MQTT NodeMCU servo can react only on decimal array payload

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.

Looks like the motor is taking the position of the ASCII equivalent of the number when you send it as a string.

i.e.

• ASCII equivalent of the character '1' in 49 in decimal
• ASCII equivalent of the character '2' in 50 in decimal

Try sending the character 'a', the motor will go to 97.

If you want to send a string, you will have to change the following code:

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]'
}

to:

int location=String((char*)payload).toInt()
if((location>194)||(location<0))
  return;
myservo.write(location);