No serial output from ESP8266, but TX LED still flashes?

Trying to debug a sketch for a H801 LED controller, which is basically an ESP8266 with some power transistors. It has the TX, RX, VCC and GND pins exposed, as well as GPIO 0 for flashing firmware, and seems to behave no different to a standard ESP8266.

For some reason, I cannot get anything to show up on the serial monitor. I've done the basic stuff like checking the baud rate's the same (and changing it to 9600 doesn't help), making sure the correct COM port is selected, etc. but even just using a basic test script like the one below, absolutely nothing shows up in the serial monitor at all.

void setup() {
  // put your setup code here, to run once:
  Serial.println("Hello, you've entered setup()...");

void loop() {
  // put your main code here, to run repeatedly:
  Serial.print("Test 1()...");
  Serial.println("Test 2()...");
  Serial.println("Test 3()...");

When running the above code, the TX light on the H801 blinks like you would expect, but the RX light on my FT232 serial adapter doesn't. I thought it could be a connection issue, but I have no problem flashing firmware to the ESP and both the TX and RX LEDs light up like normal while flashing. I've tried this with three different H801s, so it's not a hardware issue, and from what I can tell other people have been able to use the serial monitor on these things with no problem. I also ran the above script on a Pro Mini using the same serial adapter and it worked fine, so I don't believe the adapter is at fault.

Does anyone know what else I could try to narrow down the problem? Or some way apart from serial to debug my other script? I found a library called RemoteDebug which is suppose to let you debug wirelessly using Telnet, but I couldn't get it to work for some reason. Thanks!

Is the ESP8266 running a NoNOS AT firmware?

Try sending this


You should get an OK response

I’m not sure if there’s a way to check the firmware that doesn’t require a serial port, but the one that’s been selected in the Tools menu is nonos-sdk 2.2.1+100. I was going to upgrade it, but it seems like I would need access to pins that don’t have headers (but I might be wrong, there seem to be a lot of conflicting tutorials). Oddly, I can use esptool to read the firmware (I’ve attached it, in case that helps), although it doesn’t tell me what version it is.

I tried the command, still nothing. When I press “send” in the serial monitor, the TX light on the USB adapter flashes, but the TX light on the H801 does not, indicating that it didn’t send a response. I can’t tell if the ESP is receiving the command or not, as I don’t think the H801 has an RX light. (226 KB)