Optical position sensor help!

Thread Starter


Joined Sep 4, 2011
Hi everyone,

I am designing a project that can be used to detect the flight path of an object through a gate. The gate is about 30cm X 30cm and the object is about the size of a small pebble or marble.

This is the approach I was thinking of:

The gate will have optical sensors (IR?), a row of transmittors and receivers along the perimeter and will make up a grid of beams. When the object passes through and breaks the beams, I will be able to tell the coordinates of the grid the object passes through.

I tried using the TIL38 and 81 IR transmitter receiver pair but they are effective up to maybe 5-10cm at most. Does anyone have a better approach or any hardware to recommend?



Joined Apr 2, 2009

Why don't you trying PWM the IR beam. This way u will get plenty of distance and of course you can use multiple IR leds to increase further

John P

Joined Oct 14, 2008
Unless you use lasers or some fancy lenses/baffles, you'll have to use a pulsed scheme to drive the LEDs and read the sensors, because each sensor will be able to see light from more than one LED, and how else can you differentiate them?

So if the LEDs will be pulsed, they will be "off" some of the time, in fact most of the time. So then the question is, how fast is the object traveling? You'll need the LEDs to pulse fast enough, or your object to travel slow enough, that it won't be able to pass through while any given LED is in its "off" state.

If the target object has a size of 1cm and the gate is 30cm square, you need at least 60 LEDs/sensors (30 each for vertical and horizontal) and I'm not sure even that's enough. You'd have to play with a grid of sensors and see if you can get the object through without breaking a light beam. Anyway, it's a lot of components.

This is not a trivial project at all. Could you consider some way to do it using video cameras?