5 ms·

Driving TFEL LCD Panels with RP2040: Offloading the CPU Step by Step

36 points by _Microft 5y ago

1MachineElf 5y ago
I appreciate the depth of this guide. The display is gorgeous. Why aren't these more common?
- mastax 5y ago
  Expensive (this one is $700+), monochrome, fragile, dim, burn-in, high-voltage.
  - prvc 5y ago
    Why so costly?
    - flaviut 5y ago
      Pretty much answered by the original question: > Why aren't these more common? There's no economies of scale. Looking at the ad for these in https://www.lumineq.com/technology https://www.lumineq.com/technology: "TFEL technology has proven its excellence in applications ranging from monitor and control instruments in deep-sea vessels to operational systems in orbital spacecraft."
      - prvc 5y ago
        Ok, but's what's the value proposition for a purchaser, compared to cheaper alternatives?
        numpad0 5y ago
        Does it look like there are plenty alternatives?
dmitrygr 5y ago
> ARM SoCs from the early 2000s typically has an LCD controller that is capable of driving STN LCDs. However many of these SoCs are also being deprecated or obsolete. STM32F4 and STM32F7 series have plenty of cheap chips that support driving STN displays
- crest 5y ago
  Good look finding any original STM32 parts at the moment.
  - dmitrygr 5y ago
    Oh, did I miss RP2040 being ordereable in 100ku quantities? “Sometimes available” beats “toy” anytime
    - whiskers 5y ago
      Are you sure it isn’t available in those quantities? I think it should be.
      - ebenupton 5y ago
        It is. Both from (https://direct.raspberrypi.com https://direct.raspberrypi.com), and from various disties. Just shy of 300ku on hand at Farnell today (https://uk.farnell.com/search?st=rp2040 https://uk.farnell.com/search?st=rp2040).
    - lproven 5y ago
      In the thousands, yes. Reels of 3400 units are available. https://www.theregister.com/2022/01/17/raspberries_pi_direct_launch/ https://www.theregister.com/2022/01/17/raspberries_pi_direct... Hundreds of thousands, not yet.
crest 5y ago
The code could be improved by using DMA channel chaining instead of an interrupt to reload the two DMA channels.
- blacklion 5y ago
  From source: === Note that it is actually possible to eliminate this interrupt as well. The PIO and DMA could push pixels out automatically without any CPU intervention. However, I am not doing it here, because precise Vsync interrupts are quite useful. I could switch framebuffers here without any tearing effects. This is also critical to implement FRC for greyscales. ===
ultrarunner 5y ago
This is really great. I'm struggling to find SAM D5x chips and considering swapping in RP2040s instead. Seeing the flexibility in the PIO here makes that pretty tempting. What are people using for cheap ($5-$10/ea) displays now?
- fest 5y ago
  I use either monochrome SSD1306 based OLEDs for devices where display is more of a convenience than requirement. For nicer things, 2-3" IPS displays retail around this price, e.g. https://www.waveshare.com/2inch-lcd-module.htm https://www.waveshare.com/2inch-lcd-module.htm

36 points by _Microft 5y ago

1MachineElf 5y ago

I appreciate the depth of this guide. The display is gorgeous. Why aren't these more common?

mastax 5y ago
Expensive (this one is $700+), monochrome, fragile, dim, burn-in, high-voltage.
- prvc 5y ago
  Why so costly?
  - flaviut 5y ago
    Pretty much answered by the original question: > Why aren't these more common? There's no economies of scale. Looking at the ad for these in https://www.lumineq.com/technology https://www.lumineq.com/technology: "TFEL technology has proven its excellence in applications ranging from monitor and control instruments in deep-sea vessels to operational systems in orbital spacecraft."
    - prvc 5y ago
      Ok, but's what's the value proposition for a purchaser, compared to cheaper alternatives?
      - numpad0 5y ago
        Does it look like there are plenty alternatives?

dmitrygr 5y ago

> ARM SoCs from the early 2000s typically has an LCD controller that is capable of driving STN LCDs. However many of these SoCs are also being deprecated or obsolete. STM32F4 and STM32F7 series have plenty of cheap chips that support driving STN displays

crest 5y ago
Good look finding any original STM32 parts at the moment.
- dmitrygr 5y ago
  Oh, did I miss RP2040 being ordereable in 100ku quantities? “Sometimes available” beats “toy” anytime
  - whiskers 5y ago
    Are you sure it isn’t available in those quantities? I think it should be.
    - ebenupton 5y ago
      It is. Both from (https://direct.raspberrypi.com https://direct.raspberrypi.com), and from various disties. Just shy of 300ku on hand at Farnell today (https://uk.farnell.com/search?st=rp2040 https://uk.farnell.com/search?st=rp2040).
  - lproven 5y ago
    In the thousands, yes. Reels of 3400 units are available. https://www.theregister.com/2022/01/17/raspberries_pi_direct_launch/ https://www.theregister.com/2022/01/17/raspberries_pi_direct... Hundreds of thousands, not yet.

crest 5y ago

The code could be improved by using DMA channel chaining instead of an interrupt to reload the two DMA channels.

blacklion 5y ago
From source: === Note that it is actually possible to eliminate this interrupt as well. The PIO and DMA could push pixels out automatically without any CPU intervention. However, I am not doing it here, because precise Vsync interrupts are quite useful. I could switch framebuffers here without any tearing effects. This is also critical to implement FRC for greyscales. ===

ultrarunner 5y ago

This is really great. I'm struggling to find SAM D5x chips and considering swapping in RP2040s instead. Seeing the flexibility in the PIO here makes that pretty tempting. What are people using for cheap ($5-$10/ea) displays now?

fest 5y ago
I use either monochrome SSD1306 based OLEDs for devices where display is more of a convenience than requirement. For nicer things, 2-3" IPS displays retail around this price, e.g. https://www.waveshare.com/2inch-lcd-module.htm https://www.waveshare.com/2inch-lcd-module.htm