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361  Using Arduino / Sensors / Re: Question on ultrasonic sensor! on: August 27, 2012, 04:50:06 pm
Will it work underwater is the question, and your car sensors I'm sure wouldn't.
I thought we'd moved away from that, and were measuring the void above the liquid surface, where the worst we could expect would be vapour or condensation.

If that's the case, I answered the poster in the 3rd reply to this thread.

362  Using Arduino / Sensors / Re: Too many if statements?? Please help on: August 27, 2012, 04:47:03 pm
teckel I don't know how much more detail I can give.  As I said.  Each individual IF statement within the Loop() works perfectly fine and in any pair of two they work great but if I try to use three or more, nothing happens with ANY of the sensors.  Nothing will trigger an output.  I will try your advice and include a print statement at the beginning of each IF within the loop() and see what happens.

First, you never said you were speaking of the IF statements in loop().  Up until now, you only mentioned the IF statements, which also exist outside loop(), which is why I asked.  Please review what you wrote, you may have *thought* you said inside loop(), but you did not.

Secondly, all you've said is that "nothing works".  Do you mean that you start the sketch and nothing AT ALL happens no matter what?  Or, do you mean that the first thing works and the second doesn't?  Or, maybe some things work, but it doesn't work prefect?  Maybe try to give at least a sentence description of what happens from the time you start your sketch.  Or, we are all to assume what you're experiencing, and maybe assuming different things or more importantly different from what is actually happening.

Keep in mind that we're trying to help.  So, you should try to be as descriptive as possible.  It's one thing to take your car in for service and say it doesn't work as they can see your car to diagnose it.  But, we don't have that luxury here as we don't have your hardware in front of us to diagnose.  So, it's very important to give details and be descriptive.

363  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 27, 2012, 04:29:58 pm
Let me simplify and round to make it easier to discuss.  We will use your method of only 1 unit.  First send out a single ping and wait up to 100ms.  Each 1ms is about 1ft, 2ms round trip.  Measure the integer number of msecs rounding down.  Let's assume the result is near the middle between 20-21 about 20.5.  We don't need to be more exact than that.  Now send out 100 pings exactly 1ms apart.  Measure the return values mod 1000us.  This gives us the part to the right of the decimal.  We already know 20ms.  Average them.  We might get 522us.  So the answer is 20.52ms.  The last 2 is not significant.  Convert to feet. 

You can see we don't need to identify which ping is which.  It doesn't matter since they're all sent at x.000 secs.  This could be relative to nothing, or GPS time.  But we could figure it out since we know the object is about 20.x ms away.  When a ping comes 20.51ms later we know it was sent 20+us ago, not 19 or 21.

This would not work if the object were exactly 20.01ms away, because we would hear the ping being sent each 1ms.  It would be much louder and block us from hearing the echo.  But it would work with 2 devices using an accurate clock!  Or you could just change the interval to 1.12ms instead of 1.0ms if your echo was being blocked.  More complicated math.

The advantage of my idea is that you get 100's of pings per second to average, even if the target is far away.  This will let you calculate an accurate distance much quicker than waiting 100ms between sending, if you want an answer in 0.3 secs.

If you like my idea you an have it!

Sending pings out every 1ms would be too quick as it could take up to 29ms for that ping to arrive.   A ping every 1ms would only work if you were measuring distances of less than around 34cm.  Anything further than that would require a longer time between pings.  I was assuming you were wanting to measure up to 10m (the max sensor distance).  If so, you couldn't ping faster than once every 29ms.  If you only were going to measure within 34cm, then you could send a ping out every 1ms.

And that's just the start of the problem.  Conventional ping sensors would still have a problem for three reasons.  First, when you tell a ping sensor to send out a ping, it takes it's good old time doing it.  I haven't found one that takes less than 440 microseconds (7cm worth) of waiting around before it starts.  Some can take over 88ms!  Secondly, some sensors go inactive for a while after a ping is received, or even longer if a ping is not received (like 32ms!)  Finally, existing sensors don't listen for an echo till that same sensor sends out a ping first.  In other words, the receiving sensor isn't even listening when the sending sensor is sending out pings.

Maybe I don't understand what you're trying to accomplish.  Do you want to ping 100 times a second?  You can almost do that already with the NewPing library if your sensor allows it.  Or, are you trying to make an ultrasonic sensor work for further than 5m?  And if so there are sensors that work up to 50 feet away already.  But, the technique you're speaking of would not allow you to send 100 pings per second and measure the distance from 10m away.  Pinging every 29ms for 10m or pings every 1ms for distances within 34cm would be possible.  But only with custom designed ping sensors and receivers and accurately synced devices.

I guess I just don't see what you're trying to do, as you can already ping at very high speeds with the NewPing library with sensors that support it (not quite 1ms, but every 3ms works for distances of about 50cm).  It's also a bit of an issue outside the scope of the NewPing library as you would need custom hardware and special hardware to sync the two systems.  More of a specialty thing rather than a public library.

364  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 27, 2012, 10:27:22 am
Interesting discussion Tim.  I disagree about timestamps.  Here's how to synchronize 2 Uno's to 2us.
As you can see they stay in sync even without GPS once initialized.,120288.0.html

Synchronizing two are not the issue, it's knowing when the ping was sent so you know how long it took to get there.  How do you know WHICH ping you're getting?  Without knowing when the ping was sent, how can you possibly know how long it took to get there?

Let's say that you've synced two ATmega's to within 15 microseconds (that accuracy would be plenty).  One starts sending out pings every 2 millisecond which the other would receive.  Even though they're synced, how does the receiving unit know when that ping was sent to be able to calculate the time and therefore the distance?  Without the start time reference, I can't see how you would measure distance.  For the sake of argument, the receiving unit gets the ping, what values are you using to calculate for distance?  You have receive ping time, so what's the start time?  You need both start and end time to calculate the time it took to send the ping.  You know the pings are 2ms apart, but where do you get the start time?

You *could* measure acceleration/deceleration by measuring the time between the pings.  But, that wouldn't need the two units to be time synced anyway, and would do nothing to measure distance.  Only "hotter" or "colder" would be known.

365  Using Arduino / Sensors / Re: Question on ultrasonic sensor! on: August 26, 2012, 10:50:13 pm
My car has both front and rear ultrasonic sensors.
I would have thought that they'd be at least IP65 to withstand rain hitting them at over 160 kph.

The issue is not if a sensor that can withstand rain (obviously, they can as weatherproof ultrasonic sensors exist).  The issue is will it actually work while submerged.  Put your car under water, back up, and see if the sensors works.  I would guess they won't.  The ability for the sensor to withstand rain at 160kph is meaningless in this context.  Will it work underwater is the question, and your car sensors I'm sure wouldn't.  But, I would suggest trying, just to be sure ;-)

366  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 26, 2012, 10:37:41 pm
There must be a way to SEND a ping every 5ms.  Once you know the rough distance, there's no need to put a timestamp on each ping.  You already know the rough distance, hence how many integer ms it takes.  When you send them at 2-5ms intervals you're now trying to measure the 100us interval.  0.1ms which you add to the integer rough distance you already found.  0.1ms or 0.05ms can be obtained by averaging many samples.  Forget about all this for a minute, it's not my main point.  Let's just use your 50ms interval with no timestamps.

Wouldn't the distance or range increase greatly with 2 devices, sender and receiver in sync?

Around double the distance.  So maybe up to 10 meters for very inexpensive SR04 type sensors.  There are commercial sensors that have a range of up to 50 feet, so using two sensors that range could be as high as 100 feet.

In the case of an Quadcopter, you would need to have two synchronized timers.  I'm not sure if this is the environment you're really considering, but you wouldn't need synchronized timers if you could tie the send and receive sensors to the same Arduino.  There could be an issue with wire length, however.

I still think you'd need a time stamp, unless you're only trying to measure acceleration, which may be possible as the distance between the pings would vary due to acceleration.

367  Using Arduino / Sensors / Re: Too many if statements?? Please help on: August 26, 2012, 01:19:17 am
I am writing a program that reads multiple sensors on the Analog input pins and because I don't really understand how to initiate the switch/case parameters I am using if statements.  The sketch works fine when only using 2 IF statements but when I get to the third nothing works.  I didn't think there was a limit to the number of IF statements but am I wrong?  Each IF statement is exactly the same so it's not syntax errors or anything like that.  I am at my wits end trying to get this to work.  Please help with any input possible.  In the mean time I will keep working on it.  Thank you in advance for any input.

Auto Format is your friend!  Or it should be.

Are we to assume that you're talking about the IF statements in loop() or are you talking about playfile(char *name)?  And could you be anymore general than "nothing works"?

Your problem isn't IF statements or not using CASE statements.  Your problem is one of your code having some kind of bug.  Very hard for anyone to help when you're being so general and not giving specifics.

A good way to diagnose your problem is to put statements like the following inside your IF statements (as the first command).


With each command being a different number, letter, or something to describe each IF statement.  Then, when you run your sketch you open the Serial Monitor so you can track where the code is and when it's failing.

In any case, it's not the fault of Arduino and using too many IF statements or needing to use CASE.  The problem is your code is wrong.  And for us to help specifically you should give DETAILS.

368  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 26, 2012, 01:03:26 am
Thinking...  Instead of measuring the time of a reflection returned from an object.  What if we had 2 devices synchronized by GPS or an accurate clock.  One sending the ping, the other receiving it.  If we can measure the delay within 1-2us that would be accurate.  Roughly 0.01".  Obviously that is not possible because of the physics of a sound wave. 

What is the theoretical limit using the frequency of the ultrasonic sensors in this configuration? 
It's the same as the normal method.
Let's use 100khz as an example.  Each cycle is 10us.  So 1/10"?  Certainly <1/2".  Averaging multiple readings.

Wouldn't this greatly increase the range compared to using only 1 device?

You could send a ping every 2ms once you know the rough distance. 
Then you'd have 500 measurements to average in only 1 sec, regardless of the distance.

Obviously the limitation would not be the accuracy of the PPS clock, since GPS is +-10ns.
10ns is about 10ft at the speed of LIGHT!
We'll leave that for another LightPing Library...

How can I use this method with the receiver in a Quadcopter?
The problem is the sound from the motors and blades.
The obvious answer is to put the transmitter in the air,
the receiver on the ground where you want to land, then Xbee to send the data.
This works much better, with a huge increase in range, compared to reflecting from the ground when it's grass.


The current ping sensors I've found can't ping that quickly.  I'm finding some ping sensors now that can't really ping faster than about 48-49ms, and none can faster than once every 29-32ms.  Basically, they initiate a ping, then you can't initiate another ping till some set time has passed.

Also, when you initiate a ping they take a little while before they actually start (around 450uS).  This varies greatly from device to device.  My library waits for the sensor to be ready so an accurate measurement is taken.

Finally, when sending a large number of pings, there's no way the receiving sensor would be able to know when the ping that arrived was sent.  The only way that would be possible is if the ping itself actually contained a timestamp.

Without some kind of time stamp on the ping itself, very accurately synchronized sensors, and custom built sensors that would ping on command, it's not really possible.  There are probably easier ways of doing it, albeit probably just as expensive.

369  Using Arduino / Sensors / Re: Question on ultrasonic sensor! on: August 24, 2012, 12:52:02 pm
If I keep the ultrasonic sensors (40KHZ/25KHZ) in a sealed plastic container, will they still measure the distance? I want to measure the water level in a tank about 10ft depth and I don’t have the water proof ultrasonic sensors available at my place. Any suggestions are welcome.

I don't know your exact usage, but maybe instead of measuring the depth of the water from the surface down, you could measure the distance from above the surface to the water's surface.  Then, with a known surface level and depth, you could easily calculate the depth.

In other words, put the ultrasonic sensor let's say 1 foot above the surface of the water.  The sensor would measure the distance as 12 inches.  You then measure the distance from the sensor to the bottom of the tank, lets say it's 132 inches.  So, when the sensor reads 12 inches, you would do 132-12=120 inch water depth.  When the sensor reads 15 inches, 132-15=117 inch water depth.

While the ultrasonic sensor won't work under water, the ping will reflect off the water's surface.  Not knowing your exact usage maybe this won't work.  But, if it's a tank, it has a static depth and probably a place to mount the sensor above water.  If you do choose to use an ultrasonic sensor, may I suggest the NewPing library which has a ping_median method that would work nicely to filter out noise and get an accurate measurement with something like this that's probably not moving quickly.

370  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 23, 2012, 02:40:34 pm
fairorgan got me to thinking about exactly how much processing time is spent using the ping_timer method.  Which also helps to understand what else your sketch could be doing in the remaining time.  So, I wrote a sketch to tests this.  The sketch runs for 30 seconds and logs how much time is spent both initiating the ping and checking for the return echo.  It's not perfect, as there's some overhead in doing these calculations making these estimates a little on the high side.  Anyway, here's the results with pings happening every 29ms.

5cm pings = <1% load
20cm pings = 2% load
70cm pings = 7% load
125cm pings = 12% load
200cm pings = 19% load
500cm pings = 45% load

When reducing the maximum sensor distance value when calling the NewPing constructor, you can greatly reduce the maximum ping_timer load.  For example, if you leave it at the default of 500cm, using ping_timer every 29ms will use up to 45% processor load.  However, lowering the max distance to 200cm means the maximum load can be only 19%, or lowering it to 50cm makes the max load only 5%.  So, setting a maximum distance to the longest distance you need will greatly free up the ATmega to do other parts of your sketch.

The ping frequency also effects the processor load.  The above numbers were all done at a 29ms ping rate.  However, if the ping rate is every 100ms, the load is drastically reduced to only 5.5% (down from 19%).  200cm maximum distance and pinging every 50ms uses a maximum of 11% processor load.

So, when creating an interrupt driven sketch and using NewPing, setting the maximum sensor distance and ping rate to what you really need for your project will greatly effect how much processing time you have available to do other parts of your sketch.  Doing a maximum ping rate of 29ms and leaving the default maximum distance at 500cm will use almost half of the ATmega processing time (45%).  If your project really only needs to sense out to 200cm and pinging once every 100ms is all the faster you really need, you've lowered the processing time down to only 5.5% (almost 1/10th the load).

Keep in mind that these are maximum load amounts.  If the a ping echo is sensed at a shorter distance, the load can be greatly reduced.  For example, the 45% load for a max distance of 500cm at a 29ms ping rate is only if there's a NO_ECHO (zero value).  If under the same settings there's a constant ping echo at 10cm, the load is only 1%.  So, these are truly worse case numbers.  But, to avoid your sketch to be sluggish at times, you should consider the worst case scenario.

371  Using Arduino / Sensors / Re: What to do when I run out of analog inputs? on: August 22, 2012, 05:35:57 pm
I'm using the analog inputs on the Arduino Uno R3 to measure voltage values between 0-5V. I ran out of analog inputs. Is there a way to expand the amount of analog inputs? Can the digital pins be used as analog input pins?

Sorta un-related side question:
Whenever I have the Arduino Motor shield on top of the Arduino board, I notice that the A1 + A0 inputs no longer are able to sense any voltage values and the A2+A3 inputs are always measuring 5V, even when open. Is the motor shield broken? Is this abnormal behavior? Therefore, Im looking for other ways to increase the analog input sensors.

I suggest the Teensy board.  It's only $16 and has 12 analog inputs.  It's also wonderfully small and complete with USB.  It's like a micro version of a Leonardo.  Love it!

372  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 22, 2012, 05:08:59 pm
I was actually only thinking of using two SR-04 sensors (at most three), but like your use of the array in the 15 sensor example for holding the data. Would I be better just duplicating the new ping_median once per sensor and not use an array nor interrupt method?

My project: I am controlling a robot’s head position via servos, which currently have either remote control (via joystick) or automatic random positioning of x and y axis. I would like to add the ability for close object tracking of the x axis, so thought the best way would be two ultrasonic sensors pointing slightly apart concealed on the head itself, and in the event of an object coming within say a couple of metres range, the head will stop random movements and track the object in x axis by moving the servo to keep the signal from both ultrasonic sensors the same, until either the object goes out of range or the robot gets bored.

If you just wanted to use an array to store the ping results, you could easily modify the 15 sensor sketch to work with ping_median instead of ping_timer.  The problem is that the sketch would no longer be interrupt driven, and would be waiting for ping echos instead of doing anything else (like positioning the servo on the robot or doing probably much of anything else).  For example, if you had 3 sensors and each sensor would take 5 samples to find the median that would be a total of 15 pings with at least a 29ms delay between each or a total of around 435ms (about 1/2 second) every ping cycle where your robot can do nothing but read the sensors.  Not at all interrupt driven like the 15 sensor sketch where very little time is wasted monitoring the pings and you're free to do other things what seems like the same time.

A better solution is to continue to use the 15 sensor sketch as a base, but use oversampling to read the sensors multiple times, then average the results.  Here's an example sketch:

#include <NewPing.h>

#define SENSORS        3 // Number or sensors.
#define ITERATIONS     5 // Iterations for each sensor.
#define PING_NUM ITERATIONS * SENSORS // Calculates the number of pings.
#define MAX_DISTANCE 200 // Maximum distance (in cm) to ping.
#define PING_INTERVAL 29 // Milliseconds between sensor pings (29ms is about the min to avoid cross-sensor echo).

unsigned long pingTimer[PING_NUM]; // Holds the times when the next ping should happen for each sensor.
unsigned int cm[PING_NUM];         // Where the ping distances are stored.
uint8_t currentSensor = 0;         // Keeps track of which sensor is active.

NewPing sonar[PING_NUM] = {      // Sensor object array (Each sensor's trigger pin, echo pin, and max distance to ping).
  NewPing(12, 11, MAX_DISTANCE), // Sensor 0, sample 1
  NewPing(2, 3, MAX_DISTANCE),   // Sensor 1, sample 1
  NewPing(4, 5, MAX_DISTANCE),   // Sensor 2, sample 1
  NewPing(12, 11, MAX_DISTANCE), // Sensor 0, sample 2
  NewPing(2, 3, MAX_DISTANCE),   // Sensor 1, sample 2
  NewPing(4, 5, MAX_DISTANCE),   // Sensor 2, sample 2
  NewPing(12, 11, MAX_DISTANCE), // Sensor 0, sample 3
  NewPing(2, 3, MAX_DISTANCE),   // Sensor 1, sample 3
  NewPing(4, 5, MAX_DISTANCE),   // Sensor 2, sample 3
  NewPing(12, 11, MAX_DISTANCE), // Sensor 0, sample 4
  NewPing(2, 3, MAX_DISTANCE),   // Sensor 1, sample 4
  NewPing(4, 5, MAX_DISTANCE),   // Sensor 2, sample 4
  NewPing(12, 11, MAX_DISTANCE), // Sensor 0, sample 5
  NewPing(2, 3, MAX_DISTANCE),   // Sensor 1, sample 5
  NewPing(4, 5, MAX_DISTANCE)    // Sensor 2, sample 5

void setup() {
  pingTimer[0] = millis() + 75;          // First ping starts at 75ms, gives time for the Arduino to chill before starting.
  for (uint8_t i = 1; i < PING_NUM; i++) // Set the starting time for each sensor.
    pingTimer[i] = pingTimer[i - 1] + PING_INTERVAL;

void loop() {
  for (uint8_t i = 0; i < PING_NUM; i++) { // Loop through all the sensors.
    if (millis() >= pingTimer[i]) {        // Is it this sensor's time to ping?
      pingTimer[i] += PING_INTERVAL * PING_NUM;   // Set next time this sensor will be pinged.
      if (i == 0 && currentSensor == PING_NUM - 1) oneSensorCycle(); // Sensor ping cycle complete, do something with the results.
      sonar[currentSensor].timer_stop();          // Make sure previous timer is canceled before starting a new ping (insurance).
      currentSensor = i;                          // Sensor being accessed.
      cm[currentSensor] = NO_ECHO;                // Make distance NO_ECHO in case there's no ping echo for this sensor.
      sonar[currentSensor].ping_timer(echoCheck); // Do the ping (processing continues, interrupt will call echoCheck to look for echo).
  // The rest of your code would go here.

void echoCheck() { // If ping received, set the sensor distance to array.
  if (sonar[currentSensor].check_timer())
    cm[currentSensor] = sonar[currentSensor].ping_result / US_ROUNDTRIP_CM;

void oneSensorCycle() { // Sensor ping cycle complete, do something with the results.
  unsigned int uS[ITERATIONS], last;
  uint8_t i, j, x, it, ii;
  for (x = 0; x < SENSORS; x++) {
    uS[0] = NO_ECHO;
    it = ITERATIONS;
    ii = 0;
    for (i = 0; i < ITERATIONS; i++) {
      last = cm[x + (i * SENSORS)];
      if (last != NO_ECHO) {   // Ping in range, include as part of median.
        if (i > 0) {           // Don't start sort till second ping.
          for (j = ii; j > 0 && uS[j - 1] < last; j--) // Insertion sort loop.
            uS[j] = uS[j - 1]; // Shift ping array to correct position for sort insertion.
        } else j = 0;          // First ping is starting point for sort.
        uS[j] = last;          // Add last ping to array in sorted position.
        ii++;                  // Next ping in insertion sort array.
      } else it--;             // Ping out of range, skip and don't include as part of median.
    Serial.print(uS[it >> 1]);
    Serial.print("cm ");

The above sketch is 3 sensors with 5 times oversampling.  Instead of just printing the results in the oneSensorCycle function, it does the same insertion sort/median calculation as NewPing does with the ping_median method.  It pings each sensor (0,1,2) then repeats 5 times.  For example, the ping order is: 0,1,2,0,1,2,0,1,2,0,1,2,0,1,2.  This sketch will also accommodate different oversampling (iterations).  Just change the ITERATIONS define and sonar array to match.

The advantage is that this sketch is totally interrupt driven.  So, the ATmega has all kinds of time to do other things.  While pinging, every 24uS it checks for a ping echo, but the rest of the time your sketch can do other things (like rotate a servo, move, etc).  Once a full 3 sensor, 5 oversample pass is made, it goes to the oneSensorCycle function where the median values for the 3 sensors are calculated, which is very quick and only takes about 30uS.  Basically, the ATmega is free to do other things at the same time it's pinging.  Just be sure to not use any delay statements in your sketches!

373  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 21, 2012, 05:53:28 pm
Your code works fine for me.  I guess a loose connection could the the source of the problem.  But, it could also be that you're trying to get a ping that's just too far away.  These sensors really don't work all the way out to 400 or 500cm.  They seem to work okay to about 200cm for most, but I have some sensors that won't read anything consistently beyond around 75cm.  This is the fault of the sensors, not the library as the same thing happens with other libraries or with no library at all.  Try putting something 50cm away from the sensor and see what happens then.  It's just suspicious that it stops working around 200cm and then in your next test all the results are within 200cm.  Maybe it would work without you holding the sensor if all the readings were <50cm?  But, if it is a lose connection, that could also be why it's crashing after a few minutes, it's simply shorting out.  BTW, I've *never* got a zero reading that wasn't for a logical reason and I've *never* had any of my Arduino or Teensy 2.0 crash while using the NewPing library.  And, I've sometimes ran them for several hours or even overnight without a single issue.

374  Using Arduino / Sensors / Re: NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.5 on: August 21, 2012, 08:32:46 am
Fantastic job with this new library!

I am especially liking the median feature of v1.5 to eliminate rogue results, but how can this be integrated into the 15 sensor example sketch which does not use ping() but sonar.ping_timer(function) instead?

To actually combine the two would be simple.  However, in the process it would lose the interrupt aspect of the ping_timer() method.  I've been toying with the idea, and considering new ways of doing it.  One thing I've considered is a mass ping of all sensors at the same time followed by interrupt waiting for the ping echo.  With 15 sensors there could be crazy cross-talk.  But with 4 sensors it would probably work.

Also consider that with 15 sensors, if it were to poll each sensor 3 times it would take 3 times as long.  Not sure how much processing time you have left after pinging 15 sensors.  But, multiply the time it takes by 3 or 5 and you may no longer have time to do anything else, or the pings are just too slow to sense something in time if your robot is moving at a high enough speed.

375  Using Arduino / Sensors / Re: How to get a degree value of Accelerometer MMA7455? on: August 20, 2012, 03:46:50 pm
The application is to use it as a tilt sensor for a robot

A gyroscope would probably be what you need for a robot tilt sensor.  If you're trying to balance a robot, a gyroscope will work for a short while, then drift will cause it to fall over.  You really need both for a balancing robot.

So, do you want to measure tilt, or are you actually trying to get it to balance?
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