[Solved] Measuring AC current with ESP8266 and ACS712, calculation

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@fregger I want to do exactly the same thing, but I’m failing to understand your final wiring.

The ESP8266 is only able to read 0-1V at the A0 pin (analog), so at zero amps (no load) you should be getting 1024 already, since the ACS outputs 2.5V at 0 amps. Don’t understand how you are getting ~512

Could you please post the final schematics? I’m also new with electronics.

My multimeter reads the expected 2.5V at zero amps on the acs712.

He uses a voltage divider (10k-Poti)
One end to the sensor, the other to ground. The middle one to A0.
At 0 Amps you trim the Poti till you get 0.5V (or 512 at the esp)

And here’s the sketch, just fill out the wifi credentials and the mqtt server’s ip-nr. I did not define mqtt-server username and password. Works like a charm

 * Modified for wifi and mqtt
Measuring AC Current Using ACS712 20A Module
www.circuits4you.com
*/

#include <ESP8266WiFi.h>
#include <PubSubClient.h>

#define wifi_ssid "YOUR_SSID"
#define wifi_password "YOUR_WIFI_PASSWORD"

#define mqtt_server "IP_NR_MQTT_SERVER"
#define mqtt_user "your_username"
#define mqtt_password "your_password"

#define solaramps_topic "solar/amps"

const int sensorIn = A0;
int mVperAmp = 100; // use 100 for 20A Module and 66 for 30A Module and 185 for 5A Module

double Voltage = 0;
double VRMS = 0;
double AmpsRMS = 0;

WiFiClient espClient;
PubSubClient client(espClient);

void setup(){
 Serial.begin(9600);
 setup_wifi();
 client.setServer(mqtt_server, 1883);
}

void setup_wifi() {
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(wifi_ssid);

  WiFi.begin(wifi_ssid, wifi_password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    // If you do not want to use a username and password, change next line to
       if (client.connect("ESP8266Client")) {
    // if (client.connect("ESP8266Client", mqtt_user, mqtt_password)) {
      Serial.println("connected");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void loop(){
 if (!client.connected()) {
    reconnect();
  }
 client.loop();

 Voltage = getVPP();
 VRMS = (Voltage/2.0) *0.707;  //root 2 is 0.707
 AmpsRMS = (VRMS * 1000)/mVperAmp;
 Serial.print(AmpsRMS);
 Serial.println(" Amps RMS");
 client.publish(solaramps_topic, String(AmpsRMS).c_str(), true);
}

float getVPP()
{
  float result;
  int readValue;             //value read from the sensor
  int maxValue = 0;          // store max value here
  int minValue = 1024;          // store min value here

   uint32_t start_time = millis();
   while((millis()-start_time) < 1000) //sample for 1 Sec
   {
       readValue = analogRead(sensorIn);
       // see if you have a new maxValue
       if (readValue > maxValue)
       {
           /*record the maximum sensor value*/
           maxValue = readValue;
       }
       if (readValue < minValue)
       {
           /*record the minimum sensor value*/
           minValue = readValue;
       }
   }

   // Subtract min from max
   result = ((maxValue - minValue) * 5.0)/1024.0;

   return result;
 }```

Thanks. I’ll buy a couple and test that.

But don´t buy “normal” Potis, you need the trimmer-type