hello again,
in order to control the movement of an independent mobile robot i am thinking of using multiple sensors at various positions on it…
mz problem is that ultrasonic sensors maz have interference among them.does anzone know if each of them uses different frequency or any other form of encoding so as not to interfere.
iţve read that this problems does not occur using ir…
for example in the front if i use 2 ultrasonic with an angle between them of 90 degrees there will definitely be an aliasing of signal transmited by the two…or not?
In general IR sensors won’t interfere with each other, unless they are pointed almost exactly the same direction, and what would be the point of that? Their downside is that they have a somewhat limited range, but they come in different ranges, and you may find some that suit your needs.
Ultrasonic sonar sensors generally have a longer range, but multiple sensors will interfere with each other, even different frequencies/brands (even a nice loud clap can mess with some readings). Sonar sensors don’t operate continuously though, they emit short, discrete ultrasonic pulses, then time how long it takes the pulse to return after reflecting off of a surface. An odd reflection of the pulse from Sonar A can trick Sonar B into thinking it’s received an early return pulse.
You can use many sonar sensors on your robot, wait for Sonar X to receive it’s return pulse before triggering sonar X+1. Some people will also set up multiple sonar sensors to fire at exactly the same time, and this works in most cases, but it isn’t an absolute guarantee that the sensors won’t mess up each other’s readings, and it can be difficult to read the many sensors at once.
I’ve used a couple of different sonar sensors, and I’m quite fond of the MaxBotix EZ1. It outputs analog voltage, a pulse width, and TTL serial signals at the same time, which gives you a couple of options of how to daisy chain them, depending on what kind of signal you want to read. You can set up as many of them as you want, trigger the first one, and have it both return it’s reading and trigger the second one and so on, with just one digital I/O line and one PWM or Serial input.
Wow, this project of yours just keeps getting cooler!
-Adam
P.S. I once tried to use sonar as an offensive weapon in a maze solving competition. The mazes had two separated but symmetric areas, with rewards scattered on the separating walls, and two teams’ robots raced to gather the rewards. After taking a round of good readings, my team’s robot would blast it’s sonars repeatedly to try to confuse the other team’s sensors. Unfortunately, small ultrasonic sonar doesn’t penetrate corrugated cardboard very well.
thanks adam,
we all are at the stage of gathering all the information needed and designing the project in theoretical base…i was afraid that the ultasonic would have a kind of weak spot but it is avoidable…i always wandered why use ultrasonic instead of ir…in some degree i still do…it has to do with the type of output and the area of scanning in proportion to the price i guess…
during my search about ultrasonics i ended in the model you propose…(not the same but most characteristics match!)
a bit “dirty” but very cool your misguidance trick at the maze contest 
i am kind of thinking you as part of our team considering the responsibility,speed and spirit of being helpful you show on your replies (taking all the courage,as we do not know each other but a very little)
the project has just began and the complexity of what we are up to and some new subprojects being already proposed,hide many more conversations and ideas!
until next time adam…enjoy