Hi everyone,
this is my first post here, but I’ll try my best.
I searched for the answer in existing topics but with no success … so here’s my problem:
I’d like to code an object class to handle my ultrasound HY-SRF05 sensor on Arduino Nano v3. The sensor connection and reading the values works allright. I tried to implement a smoothing approach posted here https://www.arduino.cc/en/Tutorial/BuiltInExamples/Smoothing but I wanted to be “classy” and code a more general object class that I could later use for other projects.
When I open the Serial plotter I can see a working noisy signal from the ultrasound but the smoothed/averaged value is mathematicly incorrect on the first glance. I’m not a C programmer so I sniff the problem there 
class Ultrasound {
byte trigPin; // ultrasound trigger pin
byte echoPin; // ultrasound echo pin
long interval; // intervall between readings in millis
short unsigned avgNum; // number of readings in running average
long unsigned prevMillis; // time of previous reading
float value;
float average;
int *readings; // the readings set for the running average
float sum;
public:
Ultrasound(int tPin, int ePin, long interv, int aNum = 10) {
trigPin = tPin;
echoPin = ePin;
interval = interv;
avgNum = aNum;
initReadings(aNum);
}
float getValue() {
return(value);
}
float getAverage() {
return(average);
}
// I'd like to be able to change the reading interval during runtime
void setReadingInterval(long interv) {
interval = interv;
}
// I'd like to be able to change the averaging number during runtime
void setAverageRange(int num) {
avgNum = num;
initReadings(num);
}
void setup() {
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}
void loop() {
short unsigned readIndex = 0;
long unsigned curMillis = millis();
if (curMillis - prevMillis >= interval) {
value = readValue();
prevMillis = curMillis;
// subtract the last reading:
sum = sum - readings[readIndex];
// read from the sensor:
readings[readIndex] = value;
// add the reading to the total:
sum = sum + value;
// advance to the next position in the array:
readIndex = readIndex + 1;
// if we're at the end of the array...
if (readIndex >= avgNum) {
// ... jump back to the beginning:
readIndex = 0;
}
// calculate the average:
average = sum / avgNum;
}
}
private:
float readValue(byte lowTime = 2, byte highTime = 5) {
long response;
digitalWrite(trigPin, LOW);
delayMicroseconds(lowTime);
digitalWrite(trigPin, HIGH);
delayMicroseconds(highTime);
digitalWrite(trigPin, LOW);
// get the ultrasound response
response = pulseIn(echoPin, HIGH);
// calculate the distance in cm
return(response/58.31);
}
// needed to initialize the readings list which has unknown length at compile time
void initReadings(int num) {
// initialize all the readings to 0:
readings[num] = {0};
}
};
// trigger and echo pins for the ultrasound sensor
const byte pTrig = 4;
const byte pEcho = 5;
// construct the object instance
Ultrasound us(pTrig, pEcho, 10, 1000);
void setup() {
us.setup();
// start serial communication
Serial.begin(9600);
}
void loop()
{
us.loop();
Serial.print(us.getValue());
Serial.print(" ");
Serial.print(us.getAverage());
Serial.println(" ");
}
I will be very glad for any suggestions.
Cheers!