Change backlight implementation

hd44780/af_i2c_backpack.go

@@ -43,7 +43,7 @@ func NewAdafruitI2CBackpack(bus i2c.Bus, address uint16, rows, cols int) (*HD447
 	reset, _ := gr.ByOffset(4).(gpio.PinOut)
 	enable, _ := gr.ByOffset(5).(gpio.PinOut)
 	bl := gr.ByOffset(6).(gpio.PinOut)
-	return NewHD44780(gr, &reset, &enable, &bl, rows, cols)
+	return NewHD44780(gr, &reset, &enable, NewBacklight(bl), rows, cols)
 }
 
 // This function returns a display configured to use the SPI side of the Adafruit
@@ -54,7 +54,7 @@ func NewAdafruitSPIBackpack(conn spi.Conn, rows, cols int) (*HD44780, error) {
 	gr, _ := chip.Group(d7, d6, d5, d4)
 	rs := &chip.Pins[rsPin]
 	e := &chip.Pins[enablePin]
-	bt := &chip.Pins[backlightPin]
+	bl := &chip.Pins[backlightPin]
 
-	return NewHD44780(gr, rs, e, bt, rows, cols)
+	return NewHD44780(gr, rs, e, NewBacklight(bl), rows, cols)
 }

hd44780/backlight.go

@@ -0,0 +1,34 @@
+// Copyright 2025 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package hd44780
+
+import (
+	"periph.io/x/conn/v3/display"
+	"periph.io/x/conn/v3/gpio"
+)
+
+// A monochrome backlight  Implements display.Backlight It uses a single
+// GPIO Pin to turn the backlight on or off.
+type GPIOMonoBacklight struct {
+	blPin gpio.PinOut
+}
+
+// Given a GPIO pin that turns the backlight on/off, construct a monobacklight
+// to use with HD44780.
+func NewBacklight(blPin gpio.PinOut) *GPIOMonoBacklight {
+	return &GPIOMonoBacklight{blPin: blPin}
+}
+
+// Turn the display backlight on or off.
+func (bl *GPIOMonoBacklight) Backlight(intensity display.Intensity) (err error) {
+	if intensity == 0 {
+		err = bl.blPin.Out(gpio.Low)
+	} else {
+		err = bl.blPin.Out(gpio.High)
+	}
+	return err
+}
+
+var _ display.DisplayBacklight = &GPIOMonoBacklight{}

hd44780/example_test.go

@@ -44,8 +44,8 @@ func Example() {
 	pins := ls.Pins()
 	reset := pins[4].(gpio.PinOut)
 	enable := pins[5].(gpio.PinOut)
-	bl := pins[6].(gpio.PinOut)
-	lcd, err := hd44780.NewHD44780(ls, &reset, &enable, &bl, 2, 16)
+	bl := hd44780.NewBacklight(pins[6].(gpio.PinOut))
+	lcd, err := hd44780.NewHD44780(ls, &reset, &enable, bl, 2, 16)
 	if err != nil {
 		log.Fatal(err)
 	}

hd44780/hd44780.go

@@ -41,7 +41,7 @@ type HD44780 struct {
 	dataPins  gpio.Group
 	resetPin  gpio.PinOut
 	enablePin gpio.PinOut
-	backlightPin gpio.PinOut
+	bl        interface{}
 	mode      ifMode
 	rows      int
 	cols      int
@@ -80,7 +80,8 @@ func getRowConstant(row, maxcols int) byte {
 // connected using all 8 pins.
 func NewHD44780(
 	dataPinGroup gpio.Group,
-	resetPin, enablePin, backlightPin *gpio.PinOut,
+	resetPin, enablePin *gpio.PinOut,
+	backlight interface{},
 	rows, cols int) (*HD44780, error) {
 
 	mode := mode4Bit
@@ -92,7 +93,7 @@ func NewHD44780(
 		dataPins:  dataPinGroup,
 		resetPin:  *resetPin,
 		enablePin: *enablePin,
-		backlightPin: *backlightPin,
+		bl:        backlight,
 		mode:      mode,
 		rows:      rows,
 		cols:      cols,
@@ -277,18 +278,29 @@ func (lcd *HD44780) Halt() error {
 	return lcd.dataPins.Halt()
 }
 
-// Turn the display's backlight on or off. You must supply a backlight control
-// pin when creating the display to use this.
+// Set the backlight intensity.
 func (lcd *HD44780) Backlight(intensity display.Intensity) error {
-	on := (intensity > 0)
-	err := lcd.Display(on)
-	if err != nil {
-		return err
+	switch bl := lcd.bl.(type) {
+	case display.DisplayBacklight:
+		return bl.Backlight(intensity)
+	case display.DisplayRGBBacklight:
+		return bl.RGBBacklight(intensity, intensity, intensity)
+	default:
+		return display.ErrNotImplemented
 	}
-	if lcd.backlightPin != nil {
-		err = lcd.backlightPin.Out(gpio.Level(on))
+}
+
+// For units that have an RGB Backlight, set the backlight color/intensity.
+// The range of the values is 0-255.
+func (lcd *HD44780) RGBBacklight(red, green, blue display.Intensity) error {
+	switch bl := lcd.bl.(type) {
+	case display.DisplayRGBBacklight:
+		return bl.RGBBacklight(red, green, blue)
+	case display.DisplayBacklight:
+		return bl.Backlight(red | green | blue)
+	default:
+		return display.ErrNotImplemented
 	}
-	return err
 }
 
 // delayWrite looks at the time of the last LCD write and if

hd44780/pcf857x_backpack.go

@@ -46,5 +46,5 @@ func NewPCF857xBackpack(bus i2c.Bus, address uint16, rows, cols int) (*HD44780,
 	reset := grPins[4].(gpio.PinOut)
 	enable := grPins[5].(gpio.PinOut)
 	bl := grPins[6].(gpio.PinOut)
-	return NewHD44780(gr, &reset, &enable, &bl, rows, cols)
+	return NewHD44780(gr, &reset, &enable, NewBacklight(bl), rows, cols)
 }