One-dimensional velocity sensor

Hi all,

I am taking part in a project involving teams who are designing electronic components to be used in a small racing car. Our task is to design and build an optical speed sensor, which has to measure the absolute speed of the car relative to the ground. We researched optical mouse sensors, and understand the basic principle: a camera takes 'pictures' of the surface, which are then brought into a microcontroller where analysis on individual pixels is performed. A speed can then be calculated in the software, by observing the time taken for a pixel to 'move' from one area of an image to a different area of a new image.

Of course, with mouse sensors and computers, two dimensions are being measured. For our purposes, we find it suitable to only measure across one dimension. I was wondering if anyone on this forum has had any experience with this sort of technology. A mouse sensor takes roughly 1500 of these pictures a second, which might not give a high enough sampling rate to accurately measure up to 100 miles per hour. Is there a better way to do this, perhaps only using one dimension? We are also finding it difficult to research how exactly the software reads in the data from the camera, and how it can identify a lighter or darker pixel based on the pixels around it. There doesn't seem to be enough information on the web about that in particular.

Any help in getting us pointed in the right direction would be greatly appreciated!

Mark.

 

Thanks Harald. We actually looked into this doppler radar method, but the racing team are wanting us to use a purely optical sensing method. Apologies, I forgot to mention this in my post.

Thanks Steve. We could use a lens under the sensor to focus in on a smaller area. And we would use a high power red LED together with a different lens to illuminate the surface area which the sensor would be placed above. The problem of outside light interference would be minimal I believe, given that the this setup would be placed on the middle of the underside of the car.

The racing team have had groups try with the optical mouse before, and they've got close, but not close enough. They are encouraging us to look for an alternative optical method, but like I said, it's the hardware to software stage of 'reading in' the surface data which has us a bit lost.

 

Thanks guys. The 5th wheel is a great idea, which I hadn't thought about. I've got good experience with phototransistors and infrared LEDs for light detection from other projects. If we come to a dead-end with this optical sensing method, it would be a good thing to fall back on.

Doing more research on the processing of pixels in an image, autocorrelation seems to crop up a lot. Most examples, however, are based on the processing of periodic signals (for example, pitch detection in audio analysis). I'm not sure how similar or different the algorithms would be for pixelated image detection.