Pictured in this product...



...is a PC board that has an Intel N87C51FA24 in a PLCC-44 package. The PLCC part is on a PLCC socket and then on either side of the PLCC socket there is a single in-line strip socket of 12 pins. An LCD bare glass module eqipped with dual in-line leads is able to plug directly into the two strip sockets. The various decimal point and the segment select lines connect to the port pins of the processor directly. There is also a back plane signal which also connects directly to the LCD module from a port bit. This is a "feasible solution" in that it does work to make about as cheap of display as you could imagine.

However the software to drive the display does require care to get the back plane driver at extremely close to 50% duty cycle as possible. If not you can get an average DC bias built up on the crystals in the LCD fluid which is not a good thing.

That said, the types of displays that are suitable for this type of minimalistic display tend to be some what limiting. The above product had a standard off-the-shelf 3 digits of seven segments plus decimal points. It sucked up 24 processor I/O pins and was basically good at just displaying numbers.

There is an unavoidable thing that comes up however. The customer will look at the display on his cell phone or the graphics on his notebook PC and want his product to display more than 3 seven segments can handle or he will want the displays to look better or more realistic. This is the reason the product I pictured above is slated for re-design to use a different type of display. We will likely be using something like the 106x56 COG (chip on glass) module shown here:



The display area on that is about 0.7 x 1.35 inches. The module is supported with a serial interface which is relatively easy to bit bang. I think the extra utility of such a display far outweighs its cost difference over the bare glass module and the hardware resources it takes to support it (i.e. many port pins or separate external driver chips). If you had considered using a display like this but were held back by the software it would take to support it you should go to my 8052.COM Projects / Articles Page and look at my article on using bit-mapped fonts on graphics LCD modules. There is some nice free software there you can download and use.

Have fun
Michael Karas