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Forum Index : Microcontroller and PC projects : LCD Backlight Control

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OA47

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Joined: 11/04/2012
Location: Australia
Posts: 926
Posted: 01:26am 09 Apr 2024
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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

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Joined: 12/10/2011
Location: Australia
Posts: 1873
Posted: 01:38am 09 Apr 2024
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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

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Joined: 18/12/2014
Location: Australia
Posts: 896
Posted: 02:14am 09 Apr 2024
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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
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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
 
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