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Example: LCD backlight auto-off timers

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Example: LCD backlight auto-off timers

The white LED backlight used in certain LCD displays has a lifetime of about 3000 hours at full operating current (longer at reduced currents). This is an inherent limitation of the white LED technology (2009). It is therefore advisable to turn off or dim the backlight when not in use.

This page contains several examples for either totally turning off or dimming the backlight after a certain time with no detected user activity. The light comes back on whenever a front panel button is pushed. Which of the examples you follow depends on:

Example 1: Simple on/off for MS120 and MS12 using MultiTrack

The following program code will provide a simple auto-off timer for the MS120 or MS12 backlight. It turns on the backlight whenever a front panel button is pressed, and turns it off again 10 minutes after the last button press. This is designed as a MultiTrack task. This will work in any firmware that supports MultiTrack, providing your program already uses MultiTrack. All MS120s support MultiTrack. The MS12 requires firmware V3.13 or later. For more information see reFlash: How do I determine what version firmware is in my controller?

Your program's initialisation code must contain a GoSub BKLT_Init.

BKLT_Init:      LaunchTask      BKLT_Set0

BKLT_Set0:      On              20      ;Turn On backlight
                InputFM         12      ;Get the front panel buttons
                LoadX           %11111  ;select the 5 bits representing buttons
                GoIfT           BKLT_Set0       ;G/ any button pressed
                LoopIfTiming    60000,BKLT_0    ;Test for timeout, loop if not yet
                Off             20      ;Turn Off backlight
                InputFM         12      ;Get the front panel buttons
                LoadX           %11111  ;select the 5 bits representing buttons
                GoIfT           BKLT_Set0 ;G/ any button pressed
                GoTo            BKLT_1

Example 2: Dimmed backlight for MS120 with suitable firmware and MMi202 with suitable firmware and hardware.

If the MS120 has firmware V3.20 or later it incorporates a simple "set and forget" dimming mechanism.

If the MMi202 contains firmware V3.21 or later and it is fitted with a dimmable LCD, it supports the same "set and forget" dimming mechanism.

Your program can simply run the following code just after turn-on (i.e. in its initialization code) and the dimming will happen automatically:-

BL_HighLevel:   EQU        8    ;"Bright" level, 0 to 8, 8 = 100%
BL_LowLevel:    EQU        1    ;"Dimmed" level, 0 to 8, 1 = 12.5%
BL_DimTime:     EQU        30   ;Timer value, in minutes

                OBLCD_Type 2    ;MUST be done before the dimmer stuff!!. Not required in MS12x
                SetU       0,BL_HighLevel    
                SetU       1,BL_LowLevel
                SPxCmd2    1,!cpu  
                SetU       0,BL_DimTime
                SPxCmd1    4,!cpu

Note that BL_HighLevel and BL_LowLevel must be between 0 (fully off) and 8 (fully on). Any other value will generate an error. BL_DimTime can be 0 to 255. 0 will cause the backlight to dim immediately. 255 will give 4 hours and 15 minutes.

With this mechanism the front panel push buttons are monitored automatically (you don't have to do anything). Whenever a button is pressed it sets the backlight to BL_HightLevel and starts the timer. Every subsequent button press restarts the timer. If the timer expires the backlight is set to BL_LowLevel.

Example 3: Automatic detection of MS12 or MS120 and firmware version

This example lets your program automatically determine if it is running in an MS12, an MS120 with old firmware or an MS120 with newer firmware able to support backlight dimming, then initialize the display accordingly.

BL_Init:        SPxPoll2        3,!CPU       ;get board type
                pushu           1
                GoIfXLT         53,BL_Old    ;MS12 is type numbers 48-52
BL_ms120:       SpxPoll2        0,!CPU       ;Get Firmware Number 
                pushu           0
                goifxgt         3,BL_New     ;Firmware is V4.x (something later than this code!)
;There has never been a firmware lower than 3.x, so assume 3.x and test the release number x
                pushu           1		
                goifxge         20,BL_New    ;3.20 and later support dimming

BL_Old:    initialize non-dimmable backlight
                goto            BL_Finished     

BL_New:    initialize dimmable backlight

BL_Finished: ' ... continue ...