[TriEmbed] ping sensor accuracy?

[Rodney Radford]

Any sonar based system has the issue that it is sending out a cone of sound
and receiving a reflected cone of sound, so it is basically averaging the
distance to it and the objects nearby.  This is especially visible if you
are using one to sweep walls leading into and out of a corner of the room.
As you sweep one wall, you will get very linear distances to the wall, but
as you approach the vertex, it is as if the corner morphs into a curve
(since we are getting reflections from both walls) and then back out to a
linear reading on the other wall.

Other than that, I have been very happy with them and get accurate and
repeatable readings from them.

So I would first check to see if perhaps there is something nearby causing
a confusion to the sensor, but not sure why that would vary if the walls
and sensor are not moving.  I also have not used it against water and
wonder if perhaps that is the issue.

Try taking the same sensor and point it at a wall with nothing else in the
way and see if your readings improve.  If so, you know it is something
about the environment or item you are measuring.  if not, it is something
with your sensor or the way you are measuring the pulse width.

There are commercial water depth sensors that work with ultrasound, so I
know it is possible - I just have not tried it with the cheap hobby sensors.



On Thu, Jul 28, 2016 at 11:47 AM, Alex Davis via TriEmbed <
triembed at triembed.org> wrote:

> Anyone try those ultrasonic rangefinder ‘ping’ devices? Were you able to
> get any precision from them? I have mine pointed at a still pool of water,
> and get the following results:
>
> got request from : 0x1:  humidity % = 74.94, temp C = 29.42, height cm =
> 195
> got request from : 0x1:  humidity % = 75.30, temp C = 29.43, height cm =
> 172
> got request from : 0x1:  humidity % = 75.57, temp C = 29.42, height cm =
> 173
> got request from : 0x1:  humidity % = 76.06, temp C = 29.44, height cm =
> 173
> got request from : 0x1:  humidity % = 75.20, temp C = 29.53, height cm =
> 173
> got request from : 0x1:  humidity % = 75.06, temp C = 29.56, height cm =
> 143
> got request from : 0x1:  humidity % = 75.56, temp C = 29.56, height cm =
> 172
> got request from : 0x1:  humidity % = 76.20, temp C = 29.59, height cm =
> 172
> got request from : 0x1:  humidity % = 76.90, temp C = 29.61, height cm =
> 145
> got request from : 0x1:  humidity % = 77.80, temp C = 29.64, height cm =
> 145
> got request from : 0x1:  humidity % = 77.67, temp C = 29.65, height cm =
> 172
> got request from : 0x1:  humidity % = 75.59, temp C = 29.66, height cm =
> 166
> got request from : 0x1:  humidity % = 76.22, temp C = 29.73, height cm =
> 143
> got request from : 0x1:  humidity % = 76.74, temp C = 29.83, height cm =
> 172
> got request from : 0x1:  humidity % = 76.16, temp C = 29.88, height cm =
> 165
> got request from : 0x1:  humidity % = 76.09, temp C = 29.94, height cm =
> 172
> got request from : 0x1:  humidity % = 75.67, temp C = 29.94, height cm =
> 167
> got request from : 0x1:  humidity % = 76.20, temp C = 29.95, height cm =
> 167
> got request from : 0x1:  humidity % = 76.61, temp C = 29.96, height cm =
> 174
>
> That’s pretty bad, in my opinion. I’m wondering if it’s due to running it
> on 3.3v? I know it’s spec’ed for 5v. I was hoping to use 3.3v so I could
> use a solar charged 3.7v LiPo cell, but I suppose I could switch over to a
> 6v lantern battery and use one of the circuits here: http://forums.pa
> rallax.com/discussion/152308/ping-sensor-3-3v-compatible
>
> Lantern battery isn’t rechargeable, but an Energizer-brand alkaline is
> rated for 56 Ah, so that ought to last a long time.
>
> Alex
>
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