MQTT NodeMCU servo can react only on decimal array payload

Configuration
1

I’m creating a fish feeder with SG90 servo and NodeMCU

I used this sketch:

```
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <Servo.h>
// Update these with values suitable for your network.
const char* ssid = "your_wifi_hotspot";
const char* password = "your_wifi_password";
 const char* mqtt_server = "broker.mqttdashboard.com";
//const char* mqtt_server = "iot.eclipse.org";

Servo myservo;  // create servo object to control a servo
WiFiClient espClient;
PubSubClient client(espClient);

void setup_wifi() {
   delay(100);
  // We start by connecting to a WiFi network
    Serial.print("Connecting to ");
    Serial.println(ssid);
    WiFi.begin(ssid, password);
    while (WiFi.status() != WL_CONNECTED) 
    {
      delay(500);
      Serial.print(".");
    }
  randomSeed(micros());
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char* topic, byte* payload, unsigned int length) 
{
  Serial.print("Command from MQTT broker is : [");
  Serial.print(topic);
  for(int i=0;i<length;i++)
  {
    if((int)payload[i]>194||(int)payload[i]<0)
    break;
    myservo.write((int)payload[i]);              // tell servo to go to position in variable '(int)payload[i]'
  }
}//end callback

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) 
  {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    //if you MQTT broker has clientID,username and password
    //please change following line to    if (client.connect(clientId,userName,passWord))
    if (client.connect(clientId.c_str()))
    {
      Serial.println("connected");
     //once connected to MQTT broker, subscribe command if any
      client.subscribe("OsoyooCommand");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 6 seconds before retrying
      delay(6000);
    }
  }
} //end reconnect()

void setup() {
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
  myservo.attach(D1);  // attaches the servo on pin D1 to the servo object
}

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

}
```

The servo is working when I use MQTTBox in order to send a payload as “Decimal Array”, it is however is giving me a hard time when I send payload as JSON string.

If I send “Decimal Array” 1 it does turn Servo to position 1, however if I simply send 1 as a payload as a string it moves Servo to position 49. If I send payload as 2 it moves to position 50. If I send payload as 10 then position is 4948 looks like position of 1 and position of 0 at the same time.

My ultimate goal is to send those payloads via HomeAssistant which are sent as string or JSON, however I don’t find a correct solution at the moment. I would highly appreciate any help or solution.

2

JSON is always sent as a string. The ascii code for “1” is 49.

3

Thank you @gpbenton, my goal if to turn servo from 180 to 0 and then again to 180. I’m still not sure how I could form my MQTT payload in Home Assistant in order to do so.

I found this converter: https://www.browserling.com/tools/text-to-ascii,and this https://www.browserling.com/tools/ascii-to-text but none of the values give correct result.

4

If you do the conversion from string to integer in your sketch, you just send the value you want from home assistant.

5

Hi, I feel that I could be closer to the solution, but still not there.

added this:

  i=Serial.parseInt();

with the hope that it will change string to integer, unfortunately it didn’t really help.

I used it here:

void callback(char* topic, byte* payload, unsigned int length) 
{
  Serial.print("Command from MQTT broker is : [");
  Serial.print(topic);
  Serial.print(" Rotation angle is:");
  Serial.print("   ");
 // for(int i=0;i<length;i++)
  {

//    if((int)payload[i]>194||(int)payload[i]<0)
  //  break;
  i=Serial.parseInt(); // Added this code to change variable to integer
    myservo.write((int)payload[i]);// tell servo to go to position in variable '(int)payload[i]'
    Serial.print((int)payload[i]);//print the rotation angle
    Serial.print("]");
    Serial.println();
  }
}//end callback
6

I fail to see how this would change the payload to an integer. You’re not using Serial.

Seems to me this should be
myservo.write(int(payload[i]));

7

@flamingm0e, your last suggestion is not returning any errors but I was not able to use string servo would move to 48 if I publish 0
and
495648 if I publish 180

So I’m still not sure how to convert string that I will be sending from Home Assistant and control servo.

8

You would probably need to convert all your code to use int() properly if you want it to work. I’ve never seen it written as (int)payload[i]. I’ve always used and seen it as int(payload[i])

9

Hi all, thank you for your response and help, I did manage to solve the problem.

I changed my sketch to this one:

It already accepts all strings.

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