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

hd44780/hd44780.go

@@ -38,17 +38,17 @@ const (
 //
 // Implements periph.io/conn/x/display/TextDisplay and display.DisplayBacklight
 type HD44780 struct {
-	dataPins     gpio.Group
+	dataPins  gpio.Group
-	resetPin     gpio.PinOut
+	resetPin  gpio.PinOut
-	enablePin    gpio.PinOut
+	enablePin gpio.PinOut
-	backlightPin gpio.PinOut
+	bl        interface{}
-	mode         ifMode
+	mode      ifMode
-	rows         int
+	rows      int
-	cols         int
+	cols      int
-	on           bool
+	on        bool
-	cursor       bool
+	cursor    bool
-	blink        bool
+	blink     bool
-	lastWrite    int64
+	lastWrite int64
 }
 
 const (
@@ -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
@@ -89,14 +90,14 @@ func NewHD44780(
 	}
 
 	display := &HD44780{
-		dataPins:     dataPinGroup,
+		dataPins:  dataPinGroup,
-		resetPin:     *resetPin,
+		resetPin:  *resetPin,
-		enablePin:    *enablePin,
+		enablePin: *enablePin,
-		backlightPin: *backlightPin,
+		bl:        backlight,
-		mode:         mode,
+		mode:      mode,
-		rows:         rows,
+		rows:      rows,
-		cols:         cols,
+		cols:      cols,
-		on:           true,
+		on:        true,
 	}
 	return display, display.init()
 }
@@ -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
+// Set the backlight intensity.
-// pin when creating the display to use this.
 func (lcd *HD44780) Backlight(intensity display.Intensity) error {
-	on := (intensity > 0)
+	switch bl := lcd.bl.(type) {
-	err := lcd.Display(on)
+	case display.DisplayBacklight:
-	if err != nil {
+		return bl.Backlight(intensity)
-		return err
+	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)
 }