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By Istria
#81865 Hi people,

I have used the esp8266 is multiple projects before. Mostly the ESP-03 and a couple with ESP-12.
Until now I have always avoided using GPIO0, 2 and 15.

For my current project, I need more IO pins than before and am forced to use 2 out of the 3 mentioned GPIOs.
I chose GPIO 0 and 2, since they both have to be pulled high on boot, and my application needs pullup resistors on the transistor bases. GPIO15 needs a pulldown resistor at boot, so it's incompatible with my pullup needs.

The wiring is:
GPIO0-----330K RES-------2N2222A base.
same for GPIO2.

In my current setup I do NOT have external pullups yet. But the Wemos module has a fixed 10K pullup on GPIO0.

Problem after soldering the whole thing: It won't boot the program with GPIO0 and 2 connected. When I cut those 2 wires, it worked. But now i'm missing my 2 crucial outputs, so any idea what could be the case?

Thanks in advance!

User avatar
By AcmeUK
#81900 I need extra I/O for my wemo D1 mini, so I am going to use a I2C Bidirectional 16-Bit I/O Expander like this item:-
In the Arduino IDE I2C on an ESP8266 is simple; but do not forget to check if pull-ups are needed :)
User avatar
By btidey
#81904 330K into a transistor base should be fine as that won't load pull ups on GPIO0 and 2.

Have you tried checking the voltage on those 2 lines when reset is pulled low to check you are getting the high?

On a raw ESP-12F with no external pull ups I get about 2.8V with an effective internal pull up of around 36K.