How to add a formula

[mutidave]

Hello everyone,
I’m working with my photon and a potentiometer. And I managed to measure the voltage and publish it online, but I want to do something with the measured voltage. For example, I want a formula like (voltage*0,01 =) and I’ve already searched on docs.particle.io, but I can’t find it.
Can someone help me out? Thanks in advance,

This is my code for now

const String topic = "Potentio";

//this enables Serial communication. When TRUE the Spark will send the measurement value over
//the USB serial every "intervalSerial" seconds. Only change to FALSE when no further debugging
//is needed
#define DEBUG_SERIAL TRUE 

//Sensor is connected to this pin.
const int inPin = A0; 

//number of seconds between uploads to the Spark Cloud. This may never be lower than 60
//because IFTTT does not allow for more triggers than 1 per minute.
const int intervalOnline = 5; 

//number of seconds between uploads over the USB serial
const int intervalSerial = 1; 

//number of milliseconds between measurements. This could be as low as needed, but higher values
//results in a more stable behaviour of the ADC. 
const int intervalMeasurement = 100;

int measurement;

void setup(){
    
    //start Serial communication
    if (DEBUG_SERIAL) Serial.begin(9600);

    //set the inPin to INPUT
    pinMode(inPin,INPUT);
}

void loop(){
    
    //get timestamp
    int t=millis();

    //every intervalMeasurement milliseconds, do a measurement 
    if (t%(intervalMeasurement)<1){
        measurement = analogRead(inPin);
        delay(1);
    }

    //every intervalSerial seconds, send measurement over Serial USB
    if (DEBUG_SERIAL){
        if (t%(intervalSerial*1000)<5){
            Serial.println(measurement);
            delay(5);
        }
    }
    
    //every intervalOnline seconds, publish measurement to Spark Cloud
    if (t%(intervalOnline*1000)<10){
        String measurementText = String(measurement, DEC);
        Spark.publish(topic,measurementText);
        delay(10);
    }
    

}

[ScruffR]

When you already have the voltag reating in a variable, just apply whatever calculation you want to that variable and store the result into a new variable or store it back in the original

double voltage = 123.4;
double result;

result = voltage * 0.1; // calculate and store in other variable
// or 
voltage *= 0.1; // this is the same as voltage = voltage * 0.1;

[mutidave]

But how do I store the voltage in a variable? Could you perhaps add a calculation in my code?

[Moors7]

But how do I store the voltage in a variable?

Like you would with any other variable? You’ve even done so in your code, repeatedly:

int t=millis(); //assigns the millis() value to a new variable 't'

measurement = analogRead(inPin); // assigns the analog value from inPin to a variable 'measurement'

Could you perhaps add a calculation in my code?

You already have a couple of calculations in your original code…

if (t%(intervalOnline*1000)<10){
  // ...
}

That will multiply the intervalOnline value with 1000. That is then used with a modulo operation on t and checked if the result is smaller than 10.

[mutidave]

But how exactly can I multiply the value that is published online by 4. What exactly do I need to add in the code?

[Moors7]

That will multiply the intervalOnline value with 1000

I wonder what’d happen if you swapped that ‘1000’ for another value… Say… 4?

All the information you’re asking for is already implemented in your original code. How exactly did you come up with that ;)?

[Muskie]

You can multiply by four prior to publishing like so:

//every intervalOnline seconds, publish measurement to Spark Cloud
if (t%(intervalOnline*1000)<10){
String measurementText = String(measurement * 4, DEC);
Spark.publish(topic,measurementText);
delay(10);
}

However, you can’t change the value once you have published, if that is what you are asking.

[mutidave]

Thanks a lot, problem solved;)

[mutidave]

Thanks a lot, you really saved me here;)

[mutidave]

btw, do you perhaps know how I can add the word “degrees” so I will read my measured values online like "value degrees"

[Moors7]

This tutorial might be interesting:

Tutorial: Getting Started with Spark.publish()

Here’s a tutorial to get you started using Spark.publish(). Let’s imagine you want to monitor your core’s uptime, that is, how many hours, minutes, and seconds since the last time the core was reset or powered-up and view it on a web page that you can leave open all the time. You can use the millis() function to measure time and for this example, you can ignore the fact that it can wrap-around back to zero after many days. So you need two things, code for your Spark core and code for a web page…

[BulldogLowell]

Or just read the docs
String Class

[Muskie]

//every intervalOnline seconds, publish measurement to Spark Cloud
    if (t%(intervalOnline*1000)<10){
        String measurementText = String(measurement * 4, DEC) + " degrees";
        Spark.publish(topic,measurementText);
        delay(10);
    }

Strings can be added (concatenated) using the addition operator.

[mutidave]

thanks;)