Home
JAQForum Ver 24.01
Log In or Join  
Active Topics
Local Time 20:30 25 Nov 2024 Privacy Policy
Jump to

Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.

Forum Index : Microcontroller and PC projects : LCD Backlight Control

Author Message
OA47

Guru

Joined: 11/04/2012
Location: Australia
Posts: 926
Posted: 01:26am 09 Apr 2024
Copy link to clipboard 
Print this post

Reading the Pi Pico manual and the section on LCD backlight:
  Quote  Backlight Control
For the ILI9163, ILI9341, ST7735, ST7735S, SSD1331, ST7789, ILI9481, ILI9488, ILI9488W, ST7789_135 and
ST7789_320 displays an optional parameter ‘, backlight’ can be added to the end of the configuration parameters
which specifies a pin to use to control the brightness of the backlight. This will setup a PWM output on that pin
with a frequency of 1KHz and an initial duty cycle of 99%.
You can then use the BACKLIGHT command to change the brightness between 0 and 100%. The PWM channel
is blocked for normal PWM use and must not conflict with the PWM channel that may be set up for audio.
For example:
OPTION LCDPANEL ILI9341, OR, DC, RESET, CS, GP11


Do I need to use a transistor to intertface from the Pico to the LCD or can I connect directly from the GP to the LED pin?

0A47
 
palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 1873
Posted: 01:38am 09 Apr 2024
Copy link to clipboard 
Print this post

I use the circuit from the Micromite Backpack, look on Geoff's site.
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
disco4now

Guru

Joined: 18/12/2014
Location: Australia
Posts: 896
Posted: 02:14am 09 Apr 2024
Copy link to clipboard 
Print this post

It will depend on the LCD Panel. The earlier ILI9341 only exposed the backlight LED Anode (LED-A) so you need to supply enough current hence a transistor. Most now expose the BL pin as a logic level and can be driven  directly. On the ILI9341 inspect the LCD and see if the BL pin heads towards a resistor and transistor.
I think the ILI9488 have BL going to R6 and Q1 so only a logic level is required.
Latest F4 Latest H7
 
OA47

Guru

Joined: 11/04/2012
Location: Australia
Posts: 926
Posted: 04:25am 09 Apr 2024
Copy link to clipboard 
Print this post

Thankyou Disco4now, the LCD panel I am using is indeed an ILI9488 and I traced the PIN labelled BL to a transistor circuit so I connected it to a PWM pin and all works fine.

0A47
 
Print this page


To reply to this topic, you need to log in.

© JAQ Software 2024