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I want to manage an LCD HD44780 display connected trought my Raspberry Pi B+.

The backlight pin (on Hd44780 display) need a resistor and I have 2 different display version, so the resistor value are little different.

To avoid changing resistor value every time I change display, I heard that is possible to control GPIO pin output voltage. So I'll adjust the voltage output according to the display connected.

Is there a python script or something else to do that? Maybe like this:

pin.setVoltage(1.5)

EDIT:

Display datasheet

As mentioned in answers and comments, the problem is to control the LCD backlight using GPIO pin, without resistor, maybe doing it with PWM pin.

Thanks!

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  • Tell us more about the specs of the 2 different resistors - and if possible, the input spec for the backlight pin. There might be a common resistor value that would work for both. I'm not aware of the ability to change the output voltage of a GPIO pin - you can vary the power of the pin through PWM but not the specific voltage - that would require a DAC output pin.
    – Phil B.
    Sep 11, 2015 at 22:46
  • You can use PWM to vary the backlight intensity. I've used the technique on the backlight LEDs of a TFT display. That's probaly what @xPino saw. It is certainly worth trying
    – joan
    Sep 12, 2015 at 7:34
  • @joan any experience with python code to use PWD? thx
    – xdola
    Sep 13, 2015 at 13:32
  • @xPino All the Python modules will have a PWM function, the name and how it is used will depend on the module you want to use.
    – joan
    Sep 13, 2015 at 13:38

2 Answers 2

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In general, no - GPIOs don't have a variable voltage output. If they did, we'd call them a DAC.

As suggested by xPino, you might be able to use a PWM pin - but I suspect that the backlight pin on the LCD is going to have higher current requirements than can be provided by a GPIO (or PWM) pin on the Broadcom. You'll have to look at the LCD datasheet to find out.

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  • I've edited my question with datasheet: I can't find the infrmation about backlight. BTW thanks
    – xdola
    Sep 13, 2015 at 13:31
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As the PWM pin probably doesn't supply enough current for the display, you can connect the pin to a transistor or MOSFET which in turn switches the backlight on and off very quickly to compensate for the different resistances.

If manual control is fine, you can also connect a potentiometer to the backlight and control the brightness by adjusting it manually.

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