how to control the contrast of GLCD

[longpole001]

thanks hendric the voltage is about -6.0 to -7.5v on the wiper relative to ground for visual of the chrs ,

is there a way to just switch on/ off a mosfet which is connected from the GLCD negative output ( Vo) to the VLCD pin and adjust the voltage applied depending on the time the Mosfet is on using PWM ? ????

[Aussie Barry]

Hi Sheldon,

You obviously can't achieve a negative voltage directly from the PIC so you will need some external circuitry (including a negative supply greater than -7.5V).
It should be possible to drive an inverting op-amp, with a gain of say 2, via Henrik's filtered PWM signal such a positive input will result in a negative voltage at the GLCD contrast pin.

Just a thought...

Cheers
Barry
VK2XBP

[richard]

pwm through an opto coupler would be easy, driving things on the neg bus from the positive side are awkward opto's make life easy