RX pin keeps output 3.3V
Posted: Thu Oct 22, 2020 8:03 pmHi, I got a WeMos D1 mini (ESP-12F dev board) board and loaded the AT firmware from Espressif website. The board itself responds to AT commands from Arduino serial monitor. Now I am trying to test throwing AT commands from Arduino Uno via SoftwareSerial to ESP board while connecting serial pins of both. The boards connections are like this.
Arduino ESP
---------------------------------------
5V ----------------------------- 5V
D11 (TX) ------- VD -------- RX
D10 (RX) -------------------- TX
GND ------------------------ GND
"VD" in the above diagram is a voltage divider circuit to drop 5V high logic to 3.3V as shown in this web site.
https://homediyelectronics.com/projects ... converter/
With this configuration, I was able to monitor on Arduino the startup message, though garbled, from ESP that is generated at boot. However, ESP does not respond to AT commands from Arduino. It looks like the TX signal is not reaching ESP RX.
To troubleshoot further, I programmed 1Hz high/low flip-flop signal on D11 (TX) and monitored the voltage on the line. Though D11 keeps switching 5V and 0V, RX on ESP is constantly kept 3.3V. I completely disconnected VD/RX connection, then tap voltage in VD is switching 3.3V and 0V. I suspected ESP RX pin. It constantly output 3.3V. (I don't have an ossiloscope but measured with digital multimeter).
I think RX pin on ESP should be nothing more than digital input and kept in high impedance. Am I wrong?
Arduino ESP
---------------------------------------
5V ----------------------------- 5V
D11 (TX) ------- VD -------- RX
D10 (RX) -------------------- TX
GND ------------------------ GND
"VD" in the above diagram is a voltage divider circuit to drop 5V high logic to 3.3V as shown in this web site.
https://homediyelectronics.com/projects ... converter/
With this configuration, I was able to monitor on Arduino the startup message, though garbled, from ESP that is generated at boot. However, ESP does not respond to AT commands from Arduino. It looks like the TX signal is not reaching ESP RX.
To troubleshoot further, I programmed 1Hz high/low flip-flop signal on D11 (TX) and monitored the voltage on the line. Though D11 keeps switching 5V and 0V, RX on ESP is constantly kept 3.3V. I completely disconnected VD/RX connection, then tap voltage in VD is switching 3.3V and 0V. I suspected ESP RX pin. It constantly output 3.3V. (I don't have an ossiloscope but measured with digital multimeter).
I think RX pin on ESP should be nothing more than digital input and kept in high impedance. Am I wrong?