# Proximity sensor with LDR

1. Homework Statement

I am just about to start my AS level Advancing physics - Sensors coursework.

I was wondering whether it would be a good idea to build a proximity sensor using an LDR in a potential divider.

I would reflect an LED off an object, and move the object at different distances away from the LDR.

I would take readings of the voltage across the potential divider output with the object at these different positions, and plot/analyse graphs of distance against voltage.

Would this be a good idea? Or would I get a series of inaccurate and unreliable results?

2. Homework Equations

3. The Attempt at a Solution

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mda
There are two issues here:
- the amount reflected back to the LDR will also depend on the particulars of the object (meaning you can't accurately determine distance for an arbitrary object)
- background noise... there are some simple ways to get around this that I can tell you if you want.

If you are serious about measuring distance I would suggest ultrasound. It is also possible to do this with light but short distances are very difficult due to the high speed of light.

could I get rid of the first issue by using an LED to replace the object?

Wouldn't doing the experiment in a dark room fix the noise problem?

If not, how would I do an ultrasound sensor? I'm not really very familiar with them.

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mda
could I get rid of the first issue by using an LED to replace the object?

Wouldn't doing the experiment in a dark room fix the noise problem?

If not, how would I do an ultrasound sensor? I'm not really very familiar with them.
To a certain extent an LED object will "fix" the first problem but you'll need to keep the orientation constant. And yes, a dark room will get rid of most of the noise. But this isn't really a realistic situation is it? Depends what your main goal is I suppose.

The idea with the ultrasound is to make a sonar... send pulses through the transducer and measure the time delay. It will be more complicated than your LDR system.