Driving the segment LCD with MC9S08GT16

marigold80 — Thu, 03 Jul 2008 13:48:04 GMT

Hello,
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?

Regards,

Marigold

Re: Driving the segment LCD with MC9S08GT16

marigold80 — Fri, 11 Jul 2008 15:02:54 GMT

Hello,
if anyone is interested in solution of described problem: everything works just fine, the problem was caused by damaged heat seal connection of displays (floating COM signal).

Regards,
Marigold

topic Re: Driving the segment LCD with MC9S08GT16 in 8-bit Microcontrollers

Driving the segment LCD with MC9S08GT16

Re: Driving the segment LCD with MC9S08GT16