Ultrasonic Interference

Hey, 2 HC SR04 ultrasonic sensors will apparently interfere with each other because they operate on the same frequency. And from what I've read you cant change the frequency, is there a commercially available sensor in which the frequency can be modified? I know that you offset the time of the receiver and transceiver but because for my purposes I will have way too may ultrasonic sensors the delays would be too great.

Thanks Josiah

No, you cannot change the frequency. You can use sensors with different frequencies though. (25k , 40k, 100k,175k,200k...etc)

You could also some modulation techniques but the effort would be high in comparison with the above suggestion.

Thanks for the reply, ok thats a real shame, in this project there would be probably 100 ultrasonic sensors therefore I dont believe that there are enough sensor frequencies. I can't believe that there are no sensors available that let you change the frequency, I feel that would be a standard feature. By modulation do you mean like multiplexing and demux?

http://en.wikipedia.org/wiki/Multiplexing

Thanks, Josiah

Hey, I was browsing the internet when I realized that cellphones change their frequencies all the time, what type of transmitter is that? and can you control it with the arduino? also, this is somewhat unrealated but according to this post, all cellphone towers use a control frequency, if you were to buy an ultrasonic sensor with that same frequency, couldnt you jamm all the cellphones in the area? isnt that too easy?

"this post"= http://electronics.howstuffworks.com/cell-phone3.htm

ps. I know this is an old post, I might post a new thread instead.

So did you found any solution when working with multiple Ultrasonic Sensors. I have a similar requirement where I need to use 400+ sensors and still trying to investigate what all issue I may face when deployed in production. I tried to look for information on the datasheet if any information is given in terms of Signal strength etc to activate the sensor but couldnt find any article.

Share me your inputs how you dealt with this. Thanks in advance!..

sujeet_ssv: I need to use 400+ sensors and still trying to investigate what all issue I may face when deployed in production.

What are you building??

(and if you have a question about your own project, better start a new thread rather than resurrecting a 3 year old one).

If you have 400 distance sensors so closely spaced that the ultrasonics will interfere, then you're using the wrong kind of sensor. Laser or proximity (inductive) sensors may be better. What's it for?

sujeet_ssv: So did you found any solution when working with multiple Ultrasonic Sensors. I have a similar requirement where I need to use 400+ sensors and still trying to investigate what all issue I may face when deployed in production. I tried to look for information on the datasheet if any information is given in terms of Signal strength etc to activate the sensor but couldnt find any article.

Share me your inputs how you dealt with this. Thanks in advance!..

Ultrasonic transducers are resonant speaker/microphones, but the resonant Q isn't that high that you could have 400 different frequencies - that would involve extreme manufacturing tolerances anyway, making things very expensive per sensor.

The best approach is to multiplex in the time domain, allowing enough time between each transducer operating and the next. Clearly this takes time, and synchronization.

A good transducer will have the output given in dB for a given input voltage. Similarly the sensitivity.

Thanks guys for your feedback. BTW I am working on a project to build Parking availability Solution. This is sort of micro architecture based design.

With a wifi controller I am planning pair 4-6 sensors which in turn would send the parking availability information to cloud service. I am looking refresh rate of around 120 seconds interval which is not very aggressive. Also I can time each of the wifi controller from cloud service to avoid interference to some extent.

I tried to search for the stats around lifespan of HC SR04 sensors , How robust it is to environmental conditions etc but didn't found any good article.

I tried to search for the stats around lifespan of HC SR04 sensors , How robust it is to environmental conditions etc but didn't found any good article.

Try Murata

Induction loops at the parking spots sounds like a more robust solution to me. But harder to construct.