Calculation a height instead of printing centimeters

Questions » Calculation a height instead of printing centimeters

Christian Lind

9 years, 3 months ago.

Hey everyone.

I'm very new to the developer and IoT world, and this is probably a very simple question. Currently, when I print in CoolTerm, all i get is centimeters, and I would like the water height instead. How do I set up an equation, so I get the actual water-height? My container is 50 cm tall :) I hope you guys can help!

My code:

#include "mbed.h"
#include "SRF05.h"

AnalogIn fugtighed(p20);
SRF05 srf(p13, p14);
//DigitalOut diode(p10);
DigitalOut relay(p12);

Serial pc(USBTX, USBRX); // tx, rx
Serial WiFi(p28, p27); //WiFi serial
float moisture = 0.0;
float distance = 0.0;
//water_height = 50-distance
//water_volume = pi*r2*water_height
Ticker tick;
void ticker(){
    
    unsigned short moistureDigital = fugtighed.read_u16(); //0 - 65535
    moisture = ((float)moistureDigital)*(3300.0/65535.0); //0 - 3300mV
    pc.printf("moisture: digital: %d Analog(mV): %.2f\r\n", moistureDigital, moisture);
    
}

int main() {
    
    pc.baud(57600); //Setup BAUD rate to CoolTerm to 56700bps
    WiFi.baud(57600); //Setup BAUD rate to WiFi to 56700bps

    //tick.attach(&ticker, 1.0); //update every 1 sec

    
    //Print welcome message in CoolTerm
    pc.printf("\n* * * * * * * * *\nReady to send and receive!\n* * * * * * * * *\n\n\n");
    
    while(1) {
        
    unsigned short moistureDigital = fugtighed.read_u16(); //0 - 65535
    moisture = ((float)moistureDigital)*(3300.0/65535.0); //0 - 3300mV
    pc.printf("moisture: digital: %d Analog(mV): %.2f\r\n", moistureDigital, moisture);
    
    distance = srf.read();
        
        printf("Distance cm = %.1f\n", distance);              
         
         if (distance <= 50 && moisture >= 2000){
             
             //diode = 1;
             relay = 1;
             
        }else{
                 
              //diode = 0;   
              relay = 0;
              
        }
            
        WiFi.printf("LOOP8,3,moisture,%f,water_height,%f,water_volume,%f", moisture, distance, 11);
        wait(5);

//
    }
}

1 Answer

Andrea Corrado

9 years, 3 months ago.

Hey Christian :),

If understand this correctly, you have a container with an ultrasonic attached to the top of it? And you want to know how much water is in the container. There are two ways of doing this.

1. Physically measure yourself the distance from the front of the ultrasonic sensor to the bottom of inside the container lets call it zero_measurement. Then the the water_height= zero_measurement - distance.

2. You could automatically measure the distance with ultrasonic sensor every tie the platform turns on, first take a measurement when there is nothing in the container, this again is a zero_measurement, just now it is dynamic to the container.

Let me know if that helps.

Best Regards,

Andrea, team mbed

Christian Lind

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9 years, 3 months ago.