What kind of sensor could you use to detect the shape of a shadow falling on something, say the shadow of a hand on a wall?

I first thought of an array of LDRs but the resolution would be quite low, and you would need quite a lot of them. Or is this feasible?

Then I thought of a camera with image recognition software, but the problem is that the object causing the shadow would get in the way of the camera's view. Unless maybe the camera was at an extreme angle.

Is there any obvious solution for this?

EDIT: Sorry, yes it is not necessarily an analog sensor so I have adjusted the title. The application is to use different shadow shapes to control a robot, as an interface.

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    \$\begingroup\$ Maybe provide some more details about your application? I would say the camera is probably the best choice for most applications, but hard to say for sure without knowing your end goal. \$\endgroup\$
    – Selvek
    Jun 4, 2018 at 3:12
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    \$\begingroup\$ I agree with @Selvek. A camera will probably be your best bet, but that's very hard to judge without knowing your goal and what you're connecting it to. It's also a little confusing having "(analog)" as a specification since most cameras are going to have a digital interface or at least need some level of digital processing if you're looking to do image recognition. \$\endgroup\$
    – Phil C
    Jun 4, 2018 at 3:56
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    \$\begingroup\$ You will need a light sensitive camera, designed with large pixels and/or a long shutter time option. The camera need not have many pixels if your only concerned about one small area. Scour the Pawn Shops for older cameras. \$\endgroup\$
    – user105652
    Jun 4, 2018 at 4:04
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    \$\begingroup\$ If you are afraid the object that causes the shadow is in the way, you might have to use multiple cameras at different angles and use the camera which has a 'clear' view. \$\endgroup\$ Jun 4, 2018 at 8:19

1 Answer 1


Instead of a light source and casting a shadow on the wall, just put the camera where the light source would be and develop a filter to differentiate blank wall form the intervening object, hand, or whatever would cast the shadow.

With a little care you can probably also have a light source co-located with the camera, if you want to still cast a shadow for the benefit of observers at other vantage points.


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