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

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In summary: Shift registers are a good way to address this. It's a bit more work, but it's less work than writing to RAM. If you need to address more than 5120 LEDs, you'll need to use a matrix.
  • #1
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).

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  • #2
A LED printer would be easy compared to the significantly faster update of a 4k OLED screen.
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  • #3
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:
Lots of technical info there!

Have Fun!

  • #4
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.

1. How do LED/Laser printers work?

LED/Laser printers use a laser beam to scan the surface of a drum inside the printer. The laser beam is then reflected off the drum and onto a charged photosensitive drum, creating an electrostatic image. This image is then transferred onto paper and fused using heat and pressure, creating a printed page.

2. What is the difference between LED and Laser printers?

The main difference between LED and Laser printers is the technology used to create the electrostatic image. LED printers use a light-emitting diode array to create the image, while laser printers use a laser beam. LED printers tend to be smaller and cheaper, while laser printers are more common and often have faster print speeds.

3. How are +5000 LEDs addressed/controlled in LED printers?

In LED printers, each LED is controlled individually by a microchip. The microchip sends signals to each LED, telling it when to turn on and off, and at what intensity. This allows for precise control over the electrostatic image being created, resulting in high-quality prints.

4. Can LED/Laser printers print in color?

Yes, LED/Laser printers can print in color. Color LED/Laser printers use a combination of four toner cartridges (cyan, magenta, yellow, and black) to create a full range of colors. The toner is transferred onto the paper in layers, creating a full-color image.

5. How do LED/Laser printers compare to inkjet printers?

LED/Laser printers tend to have faster print speeds and produce higher-quality prints than inkjet printers. They are also more cost-effective for high-volume printing. However, inkjet printers are typically cheaper upfront and can print on a wider range of paper types and sizes. It ultimately depends on the specific needs of the user.

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