ESP8266 Community Forum

- Sun Apr 10, 2016 9:32 pm #45263 I'm trying to use the GPIO00 and 02 as an output, but, on start up, they're linked in a circuit with a transistor that triggers a 5v relay.

The problem is, when the esp8266 is starting, the GPIO's are linked in base pin of the transistor, and so, doesn't run the firmware, doesn't start the logic inside him.

I googled, i searched here in this forum, but, nothing that i read, helped me to resolve this question.

I know that i can use the I2C to expand the IO's, but, i don't want.

What can i do about this?

Sorry about my poor english.

Regards.

J Moura.

- Mon Apr 11, 2016 7:56 am #45277 Your searches were not thoroughly done, because there are plenty of questions/answers about this subject.

First, lets explain GPIO behaviour when used as output :

viewtopic.php?f=13&t=7741&p=39319&hilit=source+sink#p39319
viewtopic.php?f=6&t=7412&p=37706&hilit=source+sink#p37696

Now, since you are using a transistor to drive the relay :

viewtopic.php?f=13&t=9441&p=45219&hilit=MPSA13#p45219

In conclusion, the GPIO idle state should always be the same level as the require Boot state.
Since both GPIO2/GPIO0 need to be HIGH for proper boot, your relay circuit need to be HIGH when relay is OFF, so as explain in the last link, you need 2 NPN transistors, the first one to invert the GPIO level, and the second to drive the current to the relay. Those NPN can also be replaced by MOSFETs.

- Fri Jun 02, 2017 5:09 am #66632 thanks martin for useful information...I'm facing the same problem with GPIO 0, 15, 10 & 16 i mean realys trun on for almost 1 second while reset. how can i solve this problem for GPIO10 & 16. by the way i'm using ULN2003 to trigger 12v relays.

thanks in advance,