ultra sonic distance sensor

Craig Paul

I have been playing with the Ultra sonic sensor to try and detect a moving object.
I want to be able to tell whether it is coming closer, moving away or staying still.
using the code:


LOW Ping
PULSOUT 6, 5
PULSIN 6, 1, distance
distance = distance ** 2251

running this code twice and then comparing the value of distance. The problem is I need to round off the value of the VAR distance. Otherwise I get a slightly different answer even when things are not changing.
The DEC4 command is just for debug and does not round off the value.

Any suggestions?

Bruce Bates

Craig -

If you will provide us with the entire program, or more of it than you've provided, I'm sure we can offer some suggestions.

Regards,

Bruce Bates

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Steve Joblin

I think you would want your code to do the following:

x· con [noparse][[/noparse]make this the amount of the sensitivity you want]

read the distance
store the distance value in a variable called "prior_distance"

check_sensor
·········· Read the distance
·········· store the distance value in a variable called "current_distance"
···········difference = current_distance - prior_distance
·········· prior_distance = current_distance
·········· if difference is > x then go to big_difference
·········· goto check_sensor

big_difference:
········· do what you want

Vern Graner

Craig Paul said...
The problem is I need to round off the value of the VAR distance. Otherwise I get a slightly different answer even when things are not changing.

As an option, you might want to consider averageing a sequence of pings. I used this code in one of my projects:

cntI var NIB
sample var WORD
AvgDistance con BYTE
RawSample var WORD
PING con 0 'pin for the PING sensor

' **************************
' * PING sonar             *
' **************************
  PINGSend:

  SAMPLE = 0                    ' reset the average ping time accumulator

  FOR cntI = 1 TO 10            ' sample the ping sensor "X" times
    PULSOUT PING, 5             ' Send a ping to check hand position
    PULSIN  PING, 1, RawSample  ' read the return time and store it in "RawSample"
    RawSample= RawSample MIN 100' make sure we don't drop below 0
    RawSample = RawSample/100   ' divide the raw sample by 100 to make it byte-sized :)
    Sample = Sample + RawSample ' Accumulate all the reduced PING samples
  NEXT

  AverageDistance=Sample/10 ' get the average distance

  RETURN

I didn't need the full resolution of the PING, so i reduced the ping result by 100, making it fit into a BYTE variable insterad of a word variable. I then accumulated 10 samples and took the average of those 10 to get a stable (non-jittery) distance measurement. Hope this helps.



Vern

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