used grayscale lcd panel for sale

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The first thing you will need to consider is your intended purposes. Some screens are intended for medical use while other screens are intended for use with a personal computer. Deciding if you want an LCD or CRT screen will be another factor. LCD screens create sharper images, but you can find used CRT screens at a lesser price. You will also want to consider what kind of computer you intend to hook it up to if you are buying for a personal computer. Also, check to see if it is refurbished, new, or used. Refurbished means that the monitor has been checked and anything that is broken has been fixed. If a monitor is labeled as "used," then it hasn"t been tested, so you"re taking more of a chance on how well it will work.What is the difference between LCD and CRT monitors?

LCD stands for "Liquid Crystal Display." It"s often used in laptops and flat-panel computer screens, and it produces clearer images than CRT screens. In an LCD screen, liquid crystals rotate polarized light to create the image. CRT stands for "Cathode Ray Tube." It was often used in computer monitors and televisions screens until the LCD and plasma screens replaced them. This type of screen creates images by sending electrons from the back of the tube to the phosphors at the front of the tube.

This development kit is for a backlit, low-power, graphic, high-density, 4-shade grayscale LCD. This kit is a great jumping-off point for developing your project and it includes everything needed to quickly develop a working demo.

Meet Barco Coronis Uniti MDMC-12133 12MP Color PACS and Mammography Display. The only display explicitly designed for both PACS and breast imaging. Unique in its representation of calibrated color and grayscales. Remarkable in its 2D and 3D capabilities. Capable of both static and dynamic imaging. Together, these features will forever change the way you work.

ER-OLED015-3W is the graphic OLED display panel made of 128x128 individual white OLED pixels,16-level grayscale diagonal is only 1.5 inch.The controller ic SSD1327, communicates via I2C,4-Wire SPI Serial or 8080/6800 8-bit Parallel,, interface,thanks to controller"s built-in voltage generation,only a single 3.3V power supply is needed. Because the display makes its own light, no backlight is required. This reduces the power required to run the OLED and is why the display has such high contrast,extremely wide viewing angle and extremely operating temperature.The fpc is the soldering type,no need connector.Just solder the FPC on your PCB directly.

It"s easily controlled by MCU such as 8051,PIC,AVR,ARDUINO,ARM and Raspberry Pi.It can be used in any embedded systems,industrial device,security,medical and hand-held device.

Barco"s MFGD 3420 is a 3 MegaPixel stand-alone display version of Barco"s successful Coronis® flat panel display system. Its accurate signal conversion and high brightness make it a perfect solution to upgrade existing CRT-based systems with state-of-the-art technology. The bright 20.8” display can be used in dark reading rooms as well as ambient light environments. It comes standard with a solid tilt and swivel base, allowing users to adjust the panel"s position to their preferred viewing angle or easily switch between landscape and portrait mode. The display is also equipped with a protective glass cover for perfect image rendering and easy cleaning.

If you"ve been following this blog lately, you"ve probably noticed there is a series of blog posts called LetsDriveLCD where I buy random LCDs and drive them to display something. Most of them are passive dot-matrix LCDs: the reflective monochrome screens with a green-ish tint. Many portable devices made late last century and early 2000s featured this type of display. While they are almost extinct on modern consumer electronic devices, they could still be easily found on various embedded devices.

Today I am going to do something similar, driving a 320 by 100 pixel reflective FSTN LCD screen, with de-facto industrial standard STN LCD pixel interface. First try display the following image:

It’s still outputting to a 1-bit screen, but now I could see more details from the image compared to the direct clamping. There are many ways of doing the dithering, the one used here specifically is based on error diffusion. Let’s take a closer look.

Say I have an input image, that’s 8-bit grayscale, and output is 1-bit. Or in otherways, if to represent the output in the input range, the output could be either 0 or 255. Anything in the middle is unavailable. To choose the output value based on input, a quantizer is introduced here: if the input is larger than a half, or 127, then it outputs 255, otherwise 0. This is what I have been doing before, clamping the image to black or white directly.

But something is off, I remember these screens could do many levels of grayscale, like on these devices they could all display different shades of gray or green. However, almost all of the screens I got were 1-bit mono. Initially I thought this is probably because the screen I got was for industry control or similar stuff so they don’t need that. Only the screen for consumer electronics would have greyscale support. Which turned out to be false. I took apart some devices that have 16 levels of grayscale and found out that the screens themselves are 1-bit screens. What’s the trick there? Let’s take a deep dive into this.

So now I am now given a screen that could either display black and white, and I would like to display different shades of gray on the screen. How to do that? Well if I use another analogy to that: I have a digital output pin which could be either high or low, and there is an LED connected to it. And instead of just lighting up or shutting off, I want to have a different brightness. Does this sound familiar? There is a commonly used technique called PWM for doing this. Basically define a period, and for some time in this period the output is high, and the rest is low. Then the whole period gets repeated over and over. If this is fast enough that eyes couldn’t detect, one would think it’s some brightness in the middle, instead of it being switched on and off rapidly.

Can I do the same on these monochrome LCDs? Yes and no. There are some LCDs that have PWM built into the driver chip, so they natively take multiple bits per pixel as input, and would modulate the greyscale during the screen refreshing process. One example is that GameBoy’s screen takes 2 bit per pixel input natively and produces 4 level grayscale.

Well then if the screen driver chip doesn’t have PWM built-in, can I still use PWM on a maybe higher level? You see, LCD, to keep display, needs to be constantly refreshed. So if I look at a single pixel, it’s being driven at a constant interval, and I have control over the level, being either high or low. In this sense, I could simply put a PWM waveform there.

For example, if I want 16 level grayscale, then I can have a PWM period of 15, then based on the output level, the duty cycle would be 0 to 15 cycles. Sounds great. Does it work? Let’s see.

To code it, there are 1 bit-per-pixel frame buffers that would be sent to the screen. And there are 8 bit-per-pixel frame buffers that would hold the grayscale image to be displayed. Now I just need to write a function that does the software PWM on these buffers.

While it probably looks decent in the picture, actually the image is quite flickery and the reason should be obvious. The minimum unit of output is a frame, or at 120Hz refresh rate, about 8.3ms. If the PWM period is 15 cycles, that’s 15 frames, or 124.5 ms total. This translates to a PWM frequency of only 8 Hz, surely it would flicker pretty bad. I could reduce the PWM period down to say 3, so the PWM frequency is up to 40Hz for a sort of steady image. But obviously the grayscale level is then reduced to 4 levels.

I get grayscale and it’s all good now right? Something is still off. I know these devices could get 16 level or even high levels of grayscale out of these 1-bit screens. So there must be a better way to do that. After reading some papers, I found out typically this is done by using optimized sequences. For example when outputting the 50% gray, if the PWM period is set to like 16, it would be 8 cycles high and 8 cycles low, then repeat. But to reduce flicker, it could be just 1 cycle high and 1 cycle low, then repeat, still maintaining the same 50% duty cycle.

Some may recognize this and say, isn’t this just mimicking PDM? Yes it is but hold on to it for now. The code for using such sequences is also straightforward. Again I keep a period counter, from 0 to 30. Instead of directly comparing the pixel value with counter value to produce a PWM waveform, both are used as index into the sequence look up table to derive the value to use.

Now running the code, I am almost getting 32 grayscale levels. Except some levels are still flicky. This is totally understandable, for these levels, the optimization doesn’t improve much. For example in the extreme case of the lightest level that’s not pure white, that just 1 pulse in 31 cycles. It doesn’t matter where you put that pulse.

Then what’s next? What to do with these flickery levels? Well there are 2 possible ways to fix that. One is to simply not use these duty cycles. In the sequences I crafted, the duty cycle linearly corresponds to the input gray level. This is not really required and this is also not what’s typically done. There are many duty cycles that have a shorter period but are not used in this 31 frame sequence. For example, like 5/9, 3/5, 3/4, 7/8, etc. I could use these sequences to replace ones that’s too flickery. I also don’t have to start with 1 pulse, I could start with a, say 1/8 duty cycle at the lightest gray level.

This method of using a sequence table along with other optimizations to generate grayscale is typically called frame rate control, or FRC for short, while it doesn’t really control the frame rate at all. As a result, I have implemented what’s typically done on a grayscale LCD controller from last century. I have also got 32 levels of grayscale out of this 1-bit LCD. The difference is that typically these are implemented on hardware, but I am here emulating these with software. But as you could see from the video progress bar, I am not finished yet.

Cool, now the issue left is just the gamma correction, or grayscale calibration. As you could see, the screen response is quite non-linear, many levels near white and black are not usable. To get more usable levels, I am bumping up the total grayscale levels to 64.

How am I going to do that? I cannot change the relation between output value and brightness level, but I can change how input is mapped to output. The input image is 256 shades, but output is 64 shades. I could just craft a table to map 256 shades into 64 and compensate for the non-linearity. Color LUT calibration on a monochrome LCD, did I go a bit too far?

To be honest, I didn’t come to this stage by accident, I have worked with delta-sigma modulators and noise shapers in audio applications before so I know these, and I have been wondering about if they could be applied to driving these LCDs for a long time. I looked through many different LCD controller manuals, searched many relevant papers, but it seems like no one is doing that. Finally I decided to just try myself and see if it would ever work. Now we can clearly see it works. But is it worth it?

You see, in order to implement this feed-back loop, I had to create a state buffer for it to remember the accumulated error for each pixel. For the controller, the processing for each pixel is now a read-modify-write process to a large buffer compared to a table lookup. This additional complexity could mean a lot. In this proof-of-experiment I am using the microcontroller to emulate an LCD controller, but in real life applications, that would be an ASIC. If the LCD controller is originally like these self-refresh controllers, then it would need to double the size of internal RAM. But if the LCD controller is like those without memory at all, like a controller taking VGA input and outputs to the screen, this means it now needs to implement an external memory controller and a whole set of pipelines just for this.

Now let’s look at dynamic response, or basically, playing back a video. The video I am using is the Sintel movie by Blender foundation, licensed under creative commons attribution 3.0. Just for the sake of fun, let’s first see the result with direct clamping, 1-bit spatial dithering, and the 4 level PWM grayscale.

In conclusion, in this blog I explored and implemented various different methods of producing grayscale images on these passive matrix monochrome LCDs. In addition to use industrial standard methods, I have also tried using noise shaping technology commonly used in other applications here and got some fairly good results as well. That’s it for today, thanks for reading.