Questions about backlight LED

[drzacek]

Hello,

I've been wondering about the backlight LEDs. I dont quite understand the labels on those 4 pins, but I saw some i2c project and saw they just put 3.3V for the upper 2 pins and drive the bottom 2 to GND via mosfet.

Now the questions that I have:

1. Are there any resistors inside the keyboard module? So we can calculate the current and add another resistor for 5V
2. How much current do they drive? Is the transistor really necessary? If it's only few mA I would just sink it to GPIO.

[arturo182]

The labels mean that pin 26 is the anode for LEDs 1 and 2, pin 24 is the anode for LEDs 3 and 4, 25 is the cathode for LEDs 1 and 4, and 23 for 2 and 3.

If you look at the scan of the flex PCB inside, you can see the resistors: https://github.com/arturo182/BBQ10KBD/blob/master/flex_scan.png

I don't have data on the current, but if you have a keyboard you can measure it quite easily.

The MOSFET is probably not needed but I wanted to stay on the safe side since I didn't know which MCU was going to be driving the backlight.