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Topic: Wide ping sensor? (Read 559 times) previous topic - next topic

warren631

Oct 10, 2013, 04:29 pm Last Edit: Oct 10, 2013, 04:36 pm by warren631 Reason: 1
I want to detect objects in front of my robot.  Is there a wide ping sensor?  The normal sensor covers only 15 degrees.  I want about 120 degrees.  I can mount the sensor on a scanner servo but it would have to be sweeping constantly and probably wear out the mechanical servo quickly.   I could use an array of sensors but I only have 3 spare pins on my Uno.   Has anyone tried using an array of ping sensors wired kind of in parallel on one or two pins and just measuring the first echo to arrive (nearest object) (all sensors are triggered together and we just measure the leading edge of all the echos)?  

jremington

#1
Oct 10, 2013, 06:07 pm Last Edit: Oct 10, 2013, 06:10 pm by jremington Reason: 1
Putting digital-output sensors in parallel could be done with a little external logic circuitry, but you would likely want to know which sensor responded first. That is not so simple.

warren631

I don't care which is first, just that there is an obstruction and the robot should stop, backup, turn about 90 degrees and then continue forward.  Its a mower robot with a random pattern (eventually cuts all the grass).

jremington

#3
Oct 10, 2013, 10:48 pm Last Edit: Oct 11, 2013, 04:50 am by jremington Reason: 1
Then use digital-output ping sensors and connect all the outputs to the inputs of an OR gate. The gate details will naturally depend on the type and number of sensors, but with a CMOS 4071 two-input OR gate, the output will go high as soon as either input goes high.

This sounds like a potentially very dangerous project. If the mower is gasoline powered, keep in mind that the spark circuitry radiates interference that is extremely hard on electronics, to the point of component destruction. Other sorts of interference can easily confuse or disable ultrasonic ranging sensors. I hope there won't be any kids or animals playing around the area to be mowed.

joe mcd

Quote
I can mount the sensor on a scanner servo but it would have to be sweeping constantly and probably wear out the mechanical servo quickly.


A Chinese menu of approaches.  Take you pick  :)

(1)You can always use a decent metal gear servo rather than plastic.  The torque requirement is very low so lifespan should be OK.

(2)When using multiple sensors determining which one is easy.  You can only fire one sensor at a time to avoid cross talk.  As a result you know the source of the return signal even if the returns are OR'ed.

(3) Consider using a shift register to 'recover' other IO pins, thus making more available for Ultrasound.


pegwatcher

How about just removing or shortening the little barrels that are there to focus the sound into a 15 degree beam?
I'm not a complete idiot. Some parts are missing.

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