ESP8266 Community Forum

- Tue Oct 25, 2016 12:14 pm #57096 Hello, please see me post on stackoverflow. I have problems to read from Serial port on ESP01, if Arduino and ESP01 are powered from external power source.

http://arduino.stackexchange.com/questions/30386/esp01-connected-to-arduino-cant-publish-mqtt

- Tue Oct 25, 2016 12:33 pm #57098 As mentioned in responses, Arduino UNO is NOT able to provide more than 50mA on 3.3V pin !

The fact that it is working on most of USB-TTL is that those one can deliver more than 300mA.

So, you should use the same 5V of the Arduino, add a 3.3V regulator along with big capacitor such 100uF or even 220uF attached nearby the ESP VCC pins.

- Tue Oct 25, 2016 12:51 pm #57100

As mentioned in responses, Arduino UNO is NOT able to provide more than 50mA on 3.3V pin !

The fact that it is working on most of USB-TTL is that those one can deliver more than 300mA.

So, you should use the same 5V of the Arduino, add a 3.3V regulator along with big capacitor such 100uF or even 220uF attached nearby the ESP VCC pins.

Thank you for your post.

I am still litle bit confused in this case. If I understand correctly, If I connect Arduino with my desktop via USB, then 3.3 V pin of Arduino can deliver 300mA.

When I disconnect USB and use external power supply 12V/1A (connected to Arduino power connector) then pin 3.3 V can deliver max 50mA? It does not make sence for me. I would expect same current limitation regardless on power input..

Please can you explain?

- Tue Oct 25, 2016 2:09 pm #57106 No, the Arduino NEVER provide more than 50mA in any case. The LP2985 regulator is not strong enough.
(EDIT : in fact, I've just verified : the TI LP2985 regulator is rated 150mA. Maybe other manufacturers of LP2985 are limited to 50mA instead, that is why most people said 50mA)
If you use Arduino as USB-TTL and connect to this 50mA 3.3V, you are lucky if it works, even for uploading firmware.
But as soon WiFi radio is starting, for sure it won't work. Many people complain about that.
I've never try it myself, since I've always used external PSU, or direct USB connection of modules such Wemos-D1-Mini.