In my Vacuum Cleaner project I use 6 HC-SR04 ultrasonic sensors, motor shield and Arduino Uno. The sensors usually measure correct distances but sometimes they mesure completely fail. It looks like this in Serial Monitor:
It makes that robot behaves weird. Where fail comes from?
In order to reduce impact of this I measure distance from every of 6 sensors three times and calculate average distance of it, but it solves the problem just a little.
Here is how I calculate distances:
for (j = 0; j < 3; j = j + 1) {
for (i = 0; i < 6; i = i + 1) {
delayMicroseconds(5);
digitalWrite(ultrasonic[i], HIGH); // triggering of a high pulse on sensor i
inMode(ultrasonic[i], OUTPUT); // pin of sensor i becomes an output
digitalWrite(ultrasonic[i], LOW); // clearing of output i
delayMicroseconds(10);
digitalWrite(ultrasonic[i], LOW); // turning off a high pulse on sensor i
pinMode(ultrasonic[i], INPUT); // pin of sensor i becomes an input
imp_back[i][j] = pulseIn(ultrasonic[i], HIGH); // measuring of a come back time of high pulse to sensor i
distance[i][j] = imp_back[i][j]*0.0344/2; // calculation of a distance to an obstacle in front of sensor i in cm
delayMicroseconds(10);
}
}
for (i = 0; i < 6; i = i + 1) {
avr_distance[i] = (distance[i][0] + distance[i][1] + distance[i][2])/3;
}
Do you have any ideas where fail comes from and how to eliminate it?
imp_back[i][j] = pulseIn(ultrasonic[i], HIGH); // measuring of a come back time of high pulse to sensor i
distance[i][j] = imp_back[i][j]*0.0344/2; // calculation of a distance to an obstacle in front of sensor i in cm
It's silly to keep a 2D array of times, when all you care about is the distance.
You don't even care about the individual distances - just the average distance. So that array is unnecessary, to.
Getting the distance from a PING sensor should be done in a function, NOT as part of loop().
Pass the function the pin number and the number of times to ping, and have it return hte average.
Thank you for all answears. I checked all suggestions.
NewPing's median method. It eliminates almost all error readings. Disadvantage with this is that it take a lot of time to do measurements. For instance I have 6 ultrasonic sensors in my robot and if I measure 5 times for each sensor, takes it 0,7 second. It is to long in my project but good to know that it exists this kind of function.
Slowing down pinging. I tried to slow down and take measurements even every 100 microseconds each, but it doesn't give noticeable results..
I used a function from NewPing library to measure distances. I received less errors.
Most of errors comes when robot measures distance to a mirror when drives on the floor. On a table goes it quite well, but it will be vacuum cleaner so it will work mostly on the floor with all kinds of obstacles. I made a movie earlier about how the robot plays with the ball with 6 ultrasonic sensors: Obstacle Avoiding Robot. Object Following Robot. Arduino Project 2018. Part 2. - YouTube.
One of the things, I have done, to quiet down the SR04's is to put a .47uF capacitor across the V+ and Gnd pins on the front of the sensors, between the R/T transducers.
I am using 2 sensor pairs. Rt and Rb as one sensor pair and Lt and Lb as another sensor pair. Rt is fired and if it gets a reflection, a non zero value, Rb is fired. Rt and Rb are compared and, for my application, if Rt=Rb then object detected. The same goes for Lt/Lb pair.
I have mounted Rt and Rb with Rb on the bottom and Rt on top of Rb, I found that the top / bottom mounting to gave less noise or false readings.
