Graphical LCDs: alternatives and drivers

[KrisBlueNZ]

Hi all,

I've taken on a design project that will need a monochrome graphical LCD, and I've never worked with LCDs before, so I would appreciate any advice!

The application is a small display unit to be permanently mounted in a special-purpose slow-moving vehicle, to display information to the driver/operator.

We're currently looking at the Crystalfontz CFAG19264A-YYH-TN module (https://www.crystalfontz.com/product/CFAG19264AYYHTN) with 192x64 dots and a viewing area of 102 × 39 mm. Dot pitch is 0.5 mm (50.8 dpi).

It is a module with a parallel MCU interface, with an STN positive display with a yellow-green LED backlight, transreflective (I don't really know what transreflective and STN positive mean), 6 o'clock viewing direction, and an internal negative voltage generator.

It requires a 5V logic supply, an "LCD operating voltage" of about 8V, and a backlight supply of 540 mA at around 4.2V (4.4V maximum). These shouldn't be a problem, although the 8V supply is a bit of a nuisance. There's no specification on how much current it needs.

The module includes a controller which is apparently compatible with the Samsung KS0107 (https://www.crystalfontz.com/controllers/DS_S6B0107_V00.pdf) or KS0108 (https://www.crystalfontz.com/controllers/DS_S6B0108_V00.pdf) operating at 1:64 multiplex ratio, and is available with a demonstration board (https://www.crystalfontz.com/product/CFA10006.html) that has an Atmel ATmega2561 (AVR architecture) on it.


I'm interested in any limitations this display may have, and any suggestions for alternatives. The contrast ratio is typically 3, and the viewing angle (at a contrast ratio of at least 2) is from 20° to 40° vertically (view direction is 6 o'clock) and -30° to +30° horizontally, which seems reasonable. The response time (ON and OFF) is typically 200 ms, maximum 300 ms. That's pretty slow but I don't think it will be a problem since the display will be static most of the time.

I'm also aware that some microcontrollers can drive LCDs directly, but I'm not sure whether they could drive STN displays with lots of pixels. If we could avoid the driver IC(s) we would save some cost. I have experience with AVR, PIC and MSP430, and would be willing to consider other options too.

Any other information, warnings, guidance, etc would be very helpful. Thanks

 

[Arouse1973]

HI Kris

Sounds an interesting project. Trans-reflective LCDs use daylight as the backlight so you can see the graphics. The backlight then is used when the light level is insufficient. You could for energy reasons have a light sensor which activates the backlight in certain light levels. This is what I did for one of our products

Although some people feel the need to have the backlight on all the time especially if the back light is a nice blue colour

Don't know much about STN displays but I think they are the sort on some of the cheap phones and have limited quality.

The only issue we have had with the LCDs we use is temperature, they don't like going too hot or too cold. Although the data sheet might say works to -30 degrees and +60 degrees, it might well do but you won't see anything on the screen

Good luck, keep us posted
Adam

 

[BobK]

I am not sure if this applies to the graphics LCD that you are using, but the LCD voltage on text LCDs is normally supplied through a 10K pot which is the contrast control, so very little current, and it might need to be adjustable.

Edit: Oh, and read the datasheet carefully about that. It is usually specified as a negative voltage WRT Vdd, so that is where your negative voltage generator comes in. The pot should go between Vdd and the negative voltage (which, if I am right should be -3V or more.)

Bob

 

[KrisBlueNZ]

Sounds an interesting project.

No, it really isn't

Trans-reflective LCDs use daylight as the backlight so you can see the graphics. The backlight then is used when the light level is insufficient. You could for energy reasons have a light sensor which activates the backlight in certain light levels. This is what I did for one of our products

OK. I don't think that will be an issue - the backlight will be ON constantly.

Although some people feel the need to have the backlight on all the time especially if the back light is a nice blue colour

Yeah, that would be nice. Or white. Yellow backlight looks very 90s.

Don't know much about STN displays but I think they are the sort on some of the cheap phones and have limited quality.

Right... What would you suggest instead? TFT?

Are TFT displays available in monochrome? Colour is really unnecessary.

Are they available with low pixel density? 50 dpi would be fine, and much more would just make it difficult to drive.

The only issue we have had with the LCDs we use is temperature, they don't like going too hot or too cold. Although the data sheet might say works to -30 degrees and +60 degrees, it might well do but you won't see anything on the screen

OK, thanks for the warning. I don't think this unit would be used beyond 5~25 °C.

Good luck, keep us posted

Thanks I will.

I am not sure if this applies to the graphics LCD that you are using, but the LCD voltage on text LCDs is normally supplied through a 10K pot which is the contrast control, so very little current, and it might need to be adjustable.
Edit: Oh, and read the datasheet carefully about that. It is usually specified as a negative voltage WRT Vdd, so that is where your negative voltage generator comes in. The pot should go between Vdd and the negative voltage (which, if I am right should be -3V or more.)

OK. The signal is called V₀ and is specified as 7.2~9.2V negative relative to VDD, as you said. That display module includes a negative voltage generator, and the demonstration board has an op-amp that's controlled from a PWM signal, to set the voltage on that pin. Thanks for the info!

 

[Arouse1973]

Yeah monochrome TFT could be the way to go. Wide viewing angle and reads in sunlight. Varitronix are the people we have used in the passed, also Pacer. Check them out.

http://www.pacer.co.uk/?gclid=COf085n09cECFQjHtAodIFoARw
http://www.varitronix.com/product/index.php?option=com_content&view=article&id=42&Itemid=67

Adam