Ewa Wojno-Tomaszewska

Driving the segment LCD with MC9S08GT16

Discussion created by Ewa Wojno-Tomaszewska on Jul 3, 2008
Latest reply on Jul 11, 2008 by Ewa Wojno-Tomaszewska

I've read about possibility of driving segment LCD display using any MCU with Analog-to-Digital Converter. It is simple and the only trick is to generate proper voltage sequence on ADC pins used as “COM” pins.

To generate Vdd/2 necessary for the backplane a voltage divider is created using two equal sized pull-up and pull-down  resistors on ADC pin. Whenever ADC(=COM) output pin on the microcontroller is set to analog in, this voltage divider provide necessery VDD/2 voltage to the LCD. Whenever the COM output pin is set to digital output 1 or 0 will be sent to LCD. The role of segment pins is performed by digital output pins.

I managed to display all icons on the LCD, but I have a problem with displaying single icons as the icons that should be dark is still visible, only less clearly. It is particularly evident when the small  icon is to be displayed  and the neighbouring big icon should be invisible.

I can see that connecting LCD display causes noise on the COM signals, looked as interference from other COMs and digital segments ( when I disconnect the display signals are free of noises).

Did anyone try to use segment LCD display with common MCU and know how to eliminate that problem?