Robin2:
That sounds interesting. I can imagine that other people might find other uses for the idea.
Can you tell us more about your final project?
What sort of gestures can it distinguish?
Maybe you could provide a diagram that illustrates how it looks and how it is used?
...R
Cerainly! 
I already have it's fritzing diagram here;
It can recognise an "up" swipe and a "down" swipe from approx. 150cm but the maximum for hc-sr04 is way higher up to 400cm which is not neede in my case. I am using this to control a window blind set which works with a remote controller on a motor. A type of step motor but works much differently from common types
And the code I used is here;
#include <neotimer.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>
#include <NewPing.h>
#define SONAR_NUM 2 // Number or sensors.
#define MAX_DISTANCE 90// Max distance in cm.
#define PING_INTERVAL 33 // Milliseconds between pings.
#define ledUp 12
#define ledDown 7
unsigned long pingTimer[SONAR_NUM]; // When each pings.
unsigned int cm[SONAR_NUM]; // Store ping distances.
uint8_t currentSensor = 0; // Which sensor is active.
uint8_t lastSensor = 0; // Which sensor is active.
int value1;
int value2;
LiquidCrystal_I2C lcd(0x27,2,1,0,4,5,6,7); // 0x27 is the I2C bus address for an unmodified module
Neotimer thetimer = Neotimer(1000);
NewPing sonar[SONAR_NUM] = { // Sensor object array.
NewPing(9, 10, MAX_DISTANCE),
NewPing(11, 8, MAX_DISTANCE),
};
void setup() {
pinMode(ledUp, OUTPUT);
pinMode(ledDown, OUTPUT);
digitalWrite(ledUp, HIGH);
digitalWrite(ledDown, HIGH);
Serial.begin(115200);
lcd.setBacklightPin(3,POSITIVE);
lcd.setBacklight(LOW);
lcd.begin(16, 2);
lcd.clear();
pingTimer[0] = millis() + 75; // First ping start in ms.
thetimer.start();
for (uint8_t i = 1; i < SONAR_NUM; i++)
pingTimer[i] = pingTimer[i - 1] + PING_INTERVAL;
}
void loop() {
for (uint8_t i = 0; i < SONAR_NUM; i++) {
if (millis() >= pingTimer[i]) {
pingTimer[i] += PING_INTERVAL * SONAR_NUM;
if (i == 0 && currentSensor == SONAR_NUM - 1)
sonar[currentSensor].timer_stop();
currentSensor = i;
cm[currentSensor] = 0;
sonar[currentSensor].ping_timer(echoCheck);
}
}
if(thetimer.repeat(300)){
lcd.setCursor(0,1);
lcd.print("Reset");
value1 = 0;
value2 = 0;
}
lcd.setCursor(0,0);
lcd.print("Working");
lcd.setCursor(0,1);
lcd.print("No Action");
if(cm[0] > 0 || cm[1] > 0)
{
Serial.print("0");
Serial.print("=");
Serial.print(cm[0]);
Serial.print("cm ");
Serial.print("1");
Serial.print("=");
Serial.print(cm[1]);
Serial.print("cm ");
Serial.println();
}
if (cm[0] > 10){
value1 = 1;
thetimer.reset();
delay(50);
}
if (cm[1] > 10 && value1 == 1){
value1 = 0;
goUp();
digitalWrite(ledUp, LOW);
delay(400);
digitalWrite(ledUp, HIGH);
lcd.clear();
value1 = 0;
value2 = 0;
}
//set value 2 true
if (cm[1] > 10){
value2 = 1;
thetimer.reset();
delay(50);
}
if (cm[0] > 10 && value2 == 1){
value2 = 0;
goDown();
digitalWrite(ledDown, LOW);
delay(400);
digitalWrite(ledDown, HIGH);
lcd.clear();
value1 = 0;
value2 = 0;
}
}
void goUp()
{
Serial.println("MovingUpStarted");
lcd.setCursor(0,1);
lcd.print("Go Up Trigger");
value1 = 0;
value2 = 0;
}
void goDown()
{
Serial.println("MovingDownStarted");
lcd.setCursor(0,1);
lcd.print("Go Down Trigger");
value1 = 0;
value2 = 0;
}
void echoCheck() { // If ping echo, set distance to array.
if (sonar[currentSensor].check_timer())
cm[currentSensor] = sonar[currentSensor].ping_result / US_ROUNDTRIP_CM;
}