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$3 ESP-01 (ESP8266) module from Price Minister

Hardware

Arduino Code

#define WIFI_CH_PD 5

void setup(void)  {
  digitalWrite(WIFI_CH_PD, LOW);
  delay(500);
  digitalWrite(WIFI_CH_PD, HIGH);
  delay(2000);
  Serial.begin(115200);  
}
void loop(void) {
  Serial.println("AT");
  //while (!Serial.available()) {}
  while (Serial.available()) {
    char c = Serial.read();
    display.print(c);
  }
  display.println("");
  delay(2000);
}