Line scan Camera..

memooo2006

Hi there, I have posted a thread before asking about this sensor and you guys helped me a lot. and I have actually used it in a project and it was satisfactory. The project was a guide path follower you can see the robot in the following link if you are interested.

http://www.youtube.com/watch?v=v1rozQMu-vQ

Now I am trying to use the same sensor building a project called electromagnetic levitation. The problem I am facing right now is the speed of the sensor. In my guide path followe project I was scannign at an intergration time of 35 mS because I could not go faster than that.

So I guess my question is: How can I scan at much faster speed like in MicroSeconds.

Thanks A lot for your help. and please let me know if there is any thing I did not explained properly.

Regards..

Mike Green

The line scan sensor has an exposure time, just like a piece of film. The shortest exposure is about 250 microseconds. Like any piece of film, at shorter exposures, you need more light intensity to get a good image. In addition to that, the sensor has to be scanned one pixel at a time and the output of the scan is analog information which has to be converted to digital form, then read by the Stamp or Propeller or whatever. All of this takes time. To scan at faster speeds, you need a more sensitive sensor capable of higher speeds. You need a faster analog to digital converter, and you need a faster microcontroller (like the Propeller) as well as devoting a lot more I/O pins to the task (to increase the speed of data transfer).

Note that you could use the bare TAOS sensor along with a high speed analog to digital converter and something like the Propeller to get a scan rate of one line per 34us or so ... very very difficult to get that sort of speed.

For your application, you might just need a couple of IR LEDs and phototransistors

memooo2006

Mike,

Thanks for your reply. I just don't know what do you mean by bare TAOS sensor, which one do you mean? Also I will consider having high intensity lighting source and using fast microprocessor. I have looked into Propeller and I really liked how fast it can go,80 MHz. But the thing is, I only worked with C language and I am not sure if Propeller would support that.

Last thing, would you please give me some examples of photosensors that I might use. coz I might consider that if i see that the Line Scan camera is hard to use.

Thanks alot for your help.

Memooo

Mike Green

The line scan sensor sold by Parallax consists of the TAOS sensor plus a microcontroller and a voltage regulator. By "bare TAOS sensor", I'm referring to only the TAOS sensor without the other components.

There is a 3rd party free C compiler for the Propeller (Catalina). The code it produces is not as fast as Propeller assembly language, but there are other advantages to its use.

Look up "phototransistor" in the Wikipedia. Without a lot of information from you about what you want to sense and how it's laid out physically, it's hard to give you examples. Pretty much anything you'd do would consist of an LED and a phototransistor in some kind of mechanical / optical arrangement so that the light beam shines on the phototransistor. Sometimes there's an object that blocks the light and the phototransistor detects that. Sometimes there's an object that blocks the light and occasionally there's an opening that the light shines through and that's what's detected. You can also have a reflector that sometimes allows the light to shine on the phototransistor. Look in a Jameco or Mouser on-line catalog at the datasheets for optical sensors and you'll get some idea of what's available.

Phil Pilgrim (PhiPi)

One minor correction to Mike's post: The TSL1401-DB module does not come with a microcontroller or regulator. Those are provided by the boards it plugs into: the MoBoStamp-pe (with firmware for the AVR) and the Propeller Backpack. (It also plugs into the Spinneret, but the Prop on that board is not configured with delta-sigma ADC circuitry.)

So it is possible with the TSL1401-DB to interface directly with the TAOS sensor, albeit without the advantages of the AVR and Propeller drivers already written for it. For maximum speed, as Mike correctly points out, a fast, dedicated ADC chip would be advantageous.

You might also consider connecting its analog output signal to a simple logic input, such as a Prop pin. In the case of high-contrast subjects, such as a backlit metal ball, this one-bit comparator-equivalent input will be the absolute fastest way to obtain useful position data from the TSL1401.

-Phil