Salvaged LCD from pen-clock

Hi !

I'm new to this forum. I hope you will be able to help me :slight_smile:

I'm trying to use a small LCD from a pen clock (around 0.70€) :

My goal : drive it with an Arduino (or another AVR) to use at least 2 digits.

I opened it and checked the PCB :

There is 13 connectors on the LCD.
The battery is a 1.5V button battery.

I soldered a wire on each LCD connector :

I tried to look at the signals on each wire (I do not have an expensive oscilloscope (it's a DSO138).
It seems that the LCD is multiplexed, with two commons (one on the left, one on the right).

Common signal :

Segment signal :

It seems quite near some explanations I found here :

But my problem is that the signals are between Vss and Vcc, with Vss = -1V and Vcc = 1.5V.
How can a produce such a signal with the output of an Arduino ?
On the PDF file, they are using Vss = GND, which is not my case.

Do you see any other problem that I can encounter ?

Thank you for your help,


You have probably solved your problem by now, but here is the solution:

You can create an AC with three levels of positive DC voltages to drive these LCDs.

V1 = 0V DC
V2 = 1.5V DC
V3 = 3V DC

You can alternate among these voltage levels.

Please read “Zilog’s Direct Drive of LCD Displays” pgs. 2-3.

Or you can use an H-Bridge to create the AC.

Oh, by the way, forgot to say.. You should have an AC around 25-30HZ to drive these LCDs. Below frequencies will produce visible flickering. And above frequencies will increase power consumption and shorten the life of the LCD.