Hi All. I have a few questions regarding 16x2 LCD displays:

My project currently has a display that I'd need to swap out. It is a 16 character 2-line display. The first picture shows a typical pin out for currently commonly available 16x2 LCD's. The second image shows my existing LCD and the pin-labels.

(1st question) I see replacement boards seem to all have the same pinouts. Mine has an extra pin someplace. On you pic, you can see it labeled as XR. Anyone know what this pin is for? The replacement LCD's don't seem to have this extra XR pin. Do you think I can just leave this wire not connected? Since it's there and wired into the circuit, I'm sure it's there for a reason. Incidentally -- ignore the 3 wires on the right. Those go to the IR detector/sensor which replacement LCD's don't have.

(2nd question) Can larger (such as 20x2 or 24x4) LCD's be installed? I see the pinouts are the same regardless of how many characters per line. Will the display just do less scrolling?

(3rd question) The 6th pin from the right. Anyone want to guess what that pin is for? I'm guessing the 3 pins on the far right in the block are for the IR. The second long block starting with VCC I presume is for the LCD connection. But then if you count the labels and the pins, there's an extra unmarked pin someplace. What's your best guess guys insofar as the pin labeling?

(4th and last question) I am interested in installing a VFD display in it's place. However those all seem to use a serial bus instead of the LCD interface. Does anyone know of an off the shelf interface or a solution to make this swap possible. I prefer the VFD due to looks and better readability.

 

The only time I've seen XR is on touch screen LCD displays, Should have XL, YT, and YB as well. X-Right, X-Left, Y-Top, Y-Bottom

I am guessing that may not be a HD44780 LCD controller board on the LCD, so a drop-in replacement may not work.

If it is the same interface, hooking up the lines except the X/Y outputs would work, as long as the power and backlight are wired correctly, you shouldn't damage anything. The worse would be the LCD displays funny characters or doesn't work at all.

As far as putting a 4 line LCD in place of a 2 line, the microcontroller/processor that is writing to the LCD needs to know a 4 line is connected, or it will just use the top two lines, or you may get other odd results depending on the uc's program assumptions.

VFD displays are controlled similar once the high voltage is taken care of, but a lot different. It is similar to the difference between using an LED and LCD display. It can be done if you can change the code on the controller, but otherwise, not really.

 

The only time I've seen XR is on touch screen LCD displays, Should have XL, YT, and YB as well. X-Right, X-Left, Y-Top, Y-Bottom

I am guessing that may not be a HD44780 LCD controller board on the LCD, so a drop-in replacement may not work.

If it is the same interface, hooking up the lines except the X/Y outputs would work, as long as the power and backlight are wired correctly, you shouldn't damage anything. The worse would be the LCD displays funny characters or doesn't work at all.

The original display is definitely NOT a touch screen. So the HD44780 LCD controller board you speak of is actually part of the LCD module, right? It seems like the HD44780 controller is all I really see available right now. When I compare the labeling of the pins on the current LCD module, everything seems to match up except the XR pin is missing on the new module and one pin seems not labeled on the old one which I presume is VDD. Do you think it would be safe to try connecting a new LCD module matching up all the existing connected wires that I could cross to the old one? That leaves the XR wires as the odd man out. The rest of the wires indicated by the datasheet as required by the new LCD's seem all accounted for so perhaps new LCD's don't need the XR wire? Also, I noticed that not all the data wires are used in the existing display. Does that sound right?

 

Yes, you can hook it up matching the existing wires and leaving out the ones unaccounted for.

You can write to an LCD in either nybble mode (4 bit) or byte mode (8 bit). They are sending everything in 4 bit mode, so it uses fewer controller I/O pins. Just wire it the same and it should be good.

Ignore XR, is there a wire to XR? Just curious, it shouldn't matter, as it is an output from the LCD, not an input to it, unless this XR is an entirely different one than I've seen.

 

Yes, you can see the solder pad where the wire is connected so there definitely is a wire there, although whether it's just there because the manufacturer didn't want to leave one wire unsoldered in the middle of the ribbon is unclear. The controller assembly looks rather fragile with all the miniature components plus it's two small boards stacked up tight so hard to see where it goes, and what other chips are on the assembly.