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ESP-NOW-TX-RX

A very basic TX and RX demo for the ESP-NOW Protocol for the ESP8266 & ESP32

DUAL Mode RX/TX on 2 devices

FOR the ESP8266:

DualModeMaster : Has code for a master/server that sends a PING with a 200Byte data packet to the slave and prints the time in micros for it to return

DualModeSlave : Has code for a slave/node that waits for a PING with a 200Byte data packet and returns same

FOR the ESP32:

ESP32_DualMode_Master : Has code for a master/server that sends a PING with a 200Byte data packet to the slave and prints the time in micros for it to return

ESP32_DualMode_Slave : Has code for a slave/node that waits for a PING with a 200Byte data packet and returns same NOTES:

  • Im using the MAC addresses of my specific ESP32 modules, you will need t modify the code for your own:
  • The SLAVE Node needs to be initialized as a WIFI_AP you will need ot ge tits MAC via WiFi.softAPmacAddress()
  • THE MASTER Node needs to know the SLAVE Nodes WIFI_SOFT_AP MAC address (from the above comment)
  • You will need the MASTER nodes WIFI_STA MAC address via WiFi.macAddress()
  • The SLAVE needs the MASTER nodes WIFI_STA MAC address (from above line)
  • YOU MUST indicate on the SLAVE NODE that the MASTER node is using the ESP_IF_WIFI_AP interface for ESPNOW via master.ifidx = ESP_IF_WIFI_AP; on line 38

Setup Instructions FOR the ESP8266

If you are using Arduino IDE you need to do the following before compiling:

  1. Make sure you have the LATEST espnow.h file get it form here https://github.com/esp8266/Arduino/blob/d24a358817f0c11f7087b3c8acbf24629b15998f/tools/sdk/include/espnow.h and replace what you have in C:\Users\YOUR_USER_NAME\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.3.0\tools\sdk\include

  2. Open the file C:\Users\YOUR_USER_NAME\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.3.0\platform.txt find the line that starts with "compiler.c.elf.libs" add the following(without talking marks) to the END OF THE LINE and save "-lespnow"

Things I found deep in the rabbit hole

  • Espressif docs state that the maximum payload per frame is 250 bytes. On the ESP8266 I found that 200 bytes is the real maximum. Anything over 200 bytes will return an error. On the ESP32 you CAN send 250 bytes.
  • Broadcasting does not work in the sense that you would expect it to. In the ESP32 branch of this code, you can add 1 peer with a mac adrress of FF:FF:FF:FF:FF:FF and any data sent to that peer SHOULD theoreticaly transmit to ALL devices on that chanel. This is not the case on the ESP8266. You can iether add a bunch of peers and cycle though them to send the same data OR set each peers MAC address to the be the same VIA:
 extern "C"{
   #include <espnow.h>
   #include "user_interface.h"
 }
 uint8_t mac[] = {0x36, 0x33, 0x33, 0x33, 0x33, 0x33};
 void initVariant()
 {
   wifi_set_macaddr(STATION_IF, &mac[0]);
 }

  • Espressif docs state that sending data to "NULL" is also a broadcast, however this does NOT work for the ESP8266, But DOES work on the ESP32

  • ESP-Now Seems to work between devices. I have testes an ESP8266 as a TX to an ESP32 as an RX, but there seemed to be iether dropped frames or delays in receiveing frames

For the ESP32 read espressif/esp-idf#3238 for very detailed explanantion of espnow speeds and ways to controll them using the espidf example code here https://github.com/leonyuhanov/ESP32_ESPIDF_ESPNOW