I am interested in detecting if an object (e.g. small box made of non-conductive material like plastic/acrylic/wood) is placed on top of a surface (e.g., a table), I don't need to identify the object, I just want to know if it is there.

There are various methods to doing this, but I wanted the easiest/cheapest way. I first thought of using a Mini Photocell ($1.50), which is a simple light sensor, however, this will not work if the room is initially dark.

Then I found the Optical Detector / Phototransistor - QRD1114 ($0.95).

  • I believe QRD1114 should work regardless of lighting conditions, since this uses IR?
  • I need to consider the approaching object (e.g., small box) should be able to reflect IR?
  • Any ideas on the IR beam?

The detecting sensor must be very small and cheap.

  • \$\begingroup\$ If the box is going on a table, can you put a pressure sensor on the table instead? \$\endgroup\$ – Greg d'Eon Mar 16 '15 at 16:00
  • \$\begingroup\$ @Gregd'Eon: Interesting idea. The issue is the small box is not really that heavy and my guess would be that it wont exert enough force/pressure for the sensor to detect it? \$\endgroup\$ – lucidgold Mar 16 '15 at 16:01
  • \$\begingroup\$ Check out this answer for a couple of ideas: electronics.stackexchange.com/a/35314/49251 It looks like you can make it quite sensitive. \$\endgroup\$ – Greg d'Eon Mar 16 '15 at 16:02

The QRD1114 will have a very short range, but yes with a IR LED pointed at the spot of the object, depending on the object properties, it will work.

The better thing might be a cheapo sonic sensor like you can find from HobbyKing "Ultrasonic Module HC-SR04" for about $3, which will give you a broader region to detect in, more range, and is also light-invariant.

| improve this answer | |

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.