Discussion in 'The Projects Forum' started by Hewhowalk, Feb 25, 2010.
Does anyone know an ultrasonic system that could work outdoors?
That is awfully broad. Short range sensors are used to help drivers avoid striking obstructions while backing up. Bats use sonar for navigation in the dark, of course.
What is your interest?
Im considering using it for collision avoidance. But looking for a module with some embedded logic, since the raw data from ultrasonics used outdoors is worthless and im not very skilled in signal processing.
Maxbotix LV-MaxSonar-WR1 Weather Resistant Ultrasonic Range Finder for instance. Any experiances?
There are some alternatives to that, you can find specs on most of them here >> http://www.acroname.com/robotics/info/articles/devantech/srf.html
I have used the SRF04 and the SRF08 modules indoors and out, and they work great.......
There is also this module from velleman which is their parking Radar Kit, I have also built and used this
you can get it here and from other various sources >>>http://www.quasarelectronics.com/velleman/k3502-parking-rader-kit.htm
There should be someone out there that have done a comparision between commercially available ultrasonic modules. My friend Google won't help me in this (or maybe I just don't know how to ask).
In my opinion, the SRF04 would be the easiest for you to implement, it will use 2 IO's on any uc, 1 for the trigger (to send the pulse) and one for the Echo... It is easy to implement using some simple time of flight calculations....
Basically when you pulse the output of the module, you will start a timer, once you receive a echo input from the module you will stop the timer and calculate the distance..... here is a sample code snippet from my Robot based on the OOPIC II uc module, the syntax is in basic but I think it would give you a good reference point to start....
Code ( (Unknown Language)):
'Sound travels 1 inch every 73.746us
'Timer uses 625Khz clock Frequency (5Mhz/8)
'625Khz is 1.6us per clock tick
'Max range of sonar is Approx. 9m (354 inches/ 899cm)
'Distance of echo roundtrip is 354 *2 = 708 inches
'708 * 73.746us /1.6us = 32633 'ticks at max range
'32632 / (354) = 92 --> = inches
'32632 / (899) = 36 --> = cm
INIT.IOLine = 6
INIT.Direction = cvOutPut
INIT.Value = 0
ECHO.IOLine = 7
ECHO.Direction = cvInput
TmrControl.Operate = cvTrue
EchoTimer.Value = 0 'Clear old result
INIT.Value = 1
INIT.Value = 0 'Pulse sonar input
OOPic.Delay = 1 'Give ECHO Chance to go high
'Wait until echo goes low again to return reading
'ECHO might be low already, but could take up to 36ms
'timer automatically runs while echo is high
W1 = (EchoTimer.Value/92) 'Convert to inches
OOPic.Delay = 1
Thx for the code. It will probably be useful later.
But I'm not fully convinced that SRF04 is the way to go. Most modules are as easy to implement as this one and even if it works outside it is not resistant to damp and rain http://www.robot-electronics.co.uk/htm/sonar_faq.htm .
Most sonar modules will not be resistant to rain or moisture, since they use ultrasonic transducer's which need to be exposed and can not be covered or sealed in a container.... but the transducers can be mounted separate from the PCB and have the PCB in a water tight container with leads that go to the transducers..... same concept they use in vehicles with the ultrasonic backup sensors.....
But how well does the tranducers them self stand rain? I have found some modules that are said to work outside, just by putting it inside a pvc-pipe and adding a thin protective film on the end.
Anything placed on the front of the transducer will dampen the acoustic waves coming into it, I have seen some setups (Similar to vehicles) where they will place the transducers in a water resistant container, with holes that the transducers face out of, and the holes are covered with some fine mesh screen, this will not completely protect the transducers, but it will make them somewhat water resistant....
Or you can get water proof ones!! >> http://www.futurlec.com/Ultrasonic_Sensors.shtml, see bottom of page, maybe these could be sued to replace the SRF04 transducers....
That could be interesting. Maybe it's worth checking out.
Otherwise there is this the one I mentioned earlier:
Maxbotix LV-MaxSonar-WR1 Weather Resistant Ultrasonic Range Finder
To bad it's a bit expensive.