Driving LCD contrast and Brightness

Started by mrrmckenzie June 8, 2005
Can anyone supply circuits for driving contrast and brightness on an
LCD connected to a BX35. I have browsed the Group messages and cannot
see anything. Essentially I wish to build something similar to the LCDX
but without all the pin consumption. Basically I would like to use the
same technique LCDX uses to drive its display.

Thanks
Rod


I have been thinking of the same issue. It is clearly possible since
the LCD's cold by BasicX do it.

But, assuming that you are using a raw parallel-type of LCD it is not
so easy.

Running the backlight of my LCD uses a series resistor of about 33-68
ohms go give a "medium" level of back light. The current draw exceeds
what the BX-24 can supply on its own.

I had considered using PWM to a transistor (also with a series
resistor to limit the maximum brightness) to power the backlight. I
also came to the realization that I do not need to use the regulated
power for the backlight. Of course the backlight intensity will vary
with the power supply voltage, but set the series resistor for the
worst case scenario, and proceed from there. As for the contrast, I am not sure that PWM driving of the LCD will
work. Maybe it would be necessary to have a "digital potentiometer"
being used as a voltage divider. Those devices are not good for much
current, but I do not think the LCD contrast pin draws much....

I will be interested to see what other REAL solutions people offer!

-Tony

--- In basicx@basi..., "mrrmckenzie" <mrrmckenzie@y...> wrote:
> Can anyone supply circuits for driving contrast and brightness on an
> LCD connected to a BX35. I have browsed the Group messages and
cannot
> see anything. Essentially I wish to build something similar to the
LCDX
> but without all the pin consumption. Basically I would like to use
the
> same technique LCDX uses to drive its display.
>
> Thanks
> Rod