LCD drive signals

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Figure 7.

LCD Timing Diagram for a single segment

2.3.1

LCD mean voltage calculation

The LCD mean voltage must be very close to zero to guarantee long life to the LCD. The LCD mean

voltage for ON and OFF periods can be calculated as:

Vmean(ON) = 1/8 Vseg + 1/8 (-Vcom) + 3(Vseg - Vr/2) + 3(-Vr/2) ----(1)

Vmean(Off) = 3(Vseg/2) + 3(-Vr/2) -----(2)

Vmean(ON) and Vmean(Off) assume identical periods for each phase.

From eqn (1) & (2), to get Vmean(ON) and Vmean(Off) = zero

Vseg = Vcom = Vr = Vcc

Where:

Vcom = Max voltage on COM line

Vr/2 = Voltage in the middle of the resistor bridge applied on the COM line

Vseg = Max voltage on Segx line

Vcc =

Microcontroller power supply

Segx

Segx_1 (ON)

Segx_1(off)

Vsegx

Vsegx

Vcom1