LED/"LASER" Printers - How are +5000 LEDs addressed/controlled?

  • Thread starter NTL2009
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  • #1
NTL2009
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I recently re-watched this video:



And I wondered, how are +5000 LEDs addressed/controlled? At 600 x600 DPI and an 8.5"x11" printing area, you need ~ 5120 LEDs across and 6600 scans. At 20 ppm, the scans would need to be less than 3 seconds total ( need to allow time for fusing, etc), so ~ 0.45 ms to "load" 5120 LEDs.

I'm thinking shift registers? One long register would be ~ 87 ns per LED, or ~ 11.377 MHz clock? I'm not sure that speed would be practical across that large an area or not, but it's far less than motherboard speeds. Maybe several (16?) in parallel. With 16 (a convenient digital hardware and software number), the shift registers would only need to be 320 deep, so 1.4 us per LED, or ~ 711 KHz clock? That speed may be more fault tolerant and/or cheaper to implement?

Or a different approach? It just seems like shift registers would be the simplest layout for such a small space (1:1 output with the LEDs, no matrix wiring).

-TIA
 

Answers and Replies

  • #2
Baluncore
Science Advisor
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A LED printer would be easy compared to the significantly faster update of a 4k OLED screen.
 
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  • #3
Tom.G
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Laser printers use a single Laser diode. The horizontal scanning is done with a rotating octagonal (or maybe it hexagonal, don't remember for sure) mirror.

The vertical (length-wise) scanning was just the paper movement thru the printer.

One of the common failure modes in some early, major brand, printers was the IC (chip) that drove the scanner motor. I don't remember the details but the electrical design was rather borderline. I have repaired a few by replaceing the IC in the scanner assembly and adding a few resistors.

The other, less common failure mode, was the bearings wearing out, requiring a motor replacement; but it was more practical to replace the whole scanner assembly.

The service manual for an early (2004) Laser printer is available here:
https://www.printertec.com.br/arquivos_download/1160.pdf
Lots of technical info there!

Have Fun!

Cheers,
Tom
 
  • #4
DaveE
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There are a lot of potential methods for writing data to HW in a uC.
In general, I don't really see that this is any different than writing to RAM as viewed from the uP buss. Memory mapped I/O is one common method in larger uC systems. It doesn't take long for a special purpose uP or FPGA to fill up 5K of RAM.
 

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