We were recently working with a customer who was using our 10.1″ HDMI display with a Raspberry Pi, but he had run into a problem. When the Raspberry Pi shut down, he needed the display backlight to also turn off and stay off. Since the backlight on the display turns on if uncontrolled, when the signal from the rPi was removed, the backlight came back on.
In order to make this happen, a few changes need to be made to the PCB. Bear in mind that making changes to the PCB will void your warranty, and may damage the display.
Modify the Backlight Circuit to Turn the Display Off
First, the PCB has a pull up resistor that needs to be changed to a pull down resistor. This means the rPi will need to pull the backlight enable (BL_EN) pin high whenever the backlight needs to be on.
- Remove the resistor at RB7. This is the BL_EN pin, we’re going to switch it from pulling up to pulling down.
- Solder the resistor to the RB7 pad closest to DB1.
- Solder the other end of the resistor to ground.
It’s that easy! Just remember that with this change, the BL_EN pin needs to be pulled high in order for the backlight to turn on. On our display, this is controlled via GPIO18 (pin 12). What if you want to switch that pin?
Changing the Backlight Enable Pin
To change which GPIO controls the backlight enable:
- Remove the 0Ω resistor from RB6 (this resistor connects the EN pin to GPIO18, BL_EN).
- Solder one end of a loooong wire to the upper pad of RB6.
- Connect the other end to the GPIO pin of your choice.
Which Displays Will This Work On?
Similar modifications will also work on our other HDMI displays. Find the backlight pull up resistor and switch it to pull down.
If you have any questions, we can be reached at firstname.lastname@example.org, we also provide chat and telephone support Monday through Friday during our open hours.