28 Jun
2010
28 Jun
'10
12:31 p.m.
Hi guys,
I've got a Laserjet III laser scanner module kicking around in my
junkbox, harvested from an utterly screwed LJ3. It has a fibre-optic
light pipe on one side, which connects to a photosensor on the
motherboard. Does anyone know what the frequency or period of the
photocell signal is?
I don't know off the top of my head, but it should be farily easy to
measure the speed of rotation of the motor. Each revolution would
generate <n> beam detect pulses (the output of the photosensor) where <n>
is the number of sides of the polygonal mirror.
Note that the beam detect sensor detects light from the actual laser,
there is no other light source. At the end of each line, the laser is
turned on, the formatter then waits for a pulse on the beam detect line.
Of course at the start of a page, the laser it turned on until the
controlling electronics starts to get beam detect pulses, so it knows
roughly when to ecxpect them thereafter (and can then know when to turn
on the laser for this purpose).
-tony