ESP8266 Community Forum

When ESP8266 is powered up and determining boot mode 60ms according to the datasheet, what is the state of GPIO pins, other than GPIO0, GPIO15 and GPIO2. If I drive a relay would be turned ON momentarily and then initialized to OFF, I need to avoid startup jitter on the relays. essentialy I need to know before initiliazing the GPIOs they are at logic LOW, HIGH or floating.

Thanks and Best Regards

GPIO2/GPIO0 need to be pull-up at Reset to get into proper execute mode, while GPIO15 needs to be pulled-down.

I need to know before initiliazing the GPIOs they are at logic LOW, HIGH or floating.

GPIO4 and GPIO5 are floating and safe to use. All the rest are not. I will sometimes use GPIO15 to drive a relay (with a transistor) as it is low on start up. GPIO 12, 13, 14 all have weak pullups enabled on start. GPIO16 has a strong high.

GPIO12, 13, 14, and 16 can be used if you needed to but it is more of a pain. One way would be for the pin to drive a pnp transistor that would require a low to turn on, that would in turn the relay on. But since we are dealing with a 3 volt level then a npn transistor could then be used to drive a higher voltage relay. Yeah, all a pain in the ass. It just depends on what your needs are.

GPIO12, 13, 14 have a weak high and that can be negated with a low enough value resistor to ground and then you may be able to use a mosfet with a gate turn on voltage that is higher than a bipolar transistor's turn on voltage. Might be flaky unless you get the right components.

More complete details on the port pins can be found at https://www.mjt.me.uk/posts/esp8266-gpi ... and-reset/

If you need to drive more that 2 relays for which you can use GPIO4 and 5 (if free) I think is better to use a GPIO Port expander like the PCF8574 or similar. You have a way better control on it.

You can find a lot of related information's in the ESP8266 Analog extension board AN-1 series HERE and HERE. Also used it for my MPRSx8 Home automation board, more details HERE in the related article.

If you need even more, you can use 2 of them with different I2C address or the bigger brother PCF8575 - 16 GPIO lines, details HERE.

Happy breadboarding,
TJ.