Infrared sensor...receiver

[emayank]

I'm a student of B.Tech Petroleum Engg. having no part of electronics in our syllabus. But for my interest I used to study it, and now I'm doing a junior project where I have to work with a microcontroller. The biggest problem that I'm facing is that i dont know how to get voltage output from IR receiver. Actually I require a circuit and its explanation so that i would be able to obtain scaled voltage for different distances. I'll be highly obliged getting your help.

Regards
Mayank Joshi.

[Sparks333]

Hmmm... Scaled voltages for different distances? That sounds like an IR detector circuit, one without automatic gain control... I'll try to find a circuit that might fit your needs.

Sparks

Later: I looked around a bit. I think the component you want is called a phototransistor, or perhaps a photodiode. Both do largely the same thing, except a phototransistor can be biased. Basically, the more IR these things encounter, the more voltage is let through. The circuit itself really depends on what component you choose, as well as one other thing: does your microcontroller have analog-to-digital inputs? If not, then other workarounds are available, but it adds complexity. In choosing your component, keep in mind the amount of current and voltage it will encounter (look at your microcontroller datasheets for these) as well as how wide an angle you want it to see and the wavelength of the IR signal (If you don't have one already, I am betting it's around 950nm. That's a pretty common one.) Be sure that the component you get also does not respond to visible light.

Tell me what happens!

Sparks

[Al Skierkiewicz]

Originally Posted by emayank

I'm a student of B.Tech Petroleum Engg. having no part of electronics in our syllabus. But for my interest I used to study it, and now I'm doing a junior project where I have to work with a microcontroller. The biggest problem that I'm facing is that i dont know how to get voltage output from IR receiver. Actually I require a circuit and its explanation so that i would be able to obtain scaled voltage for different distances. I'll be highly obliged getting your help.

Regards
Mayank Joshi.

Mayank,
What you are asking for has so many variables it cannot be used effectively for distance measurement. A simple IR transmitter and receiver will have very little change in light output over short distances but other factors such as the temperature of the medium, pollution, cigarette smoke, human breath, will all affect the actual receive level. You can use IR with either two transmitters or two receivers in a method known as triangulation. This is where the distance between two devices is known and fixed and the distance to the third device can be calculated from the known distance and the angles. In this particular application, a modulated beam is best so that other IR sources do not interfere. For short distances there is some rangefinders available from Digikey. These devices will give an output for the distance to an object by looking at the reflected energy (from an onboard transmiter). They only measure about 120 cm max though. You didn't specify your distance so I don't know if this will help. Modern video cameras use a version of this method to focus the lens.
Laser pointers can be used in the same application for longer distances. Ultrasonics can be used for distance up to about 30 feet. Although the transducers get a little pricey, they are available and accurate. Kodak developed the technology for their cameras to auto focus.

[Sparks333]

What exactly is this for, anyway? Al is right (as usual) about its inaccuracies.

Sparks