I need a sensor which can count a fast moving object. I am thinking to use IR beam break sensor. But, I think there will be a problem with the sunlight as the Tx-Rx will be 4-5 meters apart.

I also need to consider the fast response time. IR sensor has better response time than LDR. Am I right?


Consider, the fast moving object is like a soccer ball (a bit smaller than a soccer ball, though). Its speed is between 15ft/s - 60ft/s.

  • \$\begingroup\$ LDR has a bandwidth of about 8Khz so it's about as fast as an IR sensor inteded for remote-control applications. an IRDA receiver may be faster. \$\endgroup\$ – Jasen Jan 9 '17 at 5:45
  • \$\begingroup\$ "a fast moving object" How fast ,how big? A golf ball sized object travelling at 1000 km/hr is not the same problem as a person travelling at 10km/hr. \$\endgroup\$ – JIm Dearden Jan 9 '17 at 13:32
  • \$\begingroup\$ @JImDearden Consider a soccer ball size object. It's traveling at 15 ft/sec-60 ft/sec. \$\endgroup\$ – Mat_python Jan 9 '17 at 16:27
  • \$\begingroup\$ @Jasen I am considering response time. I want response time in us, ns, or less than 1 ms. I found out that IR receivers have faster response time than LDR. Can you share the link for IRDA? \$\endgroup\$ – Mat_python Jan 9 '17 at 16:30
  • \$\begingroup\$ en.wikipedia.org/wiki/Infrared_Data_Association \$\endgroup\$ – Jasen Jan 9 '17 at 21:49

The best ways to make a light beam system work reliably in uncontrolled lighting conditions is to look at these two things:

  1. Try to arrange the receiver to have a tubular aperture in front of the detector that is aimed right at the transmitter. This will help the receiver to be much less affected by light reflections and outside sources.
  2. Modulate the transmit beam by some scheme, either by a protocol or a validity window. Then make the receiving detector look of the protocol to know that the beam is present and valid. Obviously the data rate of the modulation needs to be higher than the object detect rate.
  • \$\begingroup\$ It helps immensely to use a thin film narrow band optical filter, as well. And in this circumstance, crystal controlled narrow band modulation with a very narrow acceptance band on the receiver. \$\endgroup\$ – jonk Jan 9 '17 at 7:55
  • \$\begingroup\$ @jonk Can you share the link for a thin film narrow band optical filter? \$\endgroup\$ – Mat_python Jan 9 '17 at 16:31
  • \$\begingroup\$ Thank you, Michael. What scheme would you suggest for this? Did you mean something like TSOP sensors? I just updated my questions with the speed of an object. \$\endgroup\$ – Mat_python Jan 9 '17 at 16:33
  • \$\begingroup\$ @Mat_python I'd rather create an answer, then. There's more to the process than just referring you to a filter. I'd need to know what your physical design will be and what you are dealing with in terms of the ambient environment (direct sun? window area to be observed, etc.) That's why I didn't offer an answer. I just don't know enough about your circumstances since you haven't described them very well. (I can even imagine the use of a spatial filter, too.) \$\endgroup\$ – jonk Jan 9 '17 at 19:09
  • \$\begingroup\$ @jonk Sure. My primary goal is to detect the moving object. I don't care what size of the sensor I use, as of now. I thought of using 40 IR LEDs as a beam transmitter on one side. Another side, there could be some IR Receivers. Let's say, 5 IR receivers are placed vertically. Thus, the dimension of the array would be IR Receivers (i.e, 5mm x 5 = 25 mm) + Space between them (i.e, 5mm x 4 = 20 mm) = 45 mm. This is the first time I am working on this kind of project. Find the speed range in the question. \$\endgroup\$ – Mat_python Jan 9 '17 at 20:04

To tolerate sunlight, use a phototransistor (responses often 1uS or so), and run 1MegOhm resistor from collector to base, with 10KOhm from collector to +5v.

You'll notice the collector voltage tends to remain stable, near VDD/2. If not near VDD/2, adjust the Base up or down.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.