Comment by Andrew Radford on July 29, 2011 at 1:56am

Don't some of the sensor models already have PWM (and serial?) out? I remember seeing that in a datasheet somewhere...

Comment by agmatthews on July 29, 2011 at 2:44am

Andrew,

Yep you are right

The Maxbotix Sonars have PWM and Serial as standard.

The serial ports on the APM main board are already in use and at 9600bps its a bit slow and the maxbotics implementation of serial is a bit screwy with inverted RS-232 - that rules all but out serial.

PWM is the recommended "most accurate" way of using the Maxbotics modules (from the data sheet), however measuring the pulse length on a digital pin on a ATMega / Arduino with the 'pulseIn' function is a blocking action (ie the rest of the code stops while it measures the pulse).

I did not want to put any blocking code on the main autopilot and risk slowing down the DCM/IMU functions. So I run all the PWM code and all the noise filtering on the Arduino mini. The main Arducopter code then just does an I2C request for the data when it wants it

I used the barometer code in APM_BMP085 library as a template. I'll attach my library up above in the main post

There's plenty of spare capability on the Arduino mini in this example.

I've been wondering what else I could use it for...... any suggestions

 

Comment by Bernard Michaud on July 29, 2011 at 6:17am

How about shielded wire to prevent RF from getting involved in noise building (Sonar power and signal cable proximity). As anyone tryed this before ?

Comment by agmatthews on July 29, 2011 at 6:26am

Some folks are reporting good results with shielded cable AND relocating their sonar. So it's a bit hard to tell which one fixed the noise problem.
Ive not seen any results either good or bad with just shielded cable on the analog signal.

I could diminish the noise on my sonar by moving one ESC about 10mm away from the cable/IMU board. However it would return just when I didn't want it too.

Comment by diego colonnello on July 29, 2011 at 7:20am

this can be done with the Parallax PING))) sensor????

Comment by Bernard Michaud on July 29, 2011 at 7:34am

Need to know what is Parralax PING sensor. Thanks

3D Robotics Comment by Chris Anderson on July 29, 2011 at 8:03am

Impressive! Have you compared that with the recommended solution of just mounting the regular sensor three inches away from the ArduCopter body?

 

Comment by afernan on July 29, 2011 at 3:26pm

I,m tested all posibilities. I,ve started shielding all power and signal cables AND moving far from ESC the sonar (not to much, to avoid longer cables) . It solved completely the problem. Then I relaxed a bit the thing, and I put again standar rc cables, but sonar moved away. Still very good, but sometimes crazy jumps apeared (noise).

My final conf is shielding only the signal cable, moved away ESC and avoid connectors (cable directly welded to APM). The result is a rock solid alt-hold. I'll post some video.

Comment by agmatthews on July 29, 2011 at 4:03pm

@Chris, I proved that in my case the noise was at least partly the result of the conar cable passing too close to one of the ESCs. @afernan seems to have done a different series of tests with the same result (ie it's the cable where the noise is coming from rather than the sonar module)

Shielded cable or going I2C allows folks to continue use Jani's jdrones sonar mounts.

The I2C experiment is probably a bit over the top when shielded cable gives similar results but it was an interesting journey and gives a template for adding future sensors or outputs without needing any APM hardware pins

Comment by agmatthews on July 29, 2011 at 4:18pm

@diego colonnello and @Bernard Michaud

Yes you could easily modify this you use a Parallax PING))) sensor

Following this tutorial you would just change the readsonar.pde in my code to interact with the parrallax sensor by sending a pulse to it before waiting for data back

Something like this:

int ReadSonarPulse()
{
long val = 0;

  pinMode(SONAR_PULSE_IN_PIN, OUTPUT);
  digitalWrite(SONAR_PULSE_IN_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(SONAR_PULSE_IN_PIN, HIGH);
  delayMicroseconds(5);
  digitalWrite(SONAR_PULSE_IN_PIN, LOW);
  pinMode(SONAR_PULSE_IN_PIN, INPUT);
 
  val = pulseIn(SONAR_PULSE_IN_PIN, HIGH,(US_PER_CM*MAX_RANGE)+1000); 
  val = val / US_PER_CM; 
  return((int) val);
}

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