7 Segment LCDs

Not to be confused with the alphanumeric type that uses 8 bit data Lines.

Ive forgotten how 7 Segment LCDs work, I know that they need a Frequency of 30hz or greater to be connected to the backplane (or common as some call it), but as for the actual segment activation, Do They need to have a clock, or Can they be High Or low (such as in turning on or off 7 segment LED displays? ).

Check out the PIC 16F917 datasheet, there is a section on driving LCD glass.

segment activation: the segments need to be driven with the reverse phase of the backplane.

Direct DC will very quickly destroy and LCD display.

blueroomelectronics said:

Check out the PIC 16F917 datasheet, there is a section on driving LCD glass.

Click to expand...

Ahh, I see. Lit segments need to be Out Of Phase with the clock, while unlit segments need to be in phase. Hrm, Ultimately, I want to be able to use them with the PIC18F Series, I figure use one of the PWM outputs as the backplane and use XOR gates to control which segments are lit up, that way I can use code that was orignally for a LED 7 segment display and adapt it for a LCD display

Ah, I remember this stuff now, this page brings back memories
**broken link removed**

EDIT-Actually, thats two many IC's that Id have to use. Probably easier to keep it in BCD and use a 74HC454

There are 18F PIC with LCD controllers..

blueroomelectronics said:

There are 18F PIC with LCD controllers..

Click to expand...

Yea, 88 Pins . Kinda hard to breadboard with/program/design around.

64pin TQFP too, not too bad to solder. Easy with a Schmartboard adapter.

National Semiconductor makes a couple chips designed to drive this type of LCD. The part numbers are MM5452 and MM5453. They have 32 (MM5452) or 33 (MM5453) outputs and use a synchronous serial interface for data transfer.
**broken link removed**

Jeff

jbeng said:

National Semiconductor makes a couple chips designed to drive this type of LCD. The part numbers are MM5452 and MM5453. They have 32 (MM5452) or 33 (MM5453) outputs and use a synchronous serial interface for data transfer.
**broken link removed**

Jeff

Click to expand...

hi,
I have used the MM5453 many times, its an excellent device for driving LCD's.
On board R/C back plane osc.
The size of MM enables it to be mounted under the LCD, between the LCD sockets.

If you use transmission type LCD's a strip of reflecting foil, stuck to the MM and a couple of wire ended 5V lamps gives a good result.

Also the 4 connecting wires [twisted] can be upto 10ft in length.

If you need to drive a 5 digit LCD or more, use HEF4035 S/R's and connect the T/C on the 4035 to the back plane.