Continue to Site

# How does the CCD Array in the sharp GP2D12 infrared sensor calculate angles/distance?

Status
Not open for further replies.

#### fantabulous68

##### Member
This is what i know:

If the surface of the liquid/object is within range and in line with the IR beam, reflected light forms an image on a linear CCD array in the receiver.

Can someone give me a more in depth explanation, or relevant links would be useful too.

lol is that question hard? My examiner asked me that at my presentation yesterday

I said it uses Triangulation, but he wanted to know how

Last edited:
Look thru this link.

Sharp GP2D12

I have that link already and lol it doesn't even mention the word ccd array.

Try ctrl+f ccd or ctrl+f array

But thanks for tryingMr Gibbs

Ok with google i found this info:
This sensor works by sending a pulse of IR light through its emitter. If the light hits an object it is reflected back, creating a triangle between the send, receive, and reflection point. The emitter for this sensor is a precision lens that reflects light onto a small linear CCD array. The way the light falls on the CCD array makes it possible to calculate the distance from the object.

• The GP2D12 uses an IR emitter and a small linear CCD array detector that is 3/4" away from the IR emitter, in order to calculate the distance an object is away from the sensor. It can detect distances that are around 4" to 30" away from the sensor. The IR emitted sends off some IR light and the light will be picked up by the detector. Between the IR emitter, the point of reflection at the object the light hits, and then the detector, a triangle is formed and from this the distance can be calculated. The angles in this triangle will change depending on the distance of the object and thus we can calculate the distances using the angles.

but i want a more in depth explanation, somebody, anybody,
im gonna try wikipaedia now

Last edited:
I have that link already and lol it doesn't even mention the word ccd array.

Try ctrl+f ccd or ctrl+f array

Wooo Ms F that smarts!!
The optics dont form a true image on the CCD just an illuminated area offset at an angle from the source.
The GP2D12 outputs a signal proportional to this offset which is related to the angle.

Using fairly simple trig from these angles a range/distance can be calculated.

Last edited:
Wooo Ms F that smarts!!
lol is that sarcasm
Thanx Mr Gibbs, thats a good explanation. I have a better understanding now.
WIKIPAEDIA:
A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time. Technically, CCDs are implemented as shift registers that move charge between capacative bins in the device, with the shift allowing for the transfer of charge between bins.

Often the device is integrated with a sensor, such as a photoelectric device to produce the charge that is being read, thus making the CCD a major technology where the conversion of images into a digital signal is required. Although CCDs are not the only technology to allow for light detection, CCDs are widely used in professional, medical, and scientific applications where high-quality image data is required.

A CCD is an analog device. When light strikes the chip it is held as a small electrical charge in each photo sensor. The charges are converted to voltage one pixel at a time as they are read from the chip. Additional circuitry in the camera converts the voltage into digital information.

#### Attachments

• ccd.JPG
37.7 KB · Views: 3,872
Last edited:
That's not a bad picture. They've even got the trasmitted beam at 90' (which is correct) lots of the pictures you see for the sharp sensors get that bit wrong.

If the transmitted beam is at 90',well, when it meets a perfect plane surface, as the picture shows it, how can it be reflected with an angle different from 0?

Who said the plane surface was perfect?

Oh yes, you are right, I have forgotten that. But, if the surface is a plane mirror, well, does it mean that the captor can't calculate the distance?

Last edited:
Hello, i'm Luigi from Italy and i just registered in this really helpful forum and this my first post. I know this is an old thread but i would like to give this link to everyone facing with the same problem and as, with your forum, you helped me with different issues I faced with . i found out this link as i'm trying to understand how different materials (therefore different refraction coefficients) will affect my underwater application and measurements, this explanation seems good to me (at least, as i'm a mechanical engineer, it seems to be good for my mathematical background). what they are trying to do is to create a sort of range finder using a webcam and a laser, using the webcam as a ccd array.

Last edited:
Hi Luigi, interesting link, and that is a common way people are making range finders from a laser and camera.

Check out; **broken link removed**

They are using a laser line, camera and some Windows software to accurately scan 3D models, down to a very fine "distance" reading. It's pretty cool.

Hi, I already knew this scan cause my field is in product development so I'm more focused on cad, reverse engineering and rapid prototyping but i didn't now this, let's say, DIY laserscan was based on the same principle

Yeah the principle is easy, but it requires some complex image processing. With that "David" system they use PC software for the image processing and modern PCs have a huge processing ability.

If you just use a laser dot and a camera (and only need a single distance measurement) the processing gets a lot easier! I would just build it and measure it underwater and make a compensation curve in a lookup table.

Last edited:
Light is also reflected by the edge of a mirror - not it's surface.

If the object is within measuring range (4 to 30cm) you'll get a usable return signal.

One of the applications is the use for automatic pissoir flushing systems.

If the "echo" caused by clothes is strong enough for measurement a solid mirror edge will be, too.

Boncuk

Yeah the Sharp sensors will actually detect clear glass too, it's a bit of a problem. The datasheet says something about glass having to be very close to the sensor (under it's minimum range) to avoid issues.

I did some experiments here on the forum a couple years back testing the Sharp sensors to see the top surface of clear water, it was touch and go. They will return a reading from a clear surface.

Last edited:
Status
Not open for further replies.