pixel data from PC to laser? for PWM greyscale engraving

[alsetn]

Is there a specific pin on the parallel port that corresponds to an image's density or light/dark value? Can I use that data to modulate the laser?
That would be a lot quicker that Mach3 Z axis output for keeping up with raster burning, especially with a high power/fast laser.

[zax15uk]

I'm not sure if you are asking about an input to the laser, or something else?

If you have a Chinese laser then no, there is not a pin going to the laser that would directly control power.

Mach3 can output PWM (designed for spindle speed control), this can either be input directly to the laser control signal on the laser board or converted to an analog voltage with something like a digispeed and used to modulate the laser power.

Either way you are bypassing the existing control board for the machine and would need to replace it with a generic 2-axis stepper driver board.


Sorry if I misunderstood the question, please re-phrase it and I'll give it another shot.

Zax.

[LuAn]

Originally Posted by alsetn Is there a specific pin on the parallel port that corresponds to an image's density or light/dark value?

Think about it. Each pin is a binary output. It's on of off.

A single pin can be pulsed on an off to give a PWM output which may then be 'interpreted' or rectified to give an analogue value. But under normal circumstances i.e. when sending output to a printer, a grey scale value would be transmitted as a byte of data using multiple pins. That's the whole point of a parallel, as opposed to serial, port: it can transmit more than one bit at a time.

[alsetn]

Thanks for your replies. I should clarify my situation. I have a Synrad 125W laser that will be feeding a home made table. Corel or other programs can replicate the drawing through the motors to the workpiece. For vector cutting no problem so far.
If I want to use the high power and speed of the laser for gray scale raster engraving, the beam has to be modulated at a high enough rate to keep up with the traverse speed or the beam. There are pricey boards that can do this but I only need to add the PWM function to my own setup.
Since the pixel depth or darkness value is already being sent to a graphics printer, why not use that high speed data stream to convert to PWM for the beam? The 3 to 5 khz needed is slower than the z axis function of Mach3 can handle. Maybe other output software?
Is there a dedicated PWM output board for this and specifically where (pinout diagram?) would it be getting its data from?
Thanks, Dan

[LuAn]

Originally Posted by alsetn Corel or other programs can replicate the drawing through the motors to the workpiece.

Originally Posted by alsetn Since the pixel depth or darkness value is already being sent to a graphics printer

I think you're getting mixed up between two modes of operation.

When something like a plotter is drawing a vector image the data being sent is telling it to move from one coordinate to another. It's usually using something like a pen which is either up, or down.

When an inkjet, or similar printer is printing a raster image the XY movement is already predetermined i.e. it's going to move from left to right and from top to bottom. For each pixel it receives data telling it what colour the dot should be.

If you're thinking in terms of a parallel port being used with a breakout board (and I think you are) then you're thinking in terms of each pin having a specific function with respect to something on the machine. However when a computer is being used with a printer the pins are being used to send byes of data. In the case of a plotter those bytes of data contain instructions about where it should more, and for a raster printer they contain data about what colours/tones should be printed for each pixel.