Quick reference for the ESP32¶
The Espressif ESP32 Development Board (image attribution: Adafruit).
Below is a quick reference for ESP32-based boards. If it is your first time working with this board it may be useful to get an overview of the microcontroller:
See the corresponding section of tutorial: Getting started with MicroPython on the ESP32. It also includes a troubleshooting subsection.
General board control¶
The MicroPython REPL is on UART0 (GPIO1=TX, GPIO3=RX) at baudrate 115200. Tab-completion is useful to find out what methods an object has. Paste mode (ctrl-E) is useful to paste a large slab of Python code into the REPL.
import machine machine.freq() # get the current frequency of the CPU machine.freq(240000000) # set the CPU frequency to 240 MHz
import esp esp.osdebug(None) # turn off vendor O/S debugging messages esp.osdebug(0) # redirect vendor O/S debugging messages to UART(0) # low level methods to interact with flash storage esp.flash_size() esp.flash_user_start() esp.flash_erase(sector_no) esp.flash_write(byte_offset, buffer) esp.flash_read(byte_offset, buffer)
import esp32 esp32.hall_sensor() # read the internal hall sensor esp32.raw_temperature() # read the internal temperature of the MCU, in Farenheit esp32.ULP() # access to the Ultra-Low-Power Co-processor
Note that the temperature sensor in the ESP32 will typically read higher than ambient due to the IC getting warm while it runs. This effect can be minimised by reading the temperature sensor immediately after waking up from sleep.
import network wlan = network.WLAN(network.STA_IF) # create station interface wlan.active(True) # activate the interface wlan.scan() # scan for access points wlan.isconnected() # check if the station is connected to an AP wlan.connect('essid', 'password') # connect to an AP wlan.config('mac') # get the interface's MAC adddress wlan.ifconfig() # get the interface's IP/netmask/gw/DNS addresses ap = network.WLAN(network.AP_IF) # create access-point interface ap.config(essid='ESP-AP') # set the ESSID of the access point ap.active(True) # activate the interface
A useful function for connecting to your local WiFi network is:
def do_connect(): import network wlan = network.WLAN(network.STA_IF) wlan.active(True) if not wlan.isconnected(): print('connecting to network...') wlan.connect('essid', 'password') while not wlan.isconnected(): pass print('network config:', wlan.ifconfig())
Once the network is established the
socket module can be used
to create and use TCP/UDP sockets as usual, and the
urequests module for
convenient HTTP requests.
Delay and timing¶
import time time.sleep(1) # sleep for 1 second time.sleep_ms(500) # sleep for 500 milliseconds time.sleep_us(10) # sleep for 10 microseconds start = time.ticks_ms() # get millisecond counter delta = time.ticks_diff(time.ticks_ms(), start) # compute time difference
Virtual (RTOS-based) timers are supported. Use the machine.Timer class with timer ID of -1:
from machine import Timer tim = Timer(-1) tim.init(period=5000, mode=Timer.ONE_SHOT, callback=lambda t:print(1)) tim.init(period=2000, mode=Timer.PERIODIC, callback=lambda t:print(2))
The period is in milliseconds.
Pins and GPIO¶
Use the machine.Pin class:
from machine import Pin p0 = Pin(0, Pin.OUT) # create output pin on GPIO0 p0.on() # set pin to "on" (high) level p0.off() # set pin to "off" (low) level p0.value(1) # set pin to on/high p2 = Pin(2, Pin.IN) # create input pin on GPIO2 print(p2.value()) # get value, 0 or 1 p4 = Pin(4, Pin.IN, Pin.PULL_UP) # enable internal pull-up resistor p5 = Pin(5, Pin.OUT, value=1) # set pin high on creation
Available Pins are from the following ranges (inclusive): 0-19, 21-23, 25-27, 32-39. These correspond to the actual GPIO pin numbers of ESP32 chip. Note that many end-user boards use their own adhoc pin numbering (marked e.g. D0, D1, …). For mapping between board logical pins and physical chip pins consult your board documentation.
- Pins 1 and 3 are REPL UART TX and RX respectively
- Pins 6, 7, 8, 11, 16, and 17 are used for connecting the embedded flash, and are not recommended for other uses
- Pins 34-39 are input only, and also do not have internal pull-up resistors
- The pull value of some pins can be set to
Pin.PULL_HOLDto reduce power consumption during deepsleep.
PWM (pulse width modulation)¶
PWM can be enabled on all output-enabled pins. The base frequency can range from 1Hz to 40MHz but there is a tradeoff; as the base frequency increases the duty resolution decreases. See LED Control for more details.
from machine import Pin, PWM pwm0 = PWM(Pin(0)) # create PWM object from a pin pwm0.freq() # get current frequency pwm0.freq(1000) # set frequency pwm0.duty() # get current duty cycle pwm0.duty(200) # set duty cycle pwm0.deinit() # turn off PWM on the pin pwm2 = PWM(Pin(2), freq=20000, duty=512) # create and configure in one go
ADC (analog to digital conversion)¶
On the ESP32 ADC functionality is available on Pins 32-39. Note that, when using the default configuration, input voltages on the ADC pin must be between 0.0v and 1.0v (anything above 1.0v will just read as 4095). Attenuation must be applied in order to increase this usable voltage range.
Use the machine.ADC class:
from machine import ADC adc = ADC(Pin(32)) # create ADC object on ADC pin adc.read() # read value, 0-4095 across voltage range 0.0v - 1.0v adc.atten(ADC.ATTN_11DB) # set 11dB input attentuation (voltage range roughly 0.0v - 3.6v) adc.width(ADC.WIDTH_9BIT) # set 9 bit return values (returned range 0-511) adc.read() # read value using the newly configured attenuation and width
ESP32 specific ADC class method reference:
This method allows for the setting of the amount of attenuation on the input of the ADC. This allows for a wider possible input voltage range, at the cost of accuracy (the same number of bits now represents a wider range). The possible attenuation options are:
ADC.ATTN_0DB: 0dB attenuation, gives a maximum input voltage of 1.00v - this is the default configuration
ADC.ATTN_2_5DB: 2.5dB attenuation, gives a maximum input voltage of approximately 1.34v
ADC.ATTN_6DB: 6dB attenuation, gives a maximum input voltage of approximately 2.00v
ADC.ATTN_11DB: 11dB attenuation, gives a maximum input voltage of approximately 3.6v
Despite 11dB attenuation allowing for up to a 3.6v range, note that the absolute maximum voltage rating for the input pins is 3.6v, and so going near this boundary may be damaging to the IC!
This method allows for the setting of the number of bits to be utilised and returned during ADC reads. Possible width options are:
ADC.WIDTH_9BIT: 9 bit data
ADC.WIDTH_10BIT: 10 bit data
ADC.WIDTH_11BIT: 11 bit data
ADC.WIDTH_12BIT: 12 bit data - this is the default configuration
Software SPI bus¶
There are two SPI drivers. One is implemented in software (bit-banging) and works on all pins, and is accessed via the machine.SPI class:
from machine import Pin, SPI # construct an SPI bus on the given pins # polarity is the idle state of SCK # phase=0 means sample on the first edge of SCK, phase=1 means the second spi = SPI(baudrate=100000, polarity=1, phase=0, sck=Pin(0), mosi=Pin(2), miso=Pin(4)) spi.init(baudrate=200000) # set the baudrate spi.read(10) # read 10 bytes on MISO spi.read(10, 0xff) # read 10 bytes while outputing 0xff on MOSI buf = bytearray(50) # create a buffer spi.readinto(buf) # read into the given buffer (reads 50 bytes in this case) spi.readinto(buf, 0xff) # read into the given buffer and output 0xff on MOSI spi.write(b'12345') # write 5 bytes on MOSI buf = bytearray(4) # create a buffer spi.write_readinto(b'1234', buf) # write to MOSI and read from MISO into the buffer spi.write_readinto(buf, buf) # write buf to MOSI and read MISO back into buf
Currently all of
miso must be specified when
initialising Software SPI.
Hardware SPI bus¶
There are two hardware SPI channels that allow faster transmission rates (up to 80Mhz). These may be used on any IO pins that support the required direction and are otherwise unused (see Pins and GPIO) but if they are not configured to their default pins then they need to pass through an extra layer of GPIO multiplexing, which can impact their reliability at high speeds. Hardware SPI channels are limited to 40MHz when used on pins other than the default ones listed below.
|HSPI (id=1)||VSPI (id=2)|
Hardware SPI has the same methods as Software SPI above:
from machine import Pin, SPI hspi = SPI(1, 10000000, sck=Pin(14), mosi=Pin(13), miso=Pin(12)) vspi = SPI(2, baudrate=80000000, polarity=0, phase=0, bits=8, firstbit=0, sck=Pin(18), mosi=Pin(23), miso=Pin(19))
The I2C driver is implemented in software and works on all pins, and is accessed via the machine.I2C class:
from machine import Pin, I2C # construct an I2C bus i2c = I2C(scl=Pin(5), sda=Pin(4), freq=100000) i2c.readfrom(0x3a, 4) # read 4 bytes from slave device with address 0x3a i2c.writeto(0x3a, '12') # write '12' to slave device with address 0x3a buf = bytearray(10) # create a buffer with 10 bytes i2c.writeto(0x3a, buf) # write the given buffer to the slave
Real time clock (RTC)¶
from machine import RTC rtc = RTC() rtc.datetime((2017, 8, 23, 1, 12, 48, 0, 0)) # set a specific date and time rtc.datetime() # get date and time
The following code can be used to sleep, wake and check the reset cause:
import machine # check if the device woke from a deep sleep if machine.reset_cause() == machine.DEEPSLEEP_RESET: print('woke from a deep sleep') # put the device to sleep for 10 seconds machine.deepsleep(10000)
deepsleep()without an argument will put the device to sleep indefinitely
A software reset does not change the reset cause
There may be some leakage current flowing through enabled internal pullups. To further reduce power consumption it is possible to disable the internal pullups:
p1 = Pin(4, Pin.IN, Pin.PULL_HOLD)
After leaving deepsleep it may be necessary to un-hold the pin explicitly (e.g. if it is an output pin) via:
p1 = Pin(4, Pin.OUT, None)
The OneWire driver is implemented in software and works on all pins:
from machine import Pin import onewire ow = onewire.OneWire(Pin(12)) # create a OneWire bus on GPIO12 ow.scan() # return a list of devices on the bus ow.reset() # reset the bus ow.readbyte() # read a byte ow.writebyte(0x12) # write a byte on the bus ow.write('123') # write bytes on the bus ow.select_rom(b'12345678') # select a specific device by its ROM code
There is a specific driver for DS18S20 and DS18B20 devices:
import time, ds18x20 ds = ds18x20.DS18X20(ow) roms = ds.scan() ds.convert_temp() time.sleep_ms(750) for rom in roms: print(ds.read_temp(rom))
Be sure to put a 4.7k pull-up resistor on the data line. Note that
convert_temp() method must be called each time you want to
sample the temperature.
from machine import Pin from neopixel import NeoPixel pin = Pin(0, Pin.OUT) # set GPIO0 to output to drive NeoPixels np = NeoPixel(pin, 8) # create NeoPixel driver on GPIO0 for 8 pixels np = (255, 255, 255) # set the first pixel to white np.write() # write data to all pixels r, g, b = np # get first pixel colour
For low-level driving of a NeoPixel:
import esp esp.neopixel_write(pin, grb_buf, is800khz)
NeoPixel is configured to control the more popular 800kHz
units. It is possible to use alternative timing to control other (typically
400kHz) devices by passing
timing=0 when constructing the
TouchPad class in the
from machine import TouchPad, Pin t = TouchPad(Pin(14)) t.read() # Returns a smaller number when touched
TouchPad.read returns a value relative to the capacitive variation. Small numbers (typically in
the tens) are common when a pin is touched, larger numbers (above one thousand) when
no touch is present. However the values are relative and can vary depending on the board
and surrounding composition so some calibration may be required.
There are ten capacitive touch-enabled pins that can be used on the ESP32: 0, 2, 4, 12, 13
14, 15, 27, 32, 33. Trying to assign to any other pins will result in a
Note that TouchPads can be used to wake an ESP32 from sleep:
import machine from machine import TouchPad, Pin import esp32 t = TouchPad(Pin(14)) t.config(500) # configure the threshold at which the pin is considered touched esp32.wake_on_touch(True) machine.lightsleep() # put the MCU to sleep until a touchpad is touched
For more details on touchpads refer to Espressif Touch Sensor.
The DHT driver is implemented in software and works on all pins:
import dht import machine d = dht.DHT11(machine.Pin(4)) d.measure() d.temperature() # eg. 23 (°C) d.humidity() # eg. 41 (% RH) d = dht.DHT22(machine.Pin(4)) d.measure() d.temperature() # eg. 23.6 (°C) d.humidity() # eg. 41.3 (% RH)
WebREPL (web browser interactive prompt)¶
WebREPL (REPL over WebSockets, accessible via a web browser) is an experimental feature available in ESP32 port. Download web client from https://github.com/micropython/webrepl (hosted version available at http://micropython.org/webrepl), and configure it by executing:
and following on-screen instructions. After reboot, it will be available for connection. If you disabled automatic start-up on boot, you may run configured daemon on demand using:
import webrepl webrepl.start() # or, start with a specific password webrepl.start(password='mypass')
The WebREPL daemon listens on all active interfaces, which can be STA or AP. This allows you to connect to the ESP32 via a router (the STA interface) or directly when connected to its access point.
In addition to terminal/command prompt access, WebREPL also has provision
for file transfer (both upload and download). The web client has buttons for
the corresponding functions, or you can use the command-line client
webrepl_cli.py from the repository above.
See the MicroPython forum for other community-supported alternatives to transfer files to an ESP32 board.