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Author Topic: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5  (Read 113306 times)
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Hi Tim,

In the end I brought some Yourdunino SRF06's. They are accurate at their distance measurements but unfortunately their distance max's out at about 200cm, beyond that they return 0's. I was looking for something which would hopefully be accurate to about 350cm.... I have gone ahead and bought a few of Maxbotix XL EZ0 sensors. Do you think that I could modify your New Ping code to work with these sensors or would I need to start from scratch?

Did you set the maximum distance to higher than 200cm?  Mine work well to easily over 400cm.  Maybe it's the size of the object or how sonically reflective it is?  Try using a wall as your maximum distance measurements, that's what the distance specs use.

Tim
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Yes, I set the maximum distance at 300 but then the sensors return 0's. All the sensors are pointing at a solid wall 250cm away, but the sensors are returning 0's rather than seeing the wall, thus I'm assuming out of their range. I thought it strange as the Hr04's measured/worked fine over this distance. I've tried different delay times to see if there is any interference, up to 100ms but it makes no difference to the readings
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Yes, I set the maximum distance at 300 but then the sensors return 0's. All the sensors are pointing at a solid wall 250cm away, but the sensors are returning 0's rather than seeing the wall, thus I'm assuming out of their range. I thought it strange as the Hr04's measured/worked fine over this distance. I've tried different delay times to see if there is any interference, up to 100ms but it makes no difference to the readings

Are you sending the sensor 5v?  Other than that, must just be your sensors.

Tim
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yep, even gave them an external 5v input but no change to the distance.....
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Hi! Fantastic library.

I simply want to use 2 HC-SR04 sensors and use the result to turn on their appropriate LED when MAX_DISTANCE is less than 30.

SR04 #1 - turns on LED1 when MAX_DISTANCE is less than 30
            - turns off LED1 when MAX_DISTANCE is greater than 30

SR04 #2 - turns on LED2 when MAX_DISTANCE is less than 30
            - turns off LED2 when MAX_DISTANCE is greater than 30


I added an if/else statement in the pingResults() function, LED 1 turns ON and remains on when
either sensor is triggered.
What do I have to do to declare both sensor 1 and sensor 2 in the function?  

Sounds pretty simple but I'm kinda new at this so be gentle!  smiley

Thanks.


Here's the sketch:

#include <NewPing.h>

#define SONAR_NUM      2
#define MAX_DISTANCE 30
#define PING_INTERVAL 33
//LED setup
#define LED_1   12
#define LED_2   13

unsigned long pingTimer[SONAR_NUM];
uint8_t currentSensor = 0;

NewPing sonar[SONAR_NUM] = {  
  NewPing(4, 5, MAX_DISTANCE),
  NewPing(6, 7, MAX_DISTANCE)  
};

void setup() {
  pinMode(LED_1, OUTPUT);
  pinMode(LED_2, OUTPUT);
  
  Serial.begin(115200);
  pingTimer[0] = millis() + 75;
  for (uint8_t i = 1; i < SONAR_NUM; i++)
    pingTimer = pingTimer[i - 1] + PING_INTERVAL;
}

void loop() {
  
  for (uint8_t i = 0; i < SONAR_NUM; i++) {
    if (millis() >= pingTimer) {    
      pingTimer += PING_INTERVAL * SONAR_NUM;  
      sonar[currentSensor].timer_stop();  
      currentSensor = i;                  
      sonar[currentSensor].ping_timer(echoCheck);
    }
  }


}

void echoCheck() {  
  if (sonar[currentSensor].check_timer())
    pingResult(currentSensor, sonar[currentSensor].ping_result / US_ROUNDTRIP_CM);
}

void pingResult(uint8_t sensor, int cm) {  // Sensor got a ping, do something with the result.
  // The following code would be replaced with your code that does something with the ping result.
  
    if (cm < MAX_DISTANCE) {  
      digitalWrite(LED_1, HIGH);
  }
     else {
        digitalWrite(LED_1, LOW);
  
  }
  
  for (uint8_t i = 0; i < SONAR_NUM; i++) {
  Serial.print(sensor);
  Serial.print(" ");
  Serial.print(cm);
  Serial.println("cm");
  }
Serial.println();
  
}

The 15 sensor example sketch is more for advanced users that require a multi-tasking type script where multiple things will be happening at basically the same time.  Therefore, your use is well outside these parameters.

Instead, simply use the basic one sensor example sketch and add a second sensor.

Basically, you're trying to make it much more complicated than it needs to be, which is why you're having problems.

Now, if you had an already event driven sketch and you wanted to add two sensors while still keeping your sketch event-driven, then using the 15 sensor sketch would be appropriate.

Tim
« Last Edit: April 17, 2013, 08:51:54 am by teckel » Logged

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Hi,
I bought a HC-SR04 with Arduino Uno R3.
Without knowing anything, I wired up them together and it works like a charm.
In addition, parameters can be fine tuned (distance, sampling rate...)

Marvellous. It's really plug and play library, and examples given work !
Thank you fo your library.

Sam

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some ideas about accuracy...

i have just gotten my sr04 and played a lithe with it. i intend to use it to measure oil level in a tank. so accuracy is quite important.
after reading on the web there are two main points that seem to influence the accuracy of the sensor and both are not accounted for in the newping library:

- one is temperature. it would be nice to be able to set the temperature that newping uses for the conversion to cm/inces. depending on the temperaure the error can easily be in the range of 10% if temperature is not accounted for.

- the other one is the which echo is received and evaluated. if i do repeated measurements i notice that the results will be relatively near around two or tree that are themselves further apart. this looks like it is consistent with some articles that say this error comes from reading the second or third echo and not the first and should be especialy noticeable in the short range.

so to be able to make more accurate measurements i started reading 10 or 50 pings, iterating over all of them and throwing away all that are equal to the largest and all that are equal to the smallest and then averaging the rest. if there are non available after throwing the smallest and largest away i take the smallest. the conversion to cm is then done in float.

this seems to give very accurate and reproduceable results. doing this repeatedly in a range of 1cm to 1m gives identical results up to at least 1mm.

maybe a 'slow scan' option could add this to the newping library for applications where fast response times are not needed.
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some ideas about accuracy...

i have just gotten my sr04 and played a lithe with it. i intend to use it to measure oil level in a tank. so accuracy is quite important.
after reading on the web there are two main points that seem to influence the accuracy of the sensor and both are not accounted for in the newping library:

- one is temperature. it would be nice to be able to set the temperature that newping uses for the conversion to cm/inces. depending on the temperaure the error can easily be in the range of 10% if temperature is not accounted for.

- the other one is the which echo is received and evaluated. if i do repeated measurements i notice that the results will be relatively near around two or tree that are themselves further apart. this looks like it is consistent with some articles that say this error comes from reading the second or third echo and not the first and should be especialy noticeable in the short range.

so to be able to make more accurate measurements i started reading 10 or 50 pings, iterating over all of them and throwing away all that are equal to the largest and all that are equal to the smallest and then averaging the rest. if there are non available after throwing the smallest and largest away i take the smallest. the conversion to cm is then done in float.

this seems to give very accurate and reproduceable results. doing this repeatedly in a range of 1cm to 1m gives identical results up to at least 1mm.

maybe a 'slow scan' option could add this to the newping library for applications where fast response times are not needed.


1) Because you need an outside thermometer to measure temperature, it was decided not to overly complicate the NewPing library.  However, NewPing *IS* designed to adjust with temperature.  Simply use the ping() method which gives you a time.  Then, do your own calculation of distance based on your thermometer attached to the Arduino.  In almost all situations, the default distance works well for average indoor temperatures.  But, if you need accuracy, you're going to need additional hardware and then (of course) you're going to need to do your own calculation.  But, NewPing will work with this situation just fine.

2) This isn't a problem with the library, nor can it be fixed in a library.  This is fixed by following the instructions in my sample sketches.  Basically, if you ping a second time too quickly after a previous ping, you can get an echo.  This can't be fixed by the library as it's only reading what the sensor outputs, which is a digital signal (the library has no amplitude information).  The solution is to simply heed my warnings in my sketches.  Which is to not ping too quickly.  Your pings shouldn't be more frequently than around once every 29ms.  If you're in a highly sonicly reflective environment, or your sensor is overly sensitive, you may need to increase this amount.  If it's not something fast moving (probably like in your case) ping once every second or two even.  That way, you can be assured that you're not reading an echo.  NewPing doesn't control the speed of the pings *YOU* do.  If you want to make it slow, just make it slow.  Maybe I'm missing something?

Tim
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Hi Teckel,

did investigate the duration2cm() function here - http://arduino.cc/forum/index.php/topic,165860.0.html -
might be useful in your library.
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Hi Teckel,

did investigate the duration2cm() function here - http://arduino.cc/forum/index.php/topic,165860.0.html -
might be useful in your library.

I tried something similar in the past, but honestly it's not worth the extra cycles adding this type of code adds.  Basically, it's pointless to try to make the math more accurate than the sensor is.  Ultrasonic sensors are not very accurate anyway.  Also, there's actually an argument as to the speed of sound (everyone likes to use a different number).  This is why I settled on an integer and the value that I default to.  It provides very accurate distance results in typical indoor temperatures and does so very fast using very little program space.

Instead of getting into this battle, I avoid it.  Just use the ping() method which returns a ping time.  Then, use whatever math you want (based on temperature or whatever).  If you want to use a fraction and want to use a different method to calculate this (like the above linked example) that's fine also.

Keep in mind that NewPing is an ultrasonic ping library, not a floating point, math, or temperature library.  I'm sure you can find or develop a library that allows you to divide a floating point number without using floating point math.  This would be then just included in your sketch along with NewPing to calculate a distance at whatever accuracy level you desired.  But keep in mind that the sensor isn't that accurate anyway (only  about 1cm).  So all this effort may be wasted anyway.

Tim
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The fact that the sensors are not accurate is imho no argument to use math that adds additional errors. The relative errors add up.
That said, I agree with you that most applications do not need this level of accuracy.

Thanks,
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The fact that the sensors are not accurate is imho no argument to use math that adds additional errors. The relative errors add up.
That said, I agree with you that most applications do not need this level of accuracy.

Thanks,

If you want to use floating point values, more power to you, go for it!  NewPing FULLY supports doing this.  *YOU* have the ability to change the US_ROUNDTRIP_CM and US_ROUNDTRIP_IN values to whatever you want, or use ping() and do any other calculations you wish factoring in temperature, altitude, humidity, etc.

The fact is, my integer values are typically more accurate than when people try to over complicate things by using floating point values in attempts to get more accurate values.  But, if you're in search for the holy grail of ultrasonic measurement, use ping() and apply your magic formula.

This is *NOT* something that will be added to NewPing as it's outside the scope of the library to be any more accurate than it is now.  Because, to be more accurate you'd need a thermometer, and apply your own formula.  So, while this is a fine topic, it shouldn't be here as it will never be added to NewPing.  Heck, there's debate on the speed of sound, I'm just staying out of the fight.

Topic closed.
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yes. i do think you missed something.

if i run the new ping sampe code i get a minimum error of 1cm or 2cm even in an absolutely stable setup, if i change the calculation to float the error is a little bit smaller but still in the range of 1cm. and both will give no stable values. the results fluctuate with ever line on the console.

if i use my 'slow' method to measure i get an error that is in the range of 1mm and absolutely stable values. no fluctuation. repeated measurements give the same distance again and again.

this is a huge difference for my application. and now it makes sense to appy the temperature correction.

if you say that this is not your intendet usage scenario that is fine with me. but to say the sensors are inherently so bad that nothing can be done ist just plain wrong.
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yes. i do think you missed something.

if i run the new ping sampe code i get a minimum error of 1cm or 2cm even in an absolutely stable setup, if i change the calculation to float the error is a little bit smaller but still in the range of 1cm. and both will give no stable values. the results fluctuate with ever line on the console.

if i use my 'slow' method to measure i get an error that is in the range of 1mm and absolutely stable values. no fluctuation. repeated measurements give the same distance again and again.

this is a huge difference for my application. and now it makes sense to appy the temperature correction.

if you say that this is not your intendet usage scenario that is fine with me. but to say the sensors are inherently so bad that nothing can be done ist just plain wrong.

Maybe you need to turn on rounding in the header file?  #define ROUNDING_ENABLED true

I get stable values with no fluctuations with my library without any modifications with all the sensors I have.

The math doesn't change from sensor reading to sensor reading.  So, if the sensor is outputting the exact same ping time, the exact same distance calculation will occur.  With this said, it does depend on how it's rounded.  By default, NewPing truncates the distance calculation.  So if the distance is say 50.95cm it could flip between 50 and 51cm.  This has to do with the margin of error of the sensor, which is around 0.33cm.  With the rounding enabled, the same situation as shown above would yield a stable 51cm.

I think you've confused the accuracy of the sensors and the method of time to distance calculation.  But, in all cases, you can simply just use the ping() method which just gives you the ping time.  Then, you can do whatever logic you wish to convert this to a distance.  The ping_cm() and ping_in() methods are meant to be a down and dirty, fast, and tight way of getting accurate results.  This works for 99.9% of people best.  But, if you're in the 0.01% that must use a different formula and use a thermometer to get more accurate results, NewPing is already set to work for you, just use the ping() method.

Basically, what I'm saying is that you should use the ping() method and use your own math.  NewPing is not the place to debate the speed of sound (which is yet another debate that 0.01% of people want to get into).  I'm not getting into this and won't be changing NewPing making it bigger and more complex for 0.01% of people.  One of the primary goals of NewPing is to be smaller and faster than other ping libraries.  While adding rounding and temperature calculations could make it ever so slightly more accurate, it's simply not within the scope of the project, and what the ping() method is exactly designed for.  So please, use ping() and this can be the last I hear of time to distance calculations, it's an old, dead, and boring topic that I don't wish to debate further.

Tim
« Last Edit: June 18, 2013, 11:46:41 am by teckel » Logged

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I'm trying to use an SR04 with the single-pin method, but I can't get it to work.  I've tried it with two different identical looking sensors purchased from Amazon and eBay.  This is on an Arduino Uno (might be a SainSmart recreation but it looks like an authentic one, not sure.

What troubleshooting steps can I try?
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