In this project, we will be creating a Raspberry Pi Pico data logger using an SD card and DHT11 sensor. This data logger will be able to log data to an SD card and also measure temperature and humidity using the DHT11 sensor. The DHT11 is a low-cost temperature and humidity sensor that is usually used in weather stations. The data logger will record the temperature and humidity every minute and save it to a file on the SD card.
A data logger keeps track of the temperature and humidity (moisture) levels in your surroundings. It can record environmental data over time, helping you monitor your surroundings. Raspberry Pi Pico Weather Station Using DHT11 Sensor
Our data logger will record temperature and humidity values every second and save them in a convenient. .TXT file on the SD card.
Required Material
- Raspberry Pi Pico
- DHT11 temperature and humidity sensor
- SD Card Module
- MicroSD card
- Breadboard
- Jumper wires
SD Card Module
The SD Card Module is a small electronic device that allows Raspberry Pi Pico to store and recover data on SD memory cards. It has a slot for the memory card and some pins to communicate with the microcontroller. You can use it for data storage, logging, and other applications.
The SD Card Module needs 5V power from the Pico board. It has a voltage regulator (AMS1117) that converts the 5V to a stable 3.3V for the SD card. There’s also a voltage level converter (74LVC125A) that changes the 5V signals to 3.3V so that the SD card and module can communicate more smoothly. This way, it works with both 5V microcontrollers like Arduino and 3.3V SD cards. read my previous post on Interfacing Micro SD Card Module with Raspberry Pi Pico
Pinout of SD Card Module
- GND: Ground.
- VCC: +5V power supply.
- MISO: SPI output
- MOSI: SPI input
- SCK: Serial Clock for data synchronization.
- CS: Chip Select (enables/disables the module).
Preparing the SD card
- Insert the SD card into your computer.
- Right-click on the SD card in My Computer.
- Choose “Format” and select FAT32 as the file system.
- Click “Start” to start the formatting process.
- Once the formatting is complete, your SD card is ready for use with the SD Card Module in your project applications.
Wiring Raspberry Pi Pico Data Logger Using SD card and DHT11 sensor
Connect the SD Card Module to Raspberry Pi Pico as per the below Circuit Diagram.
DHT11 Sensor:
- VCC to 3V3 (3.3V) pin
- GND to any GND pin
- OUT to GPIO pin 5 (GP5)
SD Card:
- Insert a Micro SD card into the adapter
- GND to any GND pin
- VCC to 3V3 (3.3V) pin
- MISO to GPIO pin 4 (GP4)
- MOSI to GPIO pin 3 (GP3)
- SCK to GPIO pin 2 (GP2)
- CS to GPIO pin 1 (GP1)
Double-check your connections before powering up your Raspberry Pi Pico.
Micropython code & libraries
You’ll need two libraries to work with the SD card and DHT11 sensor. Ensure you have the sdcard library and the dhtthe library if you haven’t copy below code and save it to Raspberry Pi Pico.
- sdcard.py
- dht.py
- main.py
sdcard.py
Open your Thonny IDE and paste the following code. Save the file on the Raspberry Pi Pico and name the file sdcard.py.
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""" MicroPython driver for SD cards using SPI bus. Origial: https://github.com/micropython/micropython/tree/master/drivers/sdcard RAW: https://raw.githubusercontent.com/micropython/micropython/master/drivers/sdcard/sdcard.py Requires an SPI bus and a CS pin. Provides readblocks and writeblocks methods so the device can be mounted as a filesystem. Example usage on pyboard: import pyb, sdcard, os sd = sdcard.SDCard(pyb.SPI(1), pyb.Pin.board.X5) pyb.mount(sd, '/sd2') os.listdir('/') Example usage on ESP8266: import machine, sdcard, os sd = sdcard.SDCard(machine.SPI(1), machine.Pin(15)) os.mount(sd, '/sd') os.listdir('/') """ from micropython import const import time _CMD_TIMEOUT = const(100) _R1_IDLE_STATE = const(1 << 0) # R1_ERASE_RESET = const(1 << 1) _R1_ILLEGAL_COMMAND = const(1 << 2) # R1_COM_CRC_ERROR = const(1 << 3) # R1_ERASE_SEQUENCE_ERROR = const(1 << 4) # R1_ADDRESS_ERROR = const(1 << 5) # R1_PARAMETER_ERROR = const(1 << 6) _TOKEN_CMD25 = const(0xFC) _TOKEN_STOP_TRAN = const(0xFD) _TOKEN_DATA = const(0xFE) class SDCard: def __init__(self, spi, cs, baudrate=1320000): self.spi = spi self.cs = cs self.cmdbuf = bytearray(6) self.dummybuf = bytearray(512) self.tokenbuf = bytearray(1) for i in range(512): self.dummybuf[i] = 0xFF self.dummybuf_memoryview = memoryview(self.dummybuf) # initialise the card self.init_card(baudrate) def init_spi(self, baudrate): try: master = self.spi.MASTER except AttributeError: # on ESP8266 self.spi.init(baudrate=baudrate, phase=0, polarity=0) else: # on pyboard self.spi.init(master, baudrate=baudrate, phase=0, polarity=0) def init_card(self, baudrate): # init CS pin self.cs.init(self.cs.OUT, value=1) # init SPI bus; use low data rate for initialisation self.init_spi(100000) # clock card at least 100 cycles with cs high for i in range(16): self.spi.write(b"\xff") # CMD0: init card; should return _R1_IDLE_STATE (allow 5 attempts) for _ in range(5): if self.cmd(0, 0, 0x95) == _R1_IDLE_STATE: break else: raise OSError("no SD card") # CMD8: determine card version r = self.cmd(8, 0x01AA, 0x87, 4) if r == _R1_IDLE_STATE: self.init_card_v2() elif r == (_R1_IDLE_STATE | _R1_ILLEGAL_COMMAND): self.init_card_v1() else: raise OSError("couldn't determine SD card version") # get the number of sectors # CMD9: response R2 (R1 byte + 16-byte block read) if self.cmd(9, 0, 0, 0, False) != 0: raise OSError("no response from SD card") csd = bytearray(16) self.readinto(csd) if csd[0] & 0xC0 == 0x40: # CSD version 2.0 self.sectors = ((csd[8] << 8 | csd[9]) + 1) * 1024 elif csd[0] & 0xC0 == 0x00: # CSD version 1.0 (old, <=2GB) c_size = (csd[6] & 0b11) << 10 | csd[7] << 2 | csd[8] >> 6 c_size_mult = (csd[9] & 0b11) << 1 | csd[10] >> 7 read_bl_len = csd[5] & 0b1111 capacity = (c_size + 1) * (2 ** (c_size_mult + 2)) * (2**read_bl_len) self.sectors = capacity // 512 else: raise OSError("SD card CSD format not supported") # print('sectors', self.sectors) # CMD16: set block length to 512 bytes if self.cmd(16, 512, 0) != 0: raise OSError("can't set 512 block size") # set to high data rate now that it's initialised self.init_spi(baudrate) def init_card_v1(self): for i in range(_CMD_TIMEOUT): self.cmd(55, 0, 0) if self.cmd(41, 0, 0) == 0: # SDSC card, uses byte addressing in read/write/erase commands self.cdv = 512 # print("[SDCard] v1 card") return raise OSError("timeout waiting for v1 card") def init_card_v2(self): for i in range(_CMD_TIMEOUT): time.sleep_ms(50) self.cmd(58, 0, 0, 4) self.cmd(55, 0, 0) if self.cmd(41, 0x40000000, 0) == 0: self.cmd(58, 0, 0, -4) # 4-byte response, negative means keep the first byte ocr = self.tokenbuf[0] # get first byte of response, which is OCR if not ocr & 0x40: # SDSC card, uses byte addressing in read/write/erase commands self.cdv = 512 else: # SDHC/SDXC card, uses block addressing in read/write/erase commands self.cdv = 1 # print("[SDCard] v2 card") return raise OSError("timeout waiting for v2 card") def cmd(self, cmd, arg, crc, final=0, release=True, skip1=False): self.cs(0) # create and send the command buf = self.cmdbuf buf[0] = 0x40 | cmd buf[1] = arg >> 24 buf[2] = arg >> 16 buf[3] = arg >> 8 buf[4] = arg buf[5] = crc self.spi.write(buf) if skip1: self.spi.readinto(self.tokenbuf, 0xFF) # wait for the response (response[7] == 0) for i in range(_CMD_TIMEOUT): self.spi.readinto(self.tokenbuf, 0xFF) response = self.tokenbuf[0] if not (response & 0x80): # this could be a big-endian integer that we are getting here # if final<0 then store the first byte to tokenbuf and discard the rest if final < 0: self.spi.readinto(self.tokenbuf, 0xFF) final = -1 - final for j in range(final): self.spi.write(b"\xff") if release: self.cs(1) self.spi.write(b"\xff") return response # timeout self.cs(1) self.spi.write(b"\xff") return -1 def readinto(self, buf): self.cs(0) # read until start byte (0xff) for i in range(_CMD_TIMEOUT): self.spi.readinto(self.tokenbuf, 0xFF) if self.tokenbuf[0] == _TOKEN_DATA: break time.sleep_ms(1) else: self.cs(1) raise OSError("timeout waiting for response") # read data mv = self.dummybuf_memoryview if len(buf) != len(mv): mv = mv[: len(buf)] self.spi.write_readinto(mv, buf) # read checksum self.spi.write(b"\xff") self.spi.write(b"\xff") self.cs(1) self.spi.write(b"\xff") def write(self, token, buf): self.cs(0) # send: start of block, data, checksum self.spi.read(1, token) self.spi.write(buf) self.spi.write(b"\xff") self.spi.write(b"\xff") # check the response if (self.spi.read(1, 0xFF)[0] & 0x1F) != 0x05: self.cs(1) self.spi.write(b"\xff") return # wait for write to finish while self.spi.read(1, 0xFF)[0] == 0: pass self.cs(1) self.spi.write(b"\xff") def write_token(self, token): self.cs(0) self.spi.read(1, token) self.spi.write(b"\xff") # wait for write to finish while self.spi.read(1, 0xFF)[0] == 0x00: pass self.cs(1) self.spi.write(b"\xff") def readblocks(self, block_num, buf): nblocks = len(buf) // 512 assert nblocks and not len(buf) % 512, "Buffer length is invalid" if nblocks == 1: # CMD17: set read address for single block if self.cmd(17, block_num * self.cdv, 0, release=False) != 0: # release the card self.cs(1) raise OSError(5) # EIO # receive the data and release card self.readinto(buf) else: # CMD18: set read address for multiple blocks if self.cmd(18, block_num * self.cdv, 0, release=False) != 0: # release the card self.cs(1) raise OSError(5) # EIO offset = 0 mv = memoryview(buf) while nblocks: # receive the data and release card self.readinto(mv[offset : offset + 512]) offset += 512 nblocks -= 1 if self.cmd(12, 0, 0xFF, skip1=True): raise OSError(5) # EIO def writeblocks(self, block_num, buf): nblocks, err = divmod(len(buf), 512) assert nblocks and not err, "Buffer length is invalid" if nblocks == 1: # CMD24: set write address for single block if self.cmd(24, block_num * self.cdv, 0) != 0: raise OSError(5) # EIO # send the data self.write(_TOKEN_DATA, buf) else: # CMD25: set write address for first block if self.cmd(25, block_num * self.cdv, 0) != 0: raise OSError(5) # EIO # send the data offset = 0 mv = memoryview(buf) while nblocks: self.write(_TOKEN_CMD25, mv[offset : offset + 512]) offset += 512 nblocks -= 1 self.write_token(_TOKEN_STOP_TRAN) def ioctl(self, op, arg): if op == 4: # get number of blocks return self.sectors if op == 5: # get block size in bytes return 512 |
dht.py
open another tab on the same window paste the code mentioned below and save the file as dht.py in Raspberry Pi Pico.
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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
Open another last tab on the window paste the code mentioned below and save the file as main.py in Raspberry Pi Pico.
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import machine import sdcard import uos import dht import utime # DHT11 data pin dht_sensor = dht.DHT11(machine.Pin(5)) # Assign chip select (CS) pin (and start it high) cs = machine.Pin(1, machine.Pin.OUT) # Initialize SPI peripheral (start with 1 MHz) spi = machine.SPI(0, baudrate=1000000, polarity=0, phase=0, bits=8, firstbit=machine.SPI.MSB, sck=machine.Pin(2), mosi=machine.Pin(3), miso=machine.Pin(4)) # Initialize SD card sd = sdcard.SDCard(spi, cs) # Mount filesystem vfs = uos.VfsFat(sd) uos.mount(vfs, "/sd") # Run this in an infinite loop to continuously log sensor data while True: try: dht_sensor.measure() temp = dht_sensor.temperature # No parentheses here humidity = dht_sensor.humidity # No parentheses here # Create a file and write the sensor readings to it with open("/sd/sensor_log.txt", "a") as file: file.write("Temperature: {}C, Humidity: {}%\r\n".format(temp, humidity)) # Open the file we just created and read from it with open("/sd/sensor_log.txt", "r") as file: data = file.read() print(data) except Exception as e: print('Failed to read sensor.', e) # Sleep for 1 minute before next reading utime.sleep(5) |
Run the main.py file now. If the hardware connection is correct, the Shell will report the following information.
You can check the value of temperature and humidity in thonny shell.
Firstly, I powered my circuit and after a few seconds I turned it OFF, I removed my SD card from the circuit and placed it in my computer, I opened my SD card with Windows and I got the file shown below:
The data is separated by commas, and each reading is in a new line. In this format, you can easily import data to Excel or other data processing software.
