
* SCK - A5, SDA - A4, INT - D3/INT1
*
* After loading and starting the sketch, use the serial monitor
* to see the clock output.
*
* setup: see Pcf8563 data sheet.
* 1x 10Kohm pullup on Pin3 INT
* No pullups on Pin5 or Pin6 (I2C internals used)
* 1x 0.1pf on power
* 1x 32khz chrystal
*
* Joe Robertson, jmr
* orbitalair@bellsouth.net
*/
#include <Wire.h>
#include <Rtc_Pcf8563.h>
/* get a real time clock object */
Rtc_Pcf8563 rtc;
/* a flag for the interrupt */
volatile int alarm_flag=0;
/* the interrupt service routine */
void blink()
{
alarm_flag=1;
}
void setup()
{
pinMode(3, INPUT); // set pin to input
digitalWrite(3, HIGH); // turn on pullup resistors
Serial.begin(9600);
/* setup int on pin 3 of arduino */
attachInterrupt(1, blink, FALLING);
/* clear out all the registers */
rtc.initClock();
/* set a time to start with.
* day, weekday, month, century, year */
rtc.setDate(14, 6, 3, 0, 10);
/* hr, min, sec */
rtc.setTime(1, 15, 40);
/* set an alarm for 20 secs later...
* alarm pin goes low when match occurs
* this triggers the interrupt routine
* min, hr, day, weekday
* 99 = no alarm value to be set
*/
rtc.setAlarm(16, 99, 99, 99);
}
void loop()
{
/* each sec update the display */
Serial.print(rtc.formatTime());
Serial.print(" ");
Serial.print(rtc.formatDate());
Serial.print(" 0x");
Serial.print(rtc.getStatus2(), HEX);
Serial.print("\r\n");
delay(1000);
if (alarm_flag==1){
clr_alarm();
}
}
void clr_alarm()
{
detachInterrupt(1);
Serial.print("blink!\r\n");
rtc.clearAlarm();
delay(1000);
alarm_flag=0;
attachInterrupt(1, blink, FALLING);
}
Links
PCF8563 RTC Board PCF8563T CMOS Real-time Clock/Calendar Development Module
The DS3231 is a low-cost, extremely accurate I2C real-time clock (RTC) with an integrated temperature-compensated crystal oscillator (TCXO) and crystal.
The device incorporates a battery input, and maintains accurate timekeeping when main power to the device is interrupted.
 ds3231 Features
Highly Accurate RTC Completely Manages All Timekeeping Functions
Real-Time Clock Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the Week, and Year, with Leap-Year Compensation Valid Up to 2100
Accuracy ±2ppm from 0°C to +40°C
Accuracy ±3.5ppm from -40°C to +85°C
Digital Temp Sensor Output: ±3°C Accuracy
Two Time-of-Day Alarms
Programmable Square-Wave Output Signal
Simple Serial Interface Connects to Most Microcontrollers
Fast (400kHz) I2C Interface
Battery-Backup Input for Continuous Timekeeping
Low Power Operation Extends Battery-Backup Run Time
3.3V Operation
Here is a schematic for a typical module
 DS3231 schematic
Connection
| Arduino Pins |
Module Pins |
| GND |
GND |
| 5v |
VCC |
| A4 |
SDA |
| A5 |
SCL |
Code
This uses the RTCLib – https://github.com/adafruit/RTClib
#include <Wire.h>
#include "RTClib.h"
RTC_DS3231 rtc;
char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
void setup () {
#ifndef ESP8266
while (!Serial); // for Leonardo/Micro/Zero
#endif
Serial.begin(9600);
delay(3000); // wait for console opening
if (! rtc.begin()) {
Serial.println("Couldn't find RTC");
while (1);
}
if (rtc.lostPower()) {
Serial.println("RTC lost power, lets set the time!");
// following line sets the RTC to the date & time this sketch was compiled
rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
// This line sets the RTC with an explicit date & time, for example to set
// January 21, 2014 at 3am you would call:
// rtc.adjust(DateTime(2014, 1, 21, 3, 0, 0));
}
}
void loop () {
DateTime now = rtc.now();
Serial.print(now.year(), DEC);
Serial.print('/');
Serial.print(now.month(), DEC);
Serial.print('/');
Serial.print(now.day(), DEC);
Serial.print(" (");
Serial.print(daysOfTheWeek[now.dayOfTheWeek()]);
Serial.print(") ");
Serial.print(now.hour(), DEC);
Serial.print(':');
Serial.print(now.minute(), DEC);
Serial.print(':');
Serial.print(now.second(), DEC);
Serial.println();
Serial.print(" since midnight 1/1/1970 = ");
Serial.print(now.unixtime());
Serial.print("s = ");
Serial.print(now.unixtime() / 86400L);
Serial.println("d");
// calculate a date which is 7 days and 30 seconds into the future
DateTime future (now + TimeSpan(7,12,30,6));
Serial.print(" now + 7d + 30s: ");
Serial.print(future.year(), DEC);
Serial.print('/');
Serial.print(future.month(), DEC);
Serial.print('/');
Serial.print(future.day(), DEC);
Serial.print(' ');
Serial.print(future.hour(), DEC);
Serial.print(':');
Serial.print(future.minute(), DEC);
Serial.print(':');
Serial.print(future.second(), DEC);
Serial.println();
Serial.println();
delay(3000);
}
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