[Ronja] TX Head design question...

[Gyurkó Martin]

Hi!

in the early years, when Laser printers were born they had a quarz 
crystal, in which acustic wawes were induced. these wawes acted as a 
diffraction pattern to the laser, and this diffraction was steering the 
laser on different points on the paper, or was switching the laser when 
the LD was too slow.
This is only working cool if the light is monocromatic.
LEDs are unfortunately not.
Also these crystals are extremely expensive.

But if you are good, then you can use a DVD, focus a beam on it, and 
steer the reflected light to the TX lens. This would work like a shutter :D
But you would need servo control of the head, which is not that easy.


bye,
Martin

J.D. Bakker írta:
>> Hi All,
>>    Just a quick question - Is there any reason why instead of forcing
>> the TX led to produce the pulses, a "shutter" cannot be employed instead ?
> 
> No fundamental reason, just practical ones. Sourcing shutter 
> film/foil which can reliably switch at 10MHz is likely challenging, 
> especially in the small quantities that the average Ronja builder 
> would need. Common LCD shutters max out at 100Hz-1kHz, so we'd need 
> four to five orders of magnitude better performance. If the shutter 
> were placed between LED and lens viewing angle and diffraction must 
> be accounted for, if the shutter is placed after the lens it needs to 
> be physically large (and diffraction is still an issue).
> 
> More here:
> 
> http://www.liquidcrystaltechnologies.com/tech_support/LCDShutterConsiderations.htm
> 
> Have you any suggestions for such a shutter?
> 
> JDB.