[SOLVED] Laser distance measurement components

[stephkre]

Hello,

I have a project that I want to do using lasers to detect a persons shoulder from no more than 3 meters away and no less than 2 meters away. I have looked at other detection solutions such as IR and other devices but due to the material type (t-shirt) and the device having to work out side I have ruled those out. Unless you think it can still be done.

Also, I don't want a full solution laser detection module like keyence makes but more of just the sensor and the pcb board. I will have a housing designed for my project. Is there a board out there that will give me the capability to do this? I wanted to ask before having to design my own board. Also what is a price range of such a device compared to buying one and making one myself? The laser needs to be a class I laser and have multiple detection zones. If so can I also get documents to learn more on building a laser distance device?


Thanks,

Stephen

 

[sky_123]

I'm not really an expert on it, but generating pulses and detecting time for laser bounce is quite hard I think, which is why the laser distance measurers cost so much.
You'd need to be able to resolve a time period of the order of nanoseconds or less I think, for a decent resolution.

There is an alternative method, which uses the idea of shining a laser spot, and observing it with a camera which is offset from the laser by a known separation. By looking at where
the laser point is as viewed by the camera (it will be the brightest spot on the image), and using trigonometry, you can work out the distance. It is quite popular with the
robot experimenters community.

If you wanted to do it the first way, then the cheapest method would be to use an existing laser distance meter, and hack it. Or you could try to purchase a module but it may be
hard to find. I think Leica make most of the modules in commercial laser distance meters (even third party ones possibly).

If you just want an approximation if something is present 2-3 meters away or not, then some other technology may be cheaper, e.g. ultrasound maybe, or PIR if they are moving.
Depends on your application. Lots of experimentation will be needed regardless of the method chosen I guess.

 

[stephkre]

I will look into the existing laser distance meters to see if I can get any more data on it. In the mean time is there any place I can look to find cameras and documentation using the way your talking about doing which I would expect to be cheaper. The application needs to be accurate enough to a inch or so. I like the idea of the camera but I dont know how accurate that would be.

 

[sky_123]

There are lots of low cost camera modules, e.g. https://www.sparkfun.com/products/8667 but I don't have a link to the procedure. A google search will reveal more info on it, but I don't
think it is anywhere near as accurate as you want it.
I might be wrong, but I don't think any method will give you 1-inch accuracy at 2 meters away, unless you use a real laser distance meter. And bear in mind that even those usually
don't like the object to be moving much, otherwise they report a 'try again' warning rather than report an approximate distance. They go by the philosophy that if they're not sure,
then they won't report a value.