Because there is no suitable pin on my esp8266 to connect to the lcd, I want to transmit the data on the esp8266 to the uno through TX/RX, and let the uno display the received data on the lcd.
Sounds like a plan.
But if you want help maybe tell us what ESP8266 variant that you have. And what LCD and what interface the LCD uses.
esp8266:wemos d1 mini
lcd:16x2 i2c
You only need 2 pins on the ESP for the LCD. You would need at least one, if not 2, for the serial communications. So why not use the I2C on the ESP for the LCD? It would be less complicated to do that than interface the serial ports of the 3.3V ESP to the 5V Uno.
If the default I2C pins (D4 & D5) are already used, you can use different pins for I2C. The Wire library for the ESP8266 allows one to select the I2C pins.
because my esp i2c to use the max30100，so no pin to use the lcd
Isn't the MAX30100 an I2C device? Are you aware that I2C is a bus that to which many different devices may connect. All devices on the bus share the SDA and SCL pins. The devices each have a unique address. How the I2C bus works.
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