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`espnow` — support for the ESP-NOW wireless protocol¶

This module provides an interface to the ESP-NOW protocol provided by Espressif on ESP32 and ESP8266 devices (API docs).

Table of Contents:¶

Introduction

Configuration

Sending and Receiving Data

Peer Management

Callback Methods

Exceptions

Constants

Wifi Signal Strength (RSSI) - (ESP32 Only)

Supporting asyncio

Broadcast and Multicast

ESPNow and Wifi Operation

ESPNow and Sleep Modes

Introduction¶

ESP-NOW is a connection-less wireless communication protocol supporting:

Direct communication between up to 20 registered peers:
- Without the need for a wireless access point (AP),
Encrypted and unencrypted communication (up to 6 encrypted peers),
Message sizes up to 250 bytes,
Can operate alongside Wifi operation (network.WLAN) on ESP32 and ESP8266 devices.

It is especially useful for small IoT networks, latency sensitive or power sensitive applications (such as battery operated devices) and for long-range communication between devices (hundreds of metres).

This module also supports tracking the Wifi signal strength (RSSI) of peer devices.

A simple example would be:

Sender:

import network
import espnow

# A WLAN interface must be active to send()/recv()
sta = network.WLAN(network.WLAN.IF_STA)  # Or network.WLAN.IF_AP
sta.active(True)
sta.disconnect()      # For ESP8266

e = espnow.ESPNow()
e.active(True)
peer = b'\xbb\xbb\xbb\xbb\xbb\xbb'   # MAC address of peer's wifi interface
e.add_peer(peer)      # Must add_peer() before send()

e.send(peer, "Starting...")
for i in range(100):
    e.send(peer, str(i)*20, True)
e.send(peer, b'end')

Receiver:

import network
import espnow

# A WLAN interface must be active to send()/recv()
sta = network.WLAN(network.WLAN.IF_STA)
sta.active(True)
sta.disconnect()   # Because ESP8266 auto-connects to last Access Point

e = espnow.ESPNow()
e.active(True)

while True:
    host, msg = e.recv()
    if msg:             # msg == None if timeout in recv()
        print(host, msg)
        if msg == b'end':
            break

class ESPNow¶

Constructor¶

class espnow.ESPNow¶: Returns the singleton ESPNow object. As this is a singleton, all calls to espnow.ESPNow() return a reference to the same object.

Note

Some methods are available only on the ESP32 due to code size restrictions on the ESP8266 and differences in the Espressif API.

Configuration¶

ESPNow.active([flag])¶

Initialise or de-initialise the ESP-NOW communication protocol depending on the value of the flag optional argument.

Arguments:

flag: Any python value which can be converted to a boolean type.
- True: Prepare the software and hardware for use of the ESP-NOW communication protocol, including:
  - initialise the ESPNow data structures,
  - allocate the recv data buffer,
  - invoke esp_now_init() and
  - register the send and recv callbacks.
- False: De-initialise the Espressif ESP-NOW software stack (esp_now_deinit()), disable callbacks, deallocate the recv data buffer and deregister all peers.

If flag is not provided, return the current status of the ESPNow interface.

Returns:: True if interface is currently active, else False.

ESPNow.config(param=value, ...)¶

ESPNow.config('param') (ESP32 only)

Set or get configuration values of the ESPNow interface. To set values, use the keyword syntax, and one or more parameters can be set at a time. To get a value the parameter name should be quoted as a string, and just one parameter is queried at a time.

Note: Getting parameters is not supported on the ESP8266.

Options:

rxbuf: (default=526) Get/set the size in bytes of the internal buffer used to store incoming ESPNow packet data. The default size is selected to fit two max-sized ESPNow packets (250 bytes) with associated mac_address (6 bytes), a message byte count (1 byte) and RSSI data plus buffer overhead. Increase this if you expect to receive a lot of large packets or expect bursty incoming traffic.

Note: The recv buffer is allocated by ESPNow.active(). Changing this value will have no effect until the next call of ESPNow.active(True).

timeout_ms: (default=300,000) Default timeout (in milliseconds) for receiving ESPNow messages. If timeout_ms is less than zero, then wait forever. The timeout can also be provided as arg to recv()/irecv()/recvinto().

rate: (ESP32 only, IDF>=4.3.0 only) Set the transmission speed for ESPNow packets. Must be set to a number from the allowed numeric values in enum wifi_phy_rate_t.

Returns:: None or the value of the parameter being queried.

Raises:

OSError(num, "ESP_ERR_ESPNOW_NOT_INIT") if not initialised.
ValueError() on invalid configuration options or values.

Sending and Receiving Data¶

A wifi interface (network.WLAN.IF_STA or network.WLAN.IF_AP) must be active() before messages can be sent or received, but it is not necessary to connect or configure the WLAN interface. For example:

import network

sta = network.WLAN(network.WLAN.IF_STA)
sta.active(True)
sta.disconnect()    # For ESP8266

Note: The ESP8266 has a feature that causes it to automatically reconnect to the last wifi Access Point when set active(True) (even after reboot/reset). This reduces the reliability of receiving ESP-NOW messages (see ESPNow and Wifi Operation). You can avoid this by calling disconnect() after active(True).

ESPNow.send(mac, msg[, sync])¶

ESPNow.send(msg) (ESP32 only)

Send the data contained in msg to the peer with given network mac address. In the second form, mac=None and sync=True. The peer must be registered with ESPNow.add_peer() before the message can be sent.

Arguments:

mac: byte string exactly espnow.ADDR_LEN (6 bytes) long or None. If mac is None (ESP32 only) the message will be sent to all registered peers, except any broadcast or multicast MAC addresses.
msg: string or byte-string up to espnow.MAX_DATA_LEN (250) bytes long.
sync:
- True: (default) send msg to the peer(s) and wait for a response (or not).
- False send msg and return immediately. Responses from the peers will be discarded.

Returns:: True if sync=False or if sync=True and all peers respond, else False.

Raises:

OSError(num, "ESP_ERR_ESPNOW_NOT_INIT") if not initialised.
OSError(num, "ESP_ERR_ESPNOW_NOT_FOUND") if peer is not registered.
OSError(num, "ESP_ERR_ESPNOW_IF") the wifi interface is not active().
OSError(num, "ESP_ERR_ESPNOW_NO_MEM") internal ESP-NOW buffers are full.
ValueError() on invalid values for the parameters.

Note: A peer will respond with success if its wifi interface is active() and set to the same channel as the sender, regardless of whether it has initialised it’s ESP-NOW system or is actively listening for ESP-NOW traffic (see the Espressif ESP-NOW docs).

ESPNow.recv([timeout_ms])¶

Wait for an incoming message and return the mac address of the peer and the message. Note: It is not necessary to register a peer (using add_peer()) to receive a message from that peer.

Arguments:

timeout_ms: (Optional): May have the following values.
- 0: No timeout. Return immediately if no data is available;
- > 0: Specify a timeout value in milliseconds;
- < 0: Do not timeout, ie. wait forever for new messages; or
- None (or not provided): Use the default timeout value set with ESPNow.config().

Returns:

(None, None) if timeout is reached before a message is received, or
[mac, msg]: where:
- mac is a bytestring containing the address of the device which sent the message, and
- msg is a bytestring containing the message.

Raises:

OSError(num, "ESP_ERR_ESPNOW_NOT_INIT") if not initialised.
OSError(num, "ESP_ERR_ESPNOW_IF") if the wifi interface is not active().
ValueError() on invalid timeout_ms values.

ESPNow.recv() will allocate new storage for the returned list and the peer and msg bytestrings. This can lead to memory fragmentation if the data rate is high. See ESPNow.irecv() for a memory-friendly alternative.

ESPNow.irecv([timeout_ms])¶

Works like ESPNow.recv() but will reuse internal bytearrays to store the return values: [mac, msg], so that no new memory is allocated on each call.

Arguments:: timeout_ms: (Optional) Timeout in milliseconds (see ESPNow.recv()).

Returns:

As for ESPNow.recv(), except that msg is a bytearray, instead of a bytestring. On the ESP8266, mac will also be a bytearray.

Raises:

See ESPNow.recv().

Note: You may also read messages by iterating over the ESPNow object, which will use the irecv() method for alloc-free reads, eg:

import espnow
e = espnow.ESPNow(); e.active(True)
for mac, msg in e:
    print(mac, msg)
    if mac is None:   # mac, msg will equal (None, None) on timeout
        break

ESPNow.recvinto(data[, timeout_ms])¶

Wait for an incoming message and return the length of the message in bytes. This is the low-level method used by both recv() and irecv() to read messages.

Arguments:

data: A list of at least two elements, [peer, msg]. msg must be a bytearray large enough to hold the message (250 bytes). On the ESP8266, peer should be a bytearray of 6 bytes. The MAC address of the sender and the message will be stored in these bytearrays (see Note on ESP32 below).

timeout_ms: (Optional) Timeout in milliseconds (see ESPNow.recv()).

Returns:

Length of message in bytes or 0 if timeout_ms is reached before a message is received.

Raises:

See ESPNow.recv().

Note: On the ESP32:

It is unnecessary to provide a bytearray in the first element of the data list because it will be replaced by a reference to a unique peer address in the peer device table (see ESPNow.peers_table).
If the list is at least 4 elements long, the rssi and timestamp values will be saved as the 3rd and 4th elements.

ESPNow.any()¶

Check if data is available to be read with ESPNow.recv().

For more sophisticated querying of available characters use select.poll():

import select
import espnow

e = espnow.ESPNow()
poll = select.poll()
poll.register(e, select.POLLIN)
poll.poll(timeout)

Returns:: True if data is available to be read, else False.

ESPNow.stats() (ESP32 only)¶

Returns:

A 5-tuple containing the number of packets sent/received/lost:

(tx_pkts, tx_responses, tx_failures, rx_packets, rx_dropped_packets)

Incoming packets are dropped when the recv buffers are full. To reduce packet loss, increase the rxbuf config parameters and ensure you are reading messages as quickly as possible.

Note: Dropped packets will still be acknowledged to the sender as received.

Peer Management¶

On ESP32 devices, the Espressif ESP-NOW software requires that other devices (peers) must be registered using add_peer() before we can send() them messages (this is not enforced on ESP8266 devices). It is not necessary to register a peer to receive an un-encrypted message from that peer.

Encrypted messages: To receive an encrypted message, the receiving device must first register the sender and use the same encryption keys as the sender (PMK and LMK) (see set_pmk() and add_peer().

ESPNow.set_pmk(pmk)¶

Set the Primary Master Key (PMK) which is used to encrypt the Local Master Keys (LMK) for encrypting messages. If this is not set, a default PMK is used by the underlying Espressif ESP-NOW software stack.

Note: messages will only be encrypted if lmk is also set in ESPNow.add_peer() (see Security in the Espressif API docs).

Arguments:: pmk: Must be a byte string, bytearray or string of length espnow.KEY_LEN (16 bytes).

Returns:: None

Raises:: ValueError() on invalid pmk values.

ESPNow.add_peer(mac[, lmk][, channel][, ifidx][, encrypt])¶

ESPNow.add_peer(mac, param=value, ...) (ESP32 only)

Add/register the provided mac address as a peer. Additional parameters may also be specified as positional or keyword arguments (any parameter set to None will be set to it’s default value):

Arguments:

mac: The MAC address of the peer (as a 6-byte byte-string).
lmk: The Local Master Key (LMK) key used to encrypt data transfers with this peer (unless the encrypt parameter is set to False). Must be:
- a byte-string or bytearray or string of length espnow.KEY_LEN (16 bytes), or
- any non True python value (default= b''), signifying an empty key which will disable encryption.
channel: The wifi channel (2.4GHz) to communicate with this peer. Must be an integer from 0 to 14. If channel is set to 0 the current channel of the wifi device will be used, if channel is set to another value then this must match the channel currently configured on the interface (see WLAN.config()). (default=0)
ifidx: (ESP32 only) Index of the wifi interface which will be used to send data to this peer. Must be an integer set to network.WLAN.IF_STA (=0) or network.WLAN.IF_AP (=1). (default=0/network.WLAN.IF_STA). See ESPNow and Wifi Operation below for more information.
encrypt: (ESP32 only) If set to True data exchanged with this peer will be encrypted with the PMK and LMK. (default = True if lmk is set to a valid key, else False)

ESP8266: Keyword args may not be used on the ESP8266.

Note: The maximum number of peers which may be registered is 20 (espnow.MAX_TOTAL_PEER_NUM), with a maximum of 6 (espnow.MAX_ENCRYPT_PEER_NUM) of those peers with encryption enabled (see ESP_NOW_MAX_ENCRYPT_PEER_NUM in the Espressif API docs).

Raises:

OSError(num, "ESP_ERR_ESPNOW_NOT_INIT") if not initialised.
OSError(num, "ESP_ERR_ESPNOW_EXIST") if mac is already registered.
OSError(num, "ESP_ERR_ESPNOW_FULL") if too many peers are already registered.
OSError(num, "ESP_ERR_ESPNOW_CHAN") if a channel value was set that doesn’t match the channel currently configured for this interface.
ValueError() on invalid keyword args or values.

ESPNow.del_peer(mac)¶

Deregister the peer associated with the provided mac address.

Returns:: None

Raises:

OSError(num, "ESP_ERR_ESPNOW_NOT_INIT") if not initialised.
OSError(num, "ESP_ERR_ESPNOW_NOT_FOUND") if mac is not registered.
ValueError() on invalid mac values.

ESPNow.get_peer(mac) (ESP32 only)¶

Return information on a registered peer.

Returns:: (mac, lmk, channel, ifidx, encrypt): a tuple of the “peer info” associated with the given mac address.

Raises:

OSError(num, "ESP_ERR_ESPNOW_NOT_INIT") if not initialised.
OSError(num, "ESP_ERR_ESPNOW_NOT_FOUND") if mac is not registered.
ValueError() on invalid mac values.

ESPNow.peer_count() (ESP32 only)¶

Return the number of registered peers:

(peer_num, encrypt_num): where
- peer_num is the number of peers which are registered, and
- encrypt_num is the number of encrypted peers.

ESPNow.get_peers() (ESP32 only)¶: Return the “peer info” parameters for all the registered peers (as a tuple of tuples).

ESPNow.mod_peer(mac, lmk, [channel], [ifidx], [encrypt]) (ESP32 only)¶
ESPNow.mod_peer(mac, 'param'=value, ...) (ESP32 only): Modify the parameters of the peer associated with the provided mac address. Parameters may be provided as positional or keyword arguments (see ESPNow.add_peer()). Any parameter that is not set (or set to None) will retain the existing value for that parameter.

Callback Methods¶

ESPNow.irq(callback) (ESP32 only)¶

Set a callback function to be called as soon as possible after a message has been received from another ESPNow device. The callback function will be called with the ESPNow instance object as an argument. For more reliable operation, it is recommended to read out as many messages as are available when the callback is invoked and to set the read timeout to zero, eg:

def recv_cb(e):
    while True:  # Read out all messages waiting in the buffer
        mac, msg = e.irecv(0)  # Don't wait if no messages left
        if mac is None:
            return
        print(mac, msg)
e.irq(recv_cb)

The irq() callback method is an alternative method for processing incoming messages, especially if the data rate is moderate and the device is not too busy but there are some caveats:

The scheduler stack can overflow and callbacks will be missed if packets are arriving at a sufficient rate or if other MicroPython components (eg, bluetooth, machine.Pin.irq(), machine.timer, i2s, …) are exercising the scheduler stack. This method may be less reliable for dealing with bursts of messages, or high throughput or on a device which is busy dealing with other hardware operations.
For more information on scheduled function callbacks see: micropython.schedule().

Constants¶

espnow.MAX_DATA_LEN(=250)¶
espnow.KEY_LEN(=16)¶
espnow.ADDR_LEN(=6)¶
espnow.MAX_TOTAL_PEER_NUM(=20)¶
espnow.MAX_ENCRYPT_PEER_NUM(=6)¶

Exceptions¶

If the underlying Espressif ESP-NOW software stack returns an error code, the MicroPython espnow module will raise an OSError(errnum, errstring) exception where errstring is set to the name of one of the error codes identified in the Espressif ESP-NOW docs. For example:

try:
    e.send(peer, 'Hello')
except OSError as err:
    if len(err.args) < 2:
        raise err
    if err.args[1] == 'ESP_ERR_ESPNOW_NOT_INIT':
        e.active(True)
    elif err.args[1] == 'ESP_ERR_ESPNOW_NOT_FOUND':
        e.add_peer(peer)
    elif err.args[1] == 'ESP_ERR_ESPNOW_IF':
        network.WLAN(network.WLAN.IF_STA).active(True)
    else:
        raise err

Wifi Signal Strength (RSSI) - (ESP32 only)¶

The ESPNow object maintains a peer device table which contains the signal strength and timestamp of the last received message from all hosts. The peer device table can be accessed using ESPNow.peers_table and can be used to track device proximity and identify nearest neighbours in a network of peer devices. This feature is not available on ESP8266 devices.

ESPNow.peers_table¶

A reference to the peer device table: a dict of known peer devices and rssi values:

{peer: [rssi, time_ms], ...}

where:

peer is the peer MAC address (as bytes);
rssi is the wifi signal strength in dBm (-127 to 0) of the last message received from the peer; and
time_ms is the time the message was received (in milliseconds since system boot - wraps every 12 days).

Example:

>>> e.peers_table
{b'\xaa\xaa\xaa\xaa\xaa\xaa': [-31, 18372],
 b'\xbb\xbb\xbb\xbb\xbb\xbb': [-43, 12541]}

Note: the mac addresses returned by recv() are references to the peer key values in the peer device table.

Note: RSSI and timestamp values in the device table are updated only when the message is read by the application.

Supporting asyncio¶

A supplementary module (aioespnow) is available to provide asyncio support.

Note: Asyncio support is available on all ESP32 targets as well as those ESP8266 boards which include the asyncio module (ie. ESP8266 devices with at least 2MB flash memory).

A small async server example:

import network
import aioespnow
import asyncio

# A WLAN interface must be active to send()/recv()
network.WLAN(network.WLAN.IF_STA).active(True)

e = aioespnow.AIOESPNow()  # Returns AIOESPNow enhanced with async support
e.active(True)
peer = b'\xbb\xbb\xbb\xbb\xbb\xbb'
e.add_peer(peer)

# Send a periodic ping to a peer
async def heartbeat(e, peer, period=30):
    while True:
        if not await e.asend(peer, b'ping'):
            print("Heartbeat: peer not responding:", peer)
        else:
            print("Heartbeat: ping", peer)
        await asyncio.sleep(period)

# Echo any received messages back to the sender
async def echo_server(e):
    async for mac, msg in e:
        print("Echo:", msg)
        try:
            await e.asend(mac, msg)
        except OSError as err:
            if len(err.args) > 1 and err.args[1] == 'ESP_ERR_ESPNOW_NOT_FOUND':
                e.add_peer(mac)
                await e.asend(mac, msg)

async def main(e, peer, timeout, period):
    asyncio.create_task(heartbeat(e, peer, period))
    asyncio.create_task(echo_server(e))
    await asyncio.sleep(timeout)

asyncio.run(main(e, peer, 120, 10))

class aioespnow.AIOESPNow¶: The AIOESPNow class inherits all the methods of ESPNow and extends the interface with the following async methods.

async AIOESPNow.arecv(): Asyncio support for ESPNow.recv(). Note that this method does not take a timeout value as argument.

async AIOESPNow.airecv(): Asyncio support for ESPNow.irecv(). Note that this method does not take a timeout value as argument.

async AIOESPNow.asend(mac, msg, sync=True)
async AIOESPNow.asend(msg): Asyncio support for ESPNow.send().

AIOESPNow._aiter__() / async AIOESPNow.__anext__()¶

AIOESPNow also supports reading incoming messages by asynchronous iteration using async for; eg:

e = AIOESPNow()
e.active(True)
async def recv_till_halt(e):
    async for mac, msg in e:
        print(mac, msg)
        if msg == b'halt':
          break
asyncio.run(recv_till_halt(e))

Broadcast and Multicast¶

All active ESPNow clients will receive messages sent to their MAC address and all devices (except ESP8266 devices) will also receive messages sent to the broadcast MAC address (b'\xff\xff\xff\xff\xff\xff') or any multicast MAC address.

All ESPNow devices (including ESP8266 devices) can also send messages to the broadcast MAC address or any multicast MAC address.

To send() a broadcast message, the broadcast (or multicast) MAC address must first be registered using add_peer(). send() will always return True for broadcasts, regardless of whether any devices receive the message. It is not permitted to encrypt messages sent to the broadcast address or any multicast address.

Note: ESPNow.send(None, msg) will send to all registered peers except the broadcast address. To send a broadcast or multicast message, you must specify the broadcast (or multicast) MAC address as the peer. For example:

bcast = b'\xff' * 6
e.add_peer(bcast)
e.send(bcast, "Hello World!")

ESPNow and Wifi Operation¶

ESPNow messages may be sent and received on any active() WLAN interface (network.WLAN.IF_STA or network.WLAN.IF_AP), even if that interface is also connected to a wifi network or configured as an access point. When an ESP32 or ESP8266 device connects to a Wifi Access Point (see ESP32 Quickref) the following things happen which affect ESPNow communications:

Wifi Power-saving Mode (network.WLAN.PM_PERFORMANCE) is automatically activated and
The radio on the esp device changes wifi channel to match the channel used by the Access Point.

Wifi Power-saving Mode: (see Espressif Docs) The power saving mode causes the device to turn off the radio periodically (typically for hundreds of milliseconds), making it unreliable in receiving ESPNow messages. This can be resolved by either of:

Disabling the power-saving mode on the STA_IF interface;
- Use sta.config(pm=sta.PM_NONE)
Turning on the AP_IF interface, which will disable the power saving mode. However, the device will then be advertising an active wifi access point.
- You may also choose to send your messages via the AP_IF interface, but this is not necessary.
- ESP8266 peers must send messages to this AP_IF interface (see below).
Configuring ESPNow clients to retry sending messages.

Receiving messages from an ESP8266 device: Strangely, an ESP32 device connected to a wifi network using method 1 or 2 above, will receive ESPNow messages sent to the STA_IF MAC address from another ESP32 device, but will reject messages from an ESP8266 device!!!. To receive messages from an ESP8266 device, the AP_IF interface must be set to active(True) and messages must be sent to the AP_IF MAC address.

Managing wifi channels: Any other ESPNow devices wishing to communicate with a device which is also connected to a Wifi Access Point MUST use the same channel. A common scenario is where one ESPNow device is connected to a wifi router and acts as a proxy for messages from a group of sensors connected via ESPNow:

Proxy:

import network, time, espnow

sta, ap = wifi_reset()  # Reset wifi to AP off, STA on and disconnected
sta.connect('myssid', 'mypassword')
while not sta.isconnected():  # Wait until connected...
    time.sleep(0.1)
sta.config(pm=sta.PM_NONE)  # ..then disable power saving

# Print the wifi channel used AFTER finished connecting to access point
print("Proxy running on channel:", sta.config("channel"))
e = espnow.ESPNow(); e.active(True)
for peer, msg in e:
    # Receive espnow messages and forward them to MQTT broker over wifi

Sensor:

import network, espnow

sta, ap = wifi_reset()   # Reset wifi to AP off, STA on and disconnected
sta.config(channel=6)    # Change to the channel used by the proxy above.
peer = b'0\xaa\xaa\xaa\xaa\xaa'  # MAC address of proxy
e = espnow.ESPNow(); e.active(True);
e.add_peer(peer)
while True:
    msg = read_sensor()
    e.send(peer, msg)
    time.sleep(1)

Other issues to take care with when using ESPNow with wifi are:

Set WIFI to known state on startup: MicroPython does not reset the wifi peripheral after a soft reset. This can lead to unexpected behaviour. To guarantee the wifi is reset to a known state after a soft reset make sure you deactivate the STA_IF and AP_IF before setting them to the desired state at startup, eg.:

import network, time

def wifi_reset():   # Reset wifi to AP_IF off, STA_IF on and disconnected
  sta = network.WLAN(network.WLAN.IF_STA); sta.active(False)
  ap = network.WLAN(network.WLAN.IF_AP); ap.active(False)
  sta.active(True)
  while not sta.active():
      time.sleep(0.1)
  sta.disconnect()   # For ESP8266
  while sta.isconnected():
      time.sleep(0.1)
  return sta, ap

sta, ap = wifi_reset()

Remember that a soft reset occurs every time you connect to the device REPL and when you type ctrl-D.

STA_IF and AP_IF always operate on the same channel: the AP_IF will change channel when you connect to a wifi network; regardless of the channel you set for the AP_IF (see Attention Note 3 ). After all, there is really only one wifi radio on the device, which is shared by the STA_IF and AP_IF virtual devices.
Disable automatic channel assignment on your wifi router: If the wifi router for your wifi network is configured to automatically assign the wifi channel, it may change the channel for the network if it detects interference from other wifi routers. When this occurs, the ESP devices connected to the wifi network will also change channels to match the router, but other ESPNow-only devices will remain on the previous channel and communication will be lost. To mitigate this, either set your wifi router to use a fixed wifi channel or configure your devices to re-scan the wifi channels if they are unable to find their expected peers on the current channel.
MicroPython re-scans wifi channels when trying to reconnect: If the esp device is connected to a Wifi Access Point that goes down, MicroPython will automatically start scanning channels in an attempt to reconnect to the Access Point. This means ESPNow messages will be lost while scanning for the AP. This can be disabled by sta.config(reconnects=0), which will also disable the automatic reconnection after losing connection.
Some versions of the ESP IDF only permit sending ESPNow packets from the STA_IF interface to peers which have been registered on the same wifi channel as the STA_IF:
```
ESPNOW: Peer channel is not equal to the home channel, send fail!
```

ESPNow and Sleep Modes¶

The machine.lightsleep([time_ms]) and machine.deepsleep([time_ms]) functions can be used to put the ESP32 and peripherals (including the WiFi and Bluetooth radios) to sleep. This is useful in many applications to conserve battery power. However, applications must disable the WLAN peripheral (using active(False)) before entering light or deep sleep (see Sleep Modes). Otherwise the WiFi radio may not be initialised properly after wake from sleep. If the STA_IF and AP_IF interfaces have both been set active(True) then both interfaces should be set active(False) before entering any sleep mode.

Example: deep sleep:

import network, machine, espnow

sta, ap = wifi_reset()            # Reset wifi to AP off, STA on and disconnected
peer = b'0\xaa\xaa\xaa\xaa\xaa'   # MAC address of peer
e = espnow.ESPNow()
e.active(True)
e.add_peer(peer)                  # Register peer on STA_IF

print('Sending ping...')
if not e.send(peer, b'ping'):
  print('Ping failed!')
e.active(False)
sta.active(False)                 # Disable the wifi before sleep
print('Going to sleep...')
machine.deepsleep(10000)          # Sleep for 10 seconds then reboot

Example: light sleep:

import network, machine, espnow

sta, ap = wifi_reset()            # Reset wifi to AP off, STA on and disconnected
sta.config(channel=6)
peer = b'0\xaa\xaa\xaa\xaa\xaa'   # MAC address of peer
e = espnow.ESPNow()
e.active(True)
e.add_peer(peer)                  # Register peer on STA_IF

while True:
  print('Sending ping...')
  if not e.send(peer, b'ping'):
    print('Ping failed!')
  sta.active(False)               # Disable the wifi before sleep
  print('Going to sleep...')
  machine.lightsleep(10000)       # Sleep for 10 seconds
  sta.active(True)
  sta.config(channel=6)           # Wifi loses config after lightsleep()

espnow — support for the ESP-NOW wireless protocol¶

Table of Contents:¶

Introduction¶

class ESPNow¶

Constructor¶

Configuration¶

Sending and Receiving Data¶

Peer Management¶

Callback Methods¶

Constants¶

Exceptions¶

Wifi Signal Strength (RSSI) - (ESP32 only)¶

Supporting asyncio¶

Broadcast and Multicast¶

ESPNow and Wifi Operation¶

ESPNow and Sleep Modes¶

`espnow` — support for the ESP-NOW wireless protocol¶