Driving TFEL LCD Panels with RP2040: Offloading the CPU Step by Step | Hacker News Reader

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

zephray.me

36 points_Microft16 comments

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I appreciate the depth of this guide.

The display is gorgeous. Why aren't these more common?

Expensive (this one is $700+), monochrome, fragile, dim, burn-in, high-voltage.

Why so costly?

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: "TFEL technology has proven its excellence in applications ranging from monitor and control instruments in deep-sea vessels to operational systems in orbital spacecraft."

Ok, but's what's the value proposition for a purchaser, compared to cheaper alternatives?

Does it look like there are plenty alternatives?

> 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

Good look finding any original STM32 parts at the moment.

Oh, did I miss RP2040 being ordereable in 100ku quantities?

“Sometimes available” beats “toy” anytime

Are you sure it isn’t available in those quantities? I think it should be.

It is. Both from (https://direct.raspberrypi.com), and from various disties. Just shy of 300ku on hand at Farnell today (https://uk.farnell.com/search?st=rp2040).

In the thousands, yes. Reels of 3400 units are available.

https://www.theregister.com/2022/01/17/raspberries_pi_direct...

Hundreds of thousands, not yet.

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?

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

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

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. ===

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