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Fix brightness control #83

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josch0 wants to merge 1 commit into from
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Fix brightness control #83

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10 changes: 4 additions & 6 deletions drivers/st7701/st7701.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -400,7 +400,8 @@ void ST7701::start_frame_xfer()
// pwm control
if(lcd_bl != PIN_UNUSED) {
pwm_config cfg = pwm_get_default_config();
pwm_config_set_wrap(&cfg, BACKLIGHT_PWM_TOP);
// PWM frequency for CTRL-Pin on AP3031 must be below 1000 Hz for seamless dimming between 0% and 100%
pwm_config_set_clkdiv_int(&cfg, 20);
pwm_init(pwm_gpio_to_slice_num(lcd_bl), &cfg, true);
gpio_set_function(lcd_bl, GPIO_FUNC_PWM);
set_backlight(0); // Turn backlight off initially to avoid nasty surprises
Expand Down Expand Up @@ -665,11 +666,8 @@ void ST7701::start_frame_xfer()
}

void ST7701::set_backlight(uint8_t brightness) {
// At least on my hardware this gives reasonable control over the possible range of backlight brightness
uint16_t value;
if (brightness == 0) value = 0;
else if (brightness == 255) value = BACKLIGHT_PWM_TOP;
else value = 181 + (brightness * brightness) / 85;
float gamma = 1.8;
uint16_t value = (uint16_t)(pow((float)(brightness) / 255.0f, gamma) * 65535.0f + 0.5f);
pwm_set_gpio_level(lcd_bl, value);
}

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1 change: 0 additions & 1 deletion drivers/st7701/st7701.hpp
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Expand Up @@ -47,7 +47,6 @@ namespace pimoroni {
uint lcd_dot_clk = 22;

static const uint32_t SPI_BAUD = 8'000'000;
static const uint32_t BACKLIGHT_PWM_TOP = 6200;

public:
// Parallel init
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43 changes: 43 additions & 0 deletions examples/brightness.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
from presto import Presto
from touch import Button
from time import sleep

presto = Presto()
display = presto.display

FG_COLOR = display.create_pen(0, 0, 255)
BG_COLOR = display.create_pen(255, 255, 255)

touch = presto.touch

button_down = Button(10, 125, 105, 105)
button_up = Button(125, 125, 105, 105)

brightness = 100

while True:
touch.poll()

display.set_pen(BG_COLOR)
display.clear()

display.set_pen(FG_COLOR)
display.text("brightness: " + str(brightness)+ " %", 10, 10)

display.rectangle(*button_down.bounds)
display.rectangle(*button_up.bounds)

if button_down.is_pressed():
brightness -= 1
if brightness < 0: brightness = 0

if button_up.is_pressed():
brightness += 1
if brightness > 100: brightness = 100

presto.set_backlight(brightness / 100)

presto.update()
sleep(0.02)


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