Overview
In this blog post, we will make Mini Weather Station using DHT11/DHT22 Humidity Temperature Sensor & Raspberry Pi Pico. A weather station automatically measure, record, and sometimes transmit weather data.
In this project, the ambient temperature value and humidity value are monitored in real-time through the DHT11/DHT22 Temperature & Humidity sensor and is shown on the 16×2 I2C LCD module.
Parts Required
Following are the parts required
- Raspberry Pi Pico Board – 1
- 16×2 I2C LCD Display – 1
- DHT11 Humidity Temperature Sensor – 1
- Breadboard – 1
- Jumper Wires – 4
- Micro-USB Cable – 1
DHT11 Temperature and Humidity sensor overview
The DHT11/DHT22 is a commonly used Temperature and humidity sensor that comes with a dedicated NTC to measure temperature and an 8-bit microcontroller to output the values of temperature and humidity as serial data. The sensor is also factory calibrated and hence easy to interface with other microcontrollers.
Circuit Diagram and connections [ Schematic Diagram]
Wiring
PICO 5v ——————- LCD VCC
PICO GND —————- LCD GND
PICO GP0 —————– LCD SDA
PICO GP1 —————– LCD SCL
PICO VSYS —————- DHT11 VDD
PICO GND —————- DHT11 GND
PICO GP2 —————– DHT11 Output/Data
Code/Program
Code is divided in 4 parts.
pico_i2c_LCD.py
lcd_api.py – This will go into Raspberry pi PICO. This is an API to make LCD run using PICO
dht.py
main.py
LCD and DHT11 sensor require libraries to run and are pre-requisite.
lcd_api.py
"""Provides an API for talking to HD44780 compatible character LCDs."""
import time
class LcdApi:
"""Implements the API for talking with HD44780 compatible character LCDs.
This class only knows what commands to send to the LCD, and not how to get
them to the LCD.
It is expected that a derived class will implement the hal_xxx functions.
"""
# The following constant names were lifted from the avrlib lcd.h
# header file, however, I changed the definitions from bit numbers
# to bit masks.
#
# HD44780 LCD controller command set
LCD_CLR = 0x01 # DB0: clear display
LCD_HOME = 0x02 # DB1: return to home position
LCD_ENTRY_MODE = 0x04 # DB2: set entry mode
LCD_ENTRY_INC = 0x02 # --DB1: increment
LCD_ENTRY_SHIFT = 0x01 # --DB0: shift
LCD_ON_CTRL = 0x08 # DB3: turn lcd/cursor on
LCD_ON_DISPLAY = 0x04 # --DB2: turn display on
LCD_ON_CURSOR = 0x02 # --DB1: turn cursor on
LCD_ON_BLINK = 0x01 # --DB0: blinking cursor
LCD_MOVE = 0x10 # DB4: move cursor/display
LCD_MOVE_DISP = 0x08 # --DB3: move display (0-> move cursor)
LCD_MOVE_RIGHT = 0x04 # --DB2: move right (0-> left)
LCD_FUNCTION = 0x20 # DB5: function set
LCD_FUNCTION_8BIT = 0x10 # --DB4: set 8BIT mode (0->4BIT mode)
LCD_FUNCTION_2LINES = 0x08 # --DB3: two lines (0->one line)
LCD_FUNCTION_10DOTS = 0x04 # --DB2: 5x10 font (0->5x7 font)
LCD_FUNCTION_RESET = 0x30 # See "Initializing by Instruction" section
LCD_CGRAM = 0x40 # DB6: set CG RAM address
LCD_DDRAM = 0x80 # DB7: set DD RAM address
LCD_RS_CMD = 0
LCD_RS_DATA = 1
LCD_RW_WRITE = 0
LCD_RW_READ = 1
def __init__(self, num_lines, num_columns):
self.num_lines = num_lines
if self.num_lines > 4:
self.num_lines = 4
self.num_columns = num_columns
if self.num_columns > 40:
self.num_columns = 40
self.cursor_x = 0
self.cursor_y = 0
self.backlight = True
self.display_off()
self.backlight_on()
self.clear()
self.hal_write_command(self.LCD_ENTRY_MODE | self.LCD_ENTRY_INC)
self.hide_cursor()
self.display_on()
def clear(self):
"""Clears the LCD display and moves the cursor to the top left
corner.
"""
self.hal_write_command(self.LCD_CLR)
self.hal_write_command(self.LCD_HOME)
self.cursor_x = 0
self.cursor_y = 0
def show_cursor(self):
"""Causes the cursor to be made visible."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
self.LCD_ON_CURSOR)
def hide_cursor(self):
"""Causes the cursor to be hidden."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY)
def blink_cursor_on(self):
"""Turns on the cursor, and makes it blink."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
self.LCD_ON_CURSOR | self.LCD_ON_BLINK)
def blink_cursor_off(self):
"""Turns on the cursor, and makes it no blink (i.e. be solid)."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY |
self.LCD_ON_CURSOR)
def display_on(self):
"""Turns on (i.e. unblanks) the LCD."""
self.hal_write_command(self.LCD_ON_CTRL | self.LCD_ON_DISPLAY)
def display_off(self):
"""Turns off (i.e. blanks) the LCD."""
self.hal_write_command(self.LCD_ON_CTRL)
def backlight_on(self):
"""Turns the backlight on.
This isn't really an LCD command, but some modules have backlight
controls, so this allows the hal to pass through the command.
"""
self.backlight = True
self.hal_backlight_on()
def backlight_off(self):
"""Turns the backlight off.
This isn't really an LCD command, but some modules have backlight
controls, so this allows the hal to pass through the command.
"""
self.backlight = False
self.hal_backlight_off()
def move_to(self, cursor_x, cursor_y):
"""Moves the cursor position to the indicated position. The cursor
position is zero based (i.e. cursor_x == 0 indicates first column).
"""
self.cursor_x = cursor_x
self.cursor_y = cursor_y
addr = cursor_x & 0x3f
if cursor_y & 1:
addr += 0x40 # Lines 1 & 3 add 0x40
if cursor_y & 2:
addr += 0x14 # Lines 2 & 3 add 0x14
self.hal_write_command(self.LCD_DDRAM | addr)
def putchar(self, char):
"""Writes the indicated character to the LCD at the current cursor
position, and advances the cursor by one position.
"""
if char != '\n':
self.hal_write_data(ord(char))
self.cursor_x += 1
if self.cursor_x >= self.num_columns or char == '\n':
self.cursor_x = 0
self.cursor_y += 1
if self.cursor_y >= self.num_lines:
self.cursor_y = 0
self.move_to(self.cursor_x, self.cursor_y)
def putstr(self, string):
"""Write the indicated string to the LCD at the current cursor
position and advances the cursor position appropriately.
"""
for char in string:
self.putchar(char)
def custom_char(self, location, charmap):
"""Write a character to one of the 8 CGRAM locations, available
as chr(0) through chr(7).
"""
location &= 0x7
self.hal_write_command(self.LCD_CGRAM | (location << 3))
time.sleep_us(40)
for i in range(8):
self.hal_write_data(charmap[i])
time.sleep_us(40)
self.move_to(self.cursor_x, self.cursor_y)
def hal_backlight_on(self):
"""Allows the hal layer to turn the backlight on.
If desired, a derived HAL class will implement this function.
"""
pass
def hal_backlight_off(self):
"""Allows the hal layer to turn the backlight off.
If desired, a derived HAL class will implement this function.
"""
pass
def hal_write_command(self, cmd):
"""Write a command to the LCD.
It is expected that a derived HAL class will implement this
function.
"""
raise NotImplementedError
def hal_write_data(self, data):
"""Write data to the LCD.
It is expected that a derived HAL class will implement this
function.
"""
raise NotImplementedErrorpico_i2c_LCD.py
from lcd_api import LcdApi
from machine import I2C
from time import sleep_ms
# The PCF8574 has a jumper selectable address: 0x20 - 0x27
DEFAULT_I2C_ADDR = 0x27
# Defines shifts or masks for the various LCD line attached to the PCF8574
MASK_RS = 0x01
MASK_RW = 0x02
MASK_E = 0x04
SHIFT_BACKLIGHT = 3
SHIFT_DATA = 4
class I2cLcd(LcdApi):
"""Implements a HD44780 character LCD connected via PCF8574 on I2C."""
def __init__(self, i2c, i2c_addr, num_lines, num_columns):
self.i2c = i2c
self.i2c_addr = i2c_addr
self.i2c.writeto(self.i2c_addr, bytearray([0]))
sleep_ms(20) # Allow LCD time to powerup
# Send reset 3 times
self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
sleep_ms(5) # need to delay at least 4.1 msec
self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
sleep_ms(1)
self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
sleep_ms(1)
# Put LCD into 4 bit mode
self.hal_write_init_nibble(self.LCD_FUNCTION)
sleep_ms(1)
LcdApi.__init__(self, num_lines, num_columns)
cmd = self.LCD_FUNCTION
if num_lines > 1:
cmd |= self.LCD_FUNCTION_2LINES
self.hal_write_command(cmd)
def hal_write_init_nibble(self, nibble):
"""Writes an initialization nibble to the LCD.
This particular function is only used during initialization.
"""
byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
self.i2c.writeto(self.i2c_addr, bytearray([byte]))
def hal_backlight_on(self):
"""Allows the hal layer to turn the backlight on."""
self.i2c.writeto(self.i2c_addr, bytearray([1 << SHIFT_BACKLIGHT]))
def hal_backlight_off(self):
"""Allows the hal layer to turn the backlight off."""
self.i2c.writeto(self.i2c_addr, bytearray([0]))
def hal_write_command(self, cmd):
"""Writes a command to the LCD.
Data is latched on the falling edge of E.
"""
byte = ((self.backlight << SHIFT_BACKLIGHT) | (((cmd >> 4) & 0x0f) << SHIFT_DATA))
self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
self.i2c.writeto(self.i2c_addr, bytearray([byte]))
byte = ((self.backlight << SHIFT_BACKLIGHT) | ((cmd & 0x0f) << SHIFT_DATA))
self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
self.i2c.writeto(self.i2c_addr, bytearray([byte]))
if cmd <= 3:
# The home and clear commands require a worst case delay of 4.1 msec
sleep_ms(5)
def hal_write_data(self, data):
"""Write data to the LCD."""
byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | (((data >> 4) & 0x0f) << SHIFT_DATA))
self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
self.i2c.writeto(self.i2c_addr, bytearray([byte]))
byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | ((data & 0x0f) << SHIFT_DATA))
self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
self.i2c.writeto(self.i2c_addr, bytearray([byte]))DHT.py
import array
import micropython
import utime
from machine import Pin
from micropython import const
class InvalidChecksum(Exception):
pass
class InvalidPulseCount(Exception):
pass
MAX_UNCHANGED = const(100)
MIN_INTERVAL_US = const(200000)
HIGH_LEVEL = const(50)
EXPECTED_PULSES = const(84)
class DHT11:
_temperature: int
_humidity: int
def __init__(self, pin):
self._pin = pin
self._last_measure = utime.ticks_us()
self._temperature = -1
self._humidity = -1
def measure(self):
current_ticks = utime.ticks_us()
if utime.ticks_diff(current_ticks, self._last_measure) < MIN_INTERVAL_US and (
self._temperature > -1 or self._humidity > -1
):
# Less than a second since last read, which is too soon according
# to the datasheet
return
self._send_init_signal()
pulses = self._capture_pulses()
buffer = self._convert_pulses_to_buffer(pulses)
self._verify_checksum(buffer)
self._humidity = buffer[0] + buffer[1] / 10
self._temperature = buffer[2] + buffer[3] / 10
self._last_measure = utime.ticks_us()
@property
def humidity(self):
self.measure()
return self._humidity
@property
def temperature(self):
self.measure()
return self._temperature
def _send_init_signal(self):
self._pin.init(Pin.OUT, Pin.PULL_DOWN)
self._pin.value(1)
utime.sleep_ms(50)
self._pin.value(0)
utime.sleep_ms(18)
@micropython.native
def _capture_pulses(self):
pin = self._pin
pin.init(Pin.IN, Pin.PULL_UP)
val = 1
idx = 0
transitions = bytearray(EXPECTED_PULSES)
unchanged = 0
timestamp = utime.ticks_us()
while unchanged < MAX_UNCHANGED:
if val != pin.value():
if idx >= EXPECTED_PULSES:
raise InvalidPulseCount(
"Got more than {} pulses".format(EXPECTED_PULSES)
)
now = utime.ticks_us()
transitions[idx] = now - timestamp
timestamp = now
idx += 1
val = 1 - val
unchanged = 0
else:
unchanged += 1
pin.init(Pin.OUT, Pin.PULL_DOWN)
if idx != EXPECTED_PULSES:
raise InvalidPulseCount(
"Expected {} but got {} pulses".format(EXPECTED_PULSES, idx)
)
return transitions[4:]
def _convert_pulses_to_buffer(self, pulses):
"""Convert a list of 80 pulses into a 5 byte buffer
The resulting 5 bytes in the buffer will be:
0: Integral relative humidity data
1: Decimal relative humidity data
2: Integral temperature data
3: Decimal temperature data
4: Checksum
"""
# Convert the pulses to 40 bits
binary = 0
for idx in range(0, len(pulses), 2):
binary = binary << 1 | int(pulses[idx] > HIGH_LEVEL)
# Split into 5 bytes
buffer = array.array("B")
for shift in range(4, -1, -1):
buffer.append(binary >> shift * 8 & 0xFF)
return buffer
def _verify_checksum(self, buffer):
# Calculate checksum
checksum = 0
for buf in buffer[0:4]:
checksum += buf
if checksum & 0xFF != buffer[4]:
raise InvalidChecksum()main.py
from machine import I2C, Pin
from i2c_lcd import I2cLcd
from utime import sleep
from dht import DHT11, InvalidChecksum
DEFAULT_I2C_ADDR = 0x27 # LCD 1602 I2C address
pin = Pin(2, Pin.OUT, Pin.PULL_DOWN)
dht11 = DHT11(pin)
def setup():
global lcd
i2c = I2C(0,sda=Pin(0),scl=Pin(1),freq=400000)
lcd = I2cLcd(i2c, DEFAULT_I2C_ADDR, 2, 16) # Initialize(device address, cursor settings)
def loop():
try:
while True:
lcd.move_to(0,0)
lcd.putstr("Temp: {}".format(dht11.temperature))
lcd.move_to(0,1)
lcd.putstr("Humi: {}".format(dht11.humidity))
sleep(1)
lcd.clear()
except InvalidChecksum:
print("Checksum from the sensor was invalid")
if __name__ == '__main__':
setup()
loop()Copy all the files to PICO and then run. For more information on how to setup and run programs in Raspberry Pi PICO follow my post on getting started with Raspberry pi PICO.
Note: You can also copy the LCD API from GitHub location https://github.com/T-622/RPI-PICO-I2C-LCD
Note: You can ignore dht.py and instead import dht package in Thorny and use the library directly.
