ESP-NOW on two NodeMCUs

// ESP-NOW on the ESP8266: a count and a knob reading every two seconds to the other board.
//
// The ESP8266 core's espnow.h, as the NodeMCU tutorials use it: a role, a
// peer added with its channel, and a send callback that gets 0 when the
// receiver's radio acknowledged the frame. The receiver's MAC is written
// below; in this project its wifiMac setting is that address.

#include <ESP8266WiFi.h>
#include <espnow.h>

uint8_t receiverMac[] = {0x02, 0x4D, 0x4F, 0x00, 0x82, 0x66};

typedef struct {
    char text[32];
    int count;
    int dial; // the knob on A0, 0 to 1023
} Message;

Message msg;
unsigned long lastSend = 0;

void onSent(uint8_t *mac, uint8_t status)
{
    (void)mac;
    Serial.print("Last packet send status: ");
    Serial.println(status == 0 ? "Delivery success" : "Delivery fail");
}

void setup()
{
    Serial.begin(115200);
    WiFi.mode(WIFI_STA);
    Serial.print("Sender MAC: ");
    Serial.println(WiFi.macAddress());

    if (esp_now_init() != 0) {
        Serial.println("Error initializing ESP-NOW");
        return;
    }
    esp_now_set_self_role(ESP_NOW_ROLE_CONTROLLER);
    esp_now_register_send_cb(onSent);
    esp_now_add_peer(receiverMac, ESP_NOW_ROLE_SLAVE, 1, NULL, 0);
}

void loop()
{
    if (millis() - lastSend > 2000) {
        lastSend = millis();
        strcpy(msg.text, "hello from the NodeMCU");
        msg.count++;
        msg.dial = analogRead(A0);
        esp_now_send(receiverMac, (uint8_t *)&msg, sizeof(msg));
    }
}

// ESP-NOW on the ESP8266: prints what the other board sends.
//
// It prints its own MAC first, the address the sender writes into its sketch
// (in this project the board's wifiMac setting, 02:4D:4F:00:82:66). The
// on-board LED on D4 is active low and blinks once for each message.

#include <ESP8266WiFi.h>
#include <espnow.h>

typedef struct {
    char text[32];
    int count;
    int dial;
} Message;

volatile bool got = false;

void onReceive(uint8_t *mac, uint8_t *data, uint8_t len)
{
    Message msg;
    if (len != sizeof(msg)) return;
    memcpy(&msg, data, sizeof(msg));
    Serial.printf("From %02X:%02X:%02X:%02X:%02X:%02X, %u bytes: %s, count %d, dial %d\n", mac[0], mac[1], mac[2],
                  mac[3], mac[4], mac[5], len, msg.text, msg.count, msg.dial);
    got = true;
}

void setup()
{
    Serial.begin(115200);
    pinMode(LED_BUILTIN, OUTPUT);
    digitalWrite(LED_BUILTIN, HIGH);
    WiFi.mode(WIFI_STA);
    Serial.print("Receiver MAC: ");
    Serial.println(WiFi.macAddress());

    if (esp_now_init() != 0) {
        Serial.println("Error initializing ESP-NOW");
        return;
    }
    esp_now_set_self_role(ESP_NOW_ROLE_SLAVE);
    esp_now_register_recv_cb(onReceive);
}

void loop()
{
    if (got) {
        got = false;
        digitalWrite(LED_BUILTIN, LOW);
        delay(100);
        digitalWrite(LED_BUILTIN, HIGH);
    }
}