ESP8266 Community Forum

- Sat Aug 08, 2015 6:01 pm #25390 I strongly agree with Squonk !

Having almost 35 years of electronical/software engineering experience, I'm usually voting for safe bet.
But in case of ESPs, my experience changed a lot, I'm now even playing strong safety !

Let's just imaginate an ESP devices in the fields with harsh environment which his doing deep-sleep for a certain amount of time, and then it wake-up exactly at the moment when ESD is stronger than the weak internal pullups and driving the GPIO0 or GPIO2 to a level equivalent to LOW (yes, ESD is AC, so it can act an LOW or as HIGH depending of it waves), the ESP will simply wake-up in a bad mode, device been stucked there forever until you recycle the power to make it run again.

Now, why having those external pullups even if there are some internal ones ? Simply because those internal ones are too weak ! Maybe Expressif should have choosen stronger ones.
Just to prove that, their document 0B-ESP8266__Hardware_User_Guide__EN_v1.1.pdf (http://bbs.espressif.com/download/file.php?id=562) has a contradiction (which seems to admit the above facts) :
In the Section "2.2.2 Power-on Sequence and Power Reset", they mentioned "There is an internal pull-up in the CHIP_EN pin, so no external pull-up is needed." and few lines later "If voltage for CH_EN pin is low, the chipset ESP8266EX will power off. Note that this pin cannot be dangled.".

So, this means they admit that an external strong pullup is NOT superfluous ...

Also, in the same section, they mentioned "There exists internal pull-up resistor in the reset pin, Pin32, which can be left dangled when it is not used. When the chip is enabled, the reset pin is held low. In order to avoid reset caused by external interference, the lead is generally required to be short, and no external pull-up resistor is necessary.".
We all remember that many people on the forum have posted thread about this reset issue due to "antenna effect", but here, in this case, Espressif never updated their specs specifying not to leave the pin dangled, but maybe they will in the future.

All this is true with ANY critical pins, even if GPIO0/GPIO2 is read only during few nanoseconds, the "antenna" effect still can lead to improper state.

The conclusion is that I've always said that since the beginning, member "Cal" stated more than 6 weeks ago that I was right because he understand what is the "antenna" effect, and I'm pretty sure there are several other members who already agree but they did not given their voice yet here.

- Sun Aug 09, 2015 3:09 am #25418 You can keep this going till you are blue in the face . The fact is despite"anybody's strong recommendations " GPIO2 can be and is often left floating .

You may assert whatever you like, but I have shown in previous posts and in practice that it is not needed to take it high. Do so if you wish, or, if you succumb to posts such as these above, but my statement is correct . The assertion that it must be taken high is wrong.

Get you modules here:

https://www.banggood.com/custlink/KvGGhGF4wG

- Sun Aug 09, 2015 10:12 pm #25494

- Wed Aug 12, 2015 1:39 am #25758

You can keep this going till you are blue in the face . The fact is despite"anybody's strong recommendations " GPIO2 can be and is often left floating .

Please calm down! I don't know you and you apparently don't know me, but you are aggressive. I am not "anybody", using this word is pejorative, at least in my native language.

You may assert whatever you like, but I have shown in previous posts and in practice that it is not needed to take it high. Do so if you wish, or, if you succumb to posts such as these above, but my statement is correct . The assertion that it must be taken high is wrong.

I browsed your previous posts and don't see such a demonstration, only statements that it works OK for you. This is not necessarily the case for others.

I have already installed devices in mountainous areas where thunderstorms are commonplace, or played with an ESD gun for certification purposes, and this is why I strongly recommend adding external pullup resistors, instead of relying on weak internal pullups.

Espressif themselves now lowered the value of the resistor on nRESET to 5k because of problem with the chip not resetting cleanly. As I said above, all major ESP8266 dev boards are also using external resistors, for a good reason.

Your statement that the GPIO2 pin can be left unconnected is correct indeed, but recommending this practice against advises from several experienced electronic engineers saying it is safer to add an external pullup resistor to prevent the chip from booting into a deadlock is not responsible.

Going back to the OP, I strongly suspect a problem with the power supply, only working when the UART adapter is connected because of the increased available current. What power supply did you use?