xLCD Backlight Mod
I was annoyed by the fact that you can turn off the chamber light and status bar but not the LCD backlight. So I made a little modification to the display mount to put a switch inside.
What to expect
Display with backlight on
Display with backlight off
Requirements
- My modification of the display mount
- A fitting switch (RUNCCI-YUN 12mm DS-425A)
- Soldering iron
- Wires
- Shrink tubing
- A bit of courage
How to
- Disassemble the display.
- Insert the switch into the printed display mount and connect wires (make sure to have a bit of wiggle room).
- Find the resistor R8 which is connected to PIN 2 of the display ribbon cable (highlighted in green).
- Desolder and solder the resistor so that only the pad connected to PIN 2 of the display ribbon cable is connected. The pad highlighted in green is now free and the second connection of the resistor is now attached to nothing and just laying flat on the solder mask (highlighted in red).
- Attach the wires to the free pad (green) and the free connection of the resistor (red).
- Check if it looks like this:
- Assemble everything.
- Happy printing.
I hope this helps someone. If you have any suggestions: Feel free.
RE: xLCD Backlight Mod
Thanks for posting this! I had chimed in with others on a GitHub request for a timeout to dim the display, but I got an email yesterday saying it was closed due to lack of interest! Prusa’s lack of interest, apparently.
MK4S/MMU3
RE: xLCD Backlight Mod
I didn't check the schematics if it's actually possible to control the brightness of the LCD via software. I only looked for the PIN.
https://www.prusa3d.com/downloads/Electronics_drawings/FDM-XL-MKx-xLCD-29.pdf
I really only looked for the backlight PIN. A software solution - if possible - would be better of course. I see there is a LCD-PWM net but I don't get how it's controlled.
RE: xLCD Backlight Mod
That´s great.
Would it be possible to dim the backlight?
I mean to use an additonal resistor to dim it and a switch, to switch between full brightness and dimmed mode.
RE:
That´s great.
Would it be possible to dim the backlight?
I mean to use an additonal resistor to dim it and a switch, to switch between full brightness and dimmed mode.
Unfortunately, not with a simple resistor. LED backlights like these have their brightness controlled by PWM (i.e. flashing it on and off really quickly, adjusting the ratio of the on-time vs off-time for brightness).
The schematic for the xLCD board is atrocious for reading and understanding the circuit (no left to right signal flow, sub-circuits scatter-shot across the schematic, LCD connector specified but not LCD module, etc.). But my guess is, if one could have an external PWM generation circuit (555 circuit with a potentiometer for brightness control?), it looks like removing the zero-ohm resistor R49 would give a place to inject a PWM signal to control +3.3V to LED-A through Q4. (The above mod by @sushi works by disconnecting LED-K from circuit ground, so would be incompatible with my suggestion.) I could be way off though. I could only find the LED-PWM signal two places, one at what looks like a control for Q4, and the other at the LCD ribbon connector. So it looks like the LCD might source the LED-PWM signal?
See my (limited) designs on:
Printables - https://www.printables.com/@Sembazuru
Thingiverse - https://www.thingiverse.com/Sembazuru/designs
RE: xLCD Backlight Mod
That´s great.
Would it be possible to dim the backlight?
I mean to use an additonal resistor to dim it and a switch, to switch between full brightness and dimmed mode.
Unfortunately, not with a simple resistor. LED backlights like these have their brightness controlled by PWM (i.e. flashing it on and off really quickly, adjusting the ratio of the on-time vs off-time for brightness).
The schematic for the xLCD board is atrocious for reading and understanding the circuit (no left to right signal flow, sub-circuits scatter-shot across the schematic, LCD connector specified but not LCD module, etc.). But my guess is, if one could have an external PWM generation circuit (555 circuit with a potentiometer for brightness control?), it looks like removing the zero-ohm resistor R49 would give a place to inject a PWM signal to control +3.3V to LED-A through Q4. (The above mod by @sushi works by disconnecting LED-K from circuit ground, so would be incompatible with my suggestion.) I could be way off though. I could only find the LED-PWM signal two places, one at what looks like a control for Q4, and the other at the LCD ribbon connector. So it looks like the LCD might source the LED-PWM signal?
I wanted to write basically the same but apparently I have to wait for moderation and I wanted to wait for my last post. Anyway. There is enough space for PWM circuit in the case.
It seems I forgot the link to the 3D part in my first post: https://www.printables.com/model/1313876-xlcd-display-mount-backlight-mod
RE: xLCD Backlight Mod
I could be way off though. I could only find the LED-PWM signal two places, one at what looks like a control for Q4, and the other at the LCD ribbon connector. So it looks like the LCD might source the LED-PWM signal?
I had another look at the schematics. I think it is supposed to be like this:
- Populate the component U4 on the PCB
- Change the firmware which uses LCD-CS and address the newly added U4 red channel to set the wanted brightness
I think this is how they planned to do this originally. It seems they wanted to use the 3 LEDs in the LCD assembly as status light and use the "4th" LED to set the brightness of the display.
This change might be actually fairly easy and as funny side effect you could use the 3 currently unused LEDs in the display assembly.
I wanted to edit my previous post but I guess I was to late.
RE: xLCD Backlight Mod
I could be way off though. I could only find the LED-PWM signal two places, one at what looks like a control for Q4, and the other at the LCD ribbon connector. So it looks like the LCD might source the LED-PWM signal?
I had another look at the schematics. I think it is supposed to be like this:
- Populate the component U4 on the PCB
- Change the firmware which uses LCD-CS and address the newly added U4 red channel to set the wanted brightness
I think this is how they planned to do this originally. It seems they wanted to use the 3 LEDs in the LCD assembly as status light and use the "4th" LED to set the brightness of the display.
This change might be actually fairly easy and as funny side effect you could use the 3 currently unused LEDs in the display assembly.
I wanted to edit my previous post but I guess I was to late.
Yeah, I saw that U4, WS2811. Looks like the IC version of the control chip inside a WS2812 "NeoPixel". I can see on the product photo of the xLCD assembly that U4 is on the front of the board, just towards the middle of the board from the right-most LED. With a steady hand, one could populate the DNF parts. That whole section of the schematic took me a few minutes to realize that they are the LEDs. Unfortunately, the schematic doesn't tell us what the actual LCD module make and model is to look up the datasheet to know whether the LCD-PWM signal on pin 8 is an input or an output.
Anyone else have a loose xLCD assembly that can look for a part number on the LCD screen and/or its ribbon cable?
As the board is (as long as it matches the schematic) with a bit of firmware hacking one could add a string of NeoPixels to the unpopulated P1 and have more individually addressable lights. The data output of that last LED (or U4 if manually populated) goes to P1-2, and you can tap power and ground for a 5V NeoPixel string from P1-6 and P1-4, respectively.
See my (limited) designs on:
Printables - https://www.printables.com/@Sembazuru
Thingiverse - https://www.thingiverse.com/Sembazuru/designs
RE: xLCD Backlight Mod
I was wondering about why the PWM signal goes into the ribbon cable as well and I actually unplugged the cable but it didn't help me finding out the actual model of the LCD. I would suggest to see what happens if you simply manually put a PWM signal into the PIN. This could be an easier way to reverse engineer what this signal is actually doing than populating the part and modifying the firmware. This can still be done once the function is clear.