How to Run a Statically Driven LCD display 1

[Tsiolkovsky]

Hi all,

I have attached a 2 page spec sheet on a an LCD display component that I am trying to get to work. I am conforming to its 3V operating voltage by supplying it 3V to the pins. The display only flickers for a second and sometimes not at all. The component itself works and have cross checked it with others. My question is, how are LCD display screens wired up to work?

I notice that on the spec sheet there is a line on page 2 that mentions "driving method: static". A colleague mentions this as the culprit. The LCD needs to be driven by a driver. Can someone tell me what components I need to make this thing work?

Regards,

 

[zappedagain]

Start with the LCD manufacturer (Clover?); they probably has a demo board available to drive it. That should have documentation on the driver that they use. If not, start with another manufacturer that provides better design support unless you are stuck using this one (and a very experienced EE).

For example, I recently used a New Haven Display NHD-2.4-240320SF-CTXL#-FTN1 and they also sell the NHDev evaluation board to drive it and recommend an ILI9341 driver.

A lot of microcontrollers have built in LCD drivers (TI, Atmel, etc.) so you might look there too.

Z

 

[LiteYear]

Not much to go on there is there? I assume you've searched for a manual or a datasheet. I'm not familiar with this type of display, but based on that drawing, I would guess that the method of operation is as follows:

1. Apply a current-limited 3Vdc across pins 2 and 1, with the positive on the 2.
2. Slowly increase the current limit until the '-' sign appears. If nothing happens up to about 20mA, then stop, something isn't right.
3. If the '-' sign does appear, briefly increase current up to about 25mA to see if there's current limitation built in.
4. Do the same for pins 3 and 1, which should cause the first '1' to appear.

That should give you enough information to get the rest of it working.

The "static" bit most likely just means that it can be DC driven. Some LCDs require a high frequency supply to keep the cells operating. I don't think a 240x320 TFT driver (the ILI9341) is the way to go for a few 7-segment displays.

 

[jimkirk]

These displays require an AC waveform to drive them. Typically the common line is driven with a square wave (tens to hundreds of hertz), Vcc and ground. An OFF segment is driven with the same phase as the common, so the net voltage across it is zero. An ON segment is driven out of phase, so there is a +/- Vcc square wave across that segment.

Here's an example from Atmel...

http://www.atmel.com/Images/doc2569.pdf

As I recall, a sustained DC bias will eventually damage the display.

 

[Tsiolkovsky]

Thanks Guys. LiteYear, Ill give your suggestion a try.

Jim, thanks for the link. Could you possibly provide me a "step by step" guide in order to make it work? I really don't know where to start.

 

[LiteYear]

Oh, I'm quite mistaken! Go with jimkirk's answer - the reference specifically defines "static" which is quite different to my interpretation.

 

[Comcokid]

What you need to find is a static-mode LCD driver IC. Static mode uses one-drive-pin-per-LCD-segment verses dynamic or multiplex drive that controls several segements with each drive pin. Static mode gives better viewing angle, contrast, and is used for LCDs in a wider temperature range environment.

Each segment is driven with a square-wave signal as jimkirk described, with the backplane as the common of the square-wave signal. A segment (in positive-mode LCD type) that is in-phase with the backplane does not show, while a segment driven 180 degrees out of phase will show.

Your LCD seems to have several backplanes in the description. This may be so it can be more usuable for some non typical applications (like a processor with several ports emulating a LCD driver, and one pin of each port emulating the backplane??). Most drivers will have plenty of output drive pins but one backplane pin. In this case, just hook all the LCD backplane pins together to the one driver backplane pin.

 

[Tsiolkovsky]

Thanks will do.

As a matter of interest is it possible to just use a shift register to drive the LCD screen without a drive?

I refer to the link below:

http://blog.hovertop.com/2012/07/driving-a-16x2-lcd-with-shift-register/

 

[Tsiolkovsky]

Although in that link its a character lcd and not a CMOS segment lcd like the one om trying to get to work

 

[Tsiolkovsky]

Sorry this thread doesnt allow editing of posts. I meant to say is it possible to run the LCD with just an IC/PIC and a shift register? Can the PIC in of itself be the driver? All I need to do is programme the PIC to output two square waves 180 deg outta phase from each other and hook it up to the pins

 

[Comcokid]

A microcontroller with a lot of port pins can drive the controller. Since you only need to drive the segments with a square-wave at, say, 60 to 120 Hz, you can write you code to have a timer interrupt at this rate, and when you service and reset the timer complement the value on the ports. Assign one pin as the backplane.

There are also microcontrollers with built-in LCD drive capability where the timers/ports are setup to make this much simpler.

Another old hardware way used shift registers and XOR gates. Or was it NOR gates? can't recall exactly.