lcd-backlight

#!/bin/bash

LASTPWM=/dev/shm/lcd35
PWMFILE=/sys/devices/platform/pwm-ctrl/duty0

if [ -z "$1" ]; then
        echo "Usage $0 on|off|<0-100>"
        echo "Set the backlight of the LCD on/off or to a percent illumination"
        exit;
fi

if [ "$1" = "off" ]; then
        #save the current value
        cat $PWMFILE > $LASTPWM
        echo 0 > $PWMFILE
        echo "Turned off 3.5in LCD"
        exit;
fi

if [ "$1" = "on" ]; then
        #see if the old PWM value has been saved
        if [ -f "$LASTPWM" ]; then
                cat "$LASTPWM" > $PWMFILE
        else
                #no previous value, turn on full brightness
                echo 1023 > $PWMFILE
        fi
        echo "Turned on 3.5in LCD"
        exit;
fi

if [ "$1" -ge 0 -a "$1" -le 100 ]; then
        #set a percent of brightness
        value=$[1023*$1/100]
        echo $value > $PWMFILE
        echo "Set backlight to $1% ($value)"
fi