ESP8266 Community Forum

- Mon Jun 20, 2016 3:35 pm #49502 Hello, I am using the ESP8266 12E with arduino code, to read a thermistor with ADC. when I run connected to the USB the reading is correct. when I run on battery regulated 3.3V connected to the 3.3 pins, the reading on the ADC is lower. I noticed that connecting the Vin to 5V as well the reading is correct again. For all what I have read, my understanding is that the voltage used as reference for the ADC is the Vin. Question-- Can i connect the Vin to 3.3 as well to be properly used as reference? if this is the case... can I connect the USB as well without problems? if the Vin protected with a diode to prevent backfeeding from the USB to the 3.3 V? if this is not the case, will be easy to forget remove the jumper to 3.3 when going to connect the USB and fry the unit.

I would appreciate your help. I can make an sketch if necessary.
thanks

- Tue Jun 21, 2016 3:50 am #49530 Hi
I suggest to check the board layout. NodeMCU boards have external circuitry for the ADC port. This will give you an indication.
The ESP itself is always driven with 3.3V. 5V will kill it. Therefore even if you power the board via USB/5V, the Vcc Pins of the ESP will show 3.3V, since they are converted by a chip on the board of the NodeMCU.
Kind regards,
Urs.

- Tue Jun 21, 2016 2:29 pm #49556 The Nodemcu ESP8266 12E has a 5V input, that is where it get confused when used the ADC. if you use only the 3.3 v, the ADC reading is different than when use the 5V or USB. So my question is what is the correct way to wire the ADC on 3.3 and 5V