how to control the contrast of GLCD

[longpole001]

the glcd generates the negative supply so using an opto transistor connected to the negative Vo output of the glcd to the glcd VLCD input ( contrast control ) is possible , not sure how linear an opto fet would be to adjust the voltage for the contrast though ,
I had looked at a digital pot , but seems that the voltage cant be negative on the resistor divider network , in respect to the chips supply vdd and grd rails.

[mark_s]

Hello,

Maybe something like this using a pnp in a open collector configuration. Much like we control a 12v relay with a NPN and a 5v mcu. Set the PWM to 50% duty and adjust the contrast pot to good level. Now you should have a +/- contrast changing the duty. Basic idea only. Might want to add a resistor and cap to the pwm line to smooth it out.