Comments on: ESP32 UART Communication (Serial): Set Pins, Interfaces, Send and Receive Data (Arduino IDE)

By: Sara Santos

Sara Santos — Sun, 26 Apr 2026 20:26:56 +0000

In reply to Mark.

You can use those pins. But, you won’t be able to use the serial monitor.
Those pins are also used to upload code to the board. So, if they are being used for serial comunication with a sensor, then, you must reset the ESP32 afterwards if you want to upload new code.
Regards,
Sara

By: Mark

Mark — Tue, 21 Apr 2026 07:36:52 +0000

In reply to Sara Santos. Is there a problem if I use the pins 1 and 3?

By: Beat

Beat — Mon, 16 Feb 2026 14:07:40 +0000

Hi,
due to the fact that you are the most skilled Arduino ESP guys I know, I have maybe a challenge for you…
I need to send an http request over UART with basic authentification to 127.0.0.1:8888

{“values”:{},”states”:{“xxxxx”:2}}Q IIhh P GET /jsongen.html?PIN=XXXT&LNG=1&US=1&FN=getAttributes&ID=1-HMI HTTP/1.1
Authorization: Basic SlNP_________G1pbiE=
User-Agent: _____/2.1.0 (Linux; U; Android 6.0.2; Generic HMI Build/HMI20)
Host: 127.0.0.1:8888
Connection: Keep-Alive
Accept-Encoding: gzip

” hhC n@ HTTP/1.1 200 OK
Server: Climatix
Content-Type: text/html
Connection: close

any idea how to solve?

Thanks 🙂

By: PokskiMon

PokskiMon — Tue, 20 Jan 2026 09:22:45 +0000

In reply to Dr Quark. Have u tried going the other way? Making IO16 Tx and IO17 Rx??

By: Sara Santos

Sara Santos — Mon, 20 Oct 2025 13:37:18 +0000

In reply to Marc.

Yes.
You can do that.
At the moment, I don’t have any UART tutorials for the RPi.
Regards,
Sara

By: Marc

Marc — Mon, 20 Oct 2025 10:52:33 +0000

Can I connect UART-to-UART esp32 to Raspberry pi?

By: Dr Quark

Dr Quark — Sat, 15 Mar 2025 17:06:23 +0000

It turns out that the TFT_eSPI.h library (or something linked in that library) prevents the UART (or maybe just IO16) from functioning on receive (Rx). Transmit (Tx) works fine. You can check the CYD hardware by removing the tri-color LED and the port3 connections to the CH340 and connecting IO16 and IO17 directly to port3. Then just do a loop-back test by connecting IO16 to IO17.

By: Dr Quark

Dr Quark — Fri, 14 Mar 2025 20:05:52 +0000

I know IO4, IO16, and IO17 work because they are connected to the LED in the unmodified CYD. I can see in the o’scope the proper 0.2v-3.3v serial data stream on IO16. I setup and started UART(2) using:

HardwareSerial SerialPort(2) ;
setup() {
Serial.begin(9600) ;
SerialPort.begin(9600, SERIAL_8N1, 16, 17);
…
…

When I reset the CYD, I occasionally get one SerialPort.available(), then nothing further.

By: Dr Quark

Dr Quark — Fri, 14 Mar 2025 19:53:38 +0000

In reply to Dr Quark.

I know IO4, IO16, and IO17 work because they are connected to the LED in the unmodified CYD. I can see the proper 0.2v-3.3v serial data stream on IO16. I setup and started UART(2) using:

HardwareSerial SerialPort(2) ;
setup() {
Serial.begin(9600) ;
SerialPort.begin(9600, SERIAL_8N1, 16, 17);
…
…

When I reset the CYD, I occasionally get one SerialPort.available(), then nothing further.

By: Dr Quark

Dr Quark — Tue, 04 Mar 2025 18:59:34 +0000

I’m trying to get two CYDs talking on UART(2). I’ve removed the tri-color led and connected the P3 port directly to pins 16 and 17, with no pullup resistors. I’ve cross-connected pins 16/17 and I see good serial output from pin 17, but pin 16 never gives me a Serial2.available(). I’ve used both units on the Tx side and the Rx side, just to make sure they both work when sending and to see if maybe one of the Rx sides of the UART is bad. Nope, Tx works on both, but Rx doesn’t work either way.

Is there something odd about UART(2) on the CYD?