I've installed an I2C module on my 16x2 LCD so i don't have access to all those LCD pins to control the backlight LED.

BUT there is a 100 ohm smd resistor in series with anode of the backlight LED, i want to remove the resistor and use Arduino PWM to control the backlight or i can just replace that resistor with a 330 ohm or a 1K resistor.

Red box showing the resistor and blue box showing the Jumper.

Also I2C module itself have a jumper for LED backlight which also goes to that resistor...

Just wanted to ask here and make sure it is going to work before doing any modification to the LCD.

which way is better? is it going to work?

UPDATE: i used Arduino PWM and a 2n2222 transistor and was able to successfully control the backlight brightness via jumper pins of I2C module.

  • Possibly. Do you have a schematic of the I2C module?
    – Majenko
    Jul 9, 2019 at 21:07
  • @Majenko this is the datasheet i found Jul 9, 2019 at 21:11
  • not sure why i got a down vote... Jul 9, 2019 at 21:13
  • 1
    Probably because you were very vague.
    – Majenko
    Jul 9, 2019 at 21:13
  • @Majenko or maybe people really want to finish that down vote achievement ;) Jul 9, 2019 at 21:16

1 Answer 1


It's hard to tell from the limited information, but chances are the "backlight jumper" mentioned in passing in the datasheet can be simply removed. This will then give you two pins. One will connect to pin 3 of the IO expander, and the other will connect to the back light anode itself.

Which is which you will have to discover for yourself. One of them will have the 100Ω resistor in line with it as well.

If you can't see the tracks (some black boards are hard to make them out) then you should get a digital multimeter and set it to continuity mode and probe the pins to see where they lead.

Once you have identified which pin is which you can connect the one that goes to the back light to your Arduino and drive it with PWM.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.