by rvdokkum on Sun Mar 31, 2013 11:28 am

Hi adafruit forum

I'm planning to do a project using 20 range finders.
They will be placed to not interefere with each other.
they will be connected to an arduino due the have enough input output pins.
the will have extention cables of 30 feet / 10 meters.
I like to measure distance with each range finder 10 times per second.
I also like to send the measured values over a serial connection to a pc where i will use the measurements in my own software.

i thought of using the ''Parallax PING))) Ultrasonic Distance Sensor ''

i know i have to write a script for the arduino send and receive signals to the sensors and measure the duration to calculate the distance measured.

will the arduino be fast enough to handle all 20 sensors and communicate the measurements over serial to a pc?

is there something i may not overlook?

thanks in progress for advising me.

Remko van Dokkum.
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by adafruit_support_bill on Sun Mar 31, 2013 11:41 am

I would suggest instead using the Maxbotix sensors. They come in various models with different coverage patterns and support direct analog outputs as well as pulse width and digital serial outputs.

They also support "chaining" for continuous sensing using multiple modules without interference between the modules. ... AN_Out.pdf

The biggest issue with either type of sensor is the number of pins available on the Arduino Uno. To effectively handle 20 sensors you will probably need to consider an Arduino Mega.
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by rvdokkum on Sun Mar 31, 2013 12:16 pm

Hi adafruit support

Thanks for suggesting the maxbotix sensor.

Still i like to know if I risk interference/ error / noise when using long lines for VCC GND AN BW. 30 feet / 10 meters?
the RX TX lines in the chain will be 2 meters / 6 feet. and form a big cirkel.

i will then use the analog input pins to receive the measured values.
I can only have 16 analog inputs using the arduino mega. have to skip 4 of the 20 sensors i guess.

so using the maxbotix as chain saves a lot of work for the arduino.
only work left will then be passing on the measurements to a pc over serial communication.

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by adafruit_support_bill on Sun Mar 31, 2013 12:44 pm

I haven't set up any with interconnects of that length. I will see if I can get an opinion from Maxbotix on that.
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by MaxBotix Inc on Mon Apr 01, 2013 9:45 am

Hello! This is Tom Bonar from MaxBotix Inc. I saw your forum post and would like to give some information regarding your application.

In your application you mentioned that you are planning a project with 20 range finders.

The first thing I would like to recommend is use a star topology for your power and ground. In this system setup, each item has its own power and ground running back to the source. If one component has a high current draw, such as a motor, only that component will have it’s voltage reduced. This voltage reduction is due to resistance in the wiring. The item with the high current draw, along with the associated changes to both the power and ground, are isolated from all of the other items being powered. A diagram and full explanation of this can be found in our article entitled "MaxSonar Operation on a Multi-Copter", under a section entitled "Grounding and Power".

In your application you also mentioned the use of cables 10 meters long, as well as an expressed concern about interference.

If you are a using a shielded cable, such as the MB7954, with proper connections you should be able to run cables a long distance with no interference. We have used this cable for stretches up to 1000 feet with no interference.

Finally, you mentioned that you wanted each range finder to measure distance 10 times per second.

If you are chaining the sensors in such as way where each sensor is commanded the next sensor in the sequence to range, each sensor will only range when it is commanded. So in your case, if 20 sensors are used in the chain, each sensor will only range 1 time every 2 seconds. You will still get 10 range readings each second, but each range reading will come from a different sensor in the chain. For information regarding chaining, we have an article entitled "Using Multiple MaxSonar® Sensors Simultaneously".

Does this information help with your application? If you need additional assistance, please don't hesitate to email me.

Please let me know if you have any questions.

Best regards,

Tom Bonar
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of MaxBotix Inc.
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