I have the following circuit.

I connected vout with A0 pin(adc pin) of my esp8266. When I read the tension by a0(with command analogRead(A0)), I expect that value is about 667(0.652 V). But instead I get a random signal(not const)... by analogRead(A0) i get:
adc_value = 448
adc_value =0
adc_value =0
adc_value =1023
adc_value = 224
adc_value =0
adc_value =1023
etc...

I don't understand why...
PS: As a power supply I use a bench power supply and I already try to change esp8266 with another(to try if it if broken...)

 

hi dades.
Try connecting the 3.3V of the ESP to A0 input, you should read 1023.
Then try with A0 at 0V, should get 0000
Post your Sketch

E

@dades1988
BTW: I assume you have connected the 0V of the power supply to the 0V of the ESP.????

 

To ask the obvious question . . .
is the negative terminal of your supply (in the diagram) connected to the Vss of the ESP8266?

 

hi dades.
Try connecting the 3.3V of the ESP to A0 input, you should read 1023.
Then try with A0 at 0V, should get 0000
Post your Sketch

E

@dades1988
BTW: I assume you have connected the 0V of the power supply to the 0V of the ESP.????

View attachment 276729

No, I did not it. At the esp I only connected the a0 pin and the usb for the power supply. For you, do i need to connect it to ground of esp?

 

For you, do i need to connect it to ground of esp?

Hi dades,
Yes.
E

 

Hi dades,
Yes.
E

Now works!!
But now I don't understand why adc_value is about 160(0.15v). I should get adc_value equal about 667 (0.652 V) by:
Vout = vin *(r2 / (r1 + r2)) = 5 * 300 / (2000 + 300) = 0.65v

 

hi d,
Is the ESP a 12 Bit ADC ie: 4095.??? for 5V

E

 

I guess that the positive reference for the ADC is connected to 5V.
So that the reading would be
Vin/5V * 1024
which would read 133.

 

I bought this
NodeMCU ESP8266 ESP-12F

I think that range is 10bit. But I read about volt range is moved by 0-1v to 0-3.3v.
https://circuitsgeek.com/guides-and-how-to/esp8266-adc-tutorial-read-nodemcu-analog-input/

Actually, with adc_val / 1024 * 3.3 the result is correct.

 

The ESP8266 is a 10 bit ADC and uses a 3.3 volt V reference. Also the ESP8266 is non linear when measuring voltage especially levels below 1.0 volt. You can oversample, take many samples and average but keep in mind you can't make a silk purse from a sows ear. Some chips respond better than others.

To convert to reading voltage the code would look like this or similar:

const int analogInPin = A0;  // ESP8266 Analog Pin ADC0 = A0

int sensorValue = 0;  // value read from the pot
float volts;

void setup() {
  // initialize serial communication at 115200
  Serial.begin(115200);
}

void loop() {
  // read the analog in value
  sensorValue = analogRead(analogInPin);
 
 volts = (sensorValue * 3.3 / 1024);
  // print the readings in the Serial Monitor
  Serial.print("sensor = ");
  Serial.println(sensorValue);

  Serial.print ("Volts =  ");
  Serial.println (volts);
 
 
  delay(1000);
}

The result would look like this with 0.652 volts applied.


Note the standard voltage applied is 0.652 volts. You can see the low end error. Using your divider your output would be close to the above input.

Ron


Ron