Keep on getting -1 as a reading when trying to send info from an SR04 sensor to thingspeak

Cloud
1

so i am having trouble with the ultra sonic sensor SR04 because when i try to send thingspeak data it only gets -1. im not sure why so here is my code:

// This #include statement was automatically added by the Particle IDE.
#include "HC_SR04/HC_SR04.h"

int distance = 0;

int cm;

int trigPin = D2;
int echoPin = D6;


HC_SR04 rangefinder = HC_SR04(trigPin, echoPin);

void setup() 
{
}

void loop() 
{
    distance = rangefinder.getDistanceCM();
   cm = distance;
    Particle.publish("ultra_sensor_test", String(cm), 60, PRIVATE);
    delay(6000);
}

im not sure why i keep getting -1 as reading. i have the wiring correct and the ultra sonic sensor works fine. if anyone could help that would be great. thank you.

2

For some reasion this condition evaluates to true

  if (distance < _minCM || distance > _maxCM){
   return -1;
  }

where these are the limits

  _minCM = 10.0;
  _maxCM = 250.0;
3

As ScruffR pointed out, make sure you are taking measurement within the Default Range of 10cm to 250 cm.

I believe You can also change this range with the following line before Setup()

HC_SR04 rangefinder = HC_SR04(trigPin, echoPin, 5.0, 500.0);

I found (and use) code for my JSN SR04 that doesn’t use a Library. It performs great, but the actual minimum distance I can reliability measure is 11 inches with this sensor. Let me know if you want to try it.