ESP8266 Community Forum

- Sat Feb 13, 2016 8:36 pm #41074 I was thinking the Blue Led was on the ESP.....
On my ESP-13 If I apply 500 ohm to grd on gpio1(Rx) --> usb(Tx) the blue led on usb comes on..
my gpio2 is high / floating [not connected] appling 500 ohm shows nothing , which I expected....

The only way to turn on the Blue led with GPIO2 is 1) partial short 2) program error 3) Firmware issue
try reset unit , do not allow program to run, chk gpio1 / 2 level [ solid reset 470-gnd may force gpio1/2 hi ??]
Hopefully both will be hi --- apply 470 ohm gpio1 to gnd blue led on
--- apply 470 ohm gpio2 your led on [unless you are acting as source]

- Tue Feb 16, 2016 2:41 am #41204 TheBlue LED I'm referring to IS the one on the ESP (connected to TXD and flashes during serial data transfer).

This is my setup...

I'm programming the ESP-07 'conventionally' from an FTDI Friend (GPIO0 Low, Reset, return GPIO0 High and GPIO2 High then upload) - Once the ESP is programmed, reboot with GPIO0 High. The same process as for any ESP.

Then I plug the ESP into the breadboard, whereupon GPIO0 and GPIO2 are used as outputs - driving relays via optocoupler to +3.3V.

Whenever the second relay is triggered (GPIO2 Low), the blue LED on TXD is illuminated - and it's that which is confusing me.

There are Four pins between TXD and GPIO2 on the ESP (including RXD and GPIO0) so a short circuit is virtually impossible (and I've found nothing using a magnifying glass).

The uploaded code references only GPIO0 and GPIO2 as outputs when running (GPIO12 and GPIO13 are inputs) and serial communications (TXD/RXD) is not being used directly.

The only possible interaction that I can discover is in "Mode 4", where GPIO2 is used as a serial TXD for debugging purposes when the GPIO1/GPIO3 pair are used as a serial port for another device - but I've not been able to determine a) whether that would act on the inbuilt blue LED, b) how I might have invoked "Mode 4" or, c) how to get out of "Mode 4" if that is what's causing the problem.

It's not a disaster - everything works correctly - it's just very puzzling...