Backlight and Contrast Control in the HMI500 Series

Solution

Backlight Feature

This backlight feature, if enabled, will cause the HMI screen to go blank after the specified time in minutes; the range is 1 to 255 minutes. If this time is set to zero, this feature is disabled and the backlight will always stay ON under normal operation. This feature can be enabled from the EasyBuilder Edit menu, then select System Parameters, then select the General tab. On this window, shown below, find the Backlight Saver on the right hand side.

If the back light saver is enabled and the back light will turns off, the first time someone touches the screen, the back light timer will be reset and the back light will turn ON (no control object will activate during this first touch). Operators will have to press the screen again, after the screen is displayed, in order to initiate some function.

NOTE: If the HMI detects an alarm condition (if the PLC sets an alarm bit ON or if the HMI senses a PLC register has gone out of it normal range and into an alarm condition) the HMI will NOT automatically exit the back light saver mode. In other words, if the HMI back light saver has timed out and an alarm is detected, the screen will remain blank until someone touches the screen.

The PLC can force the HMI out of the back light saver mode by transitioning a bit from ON to OFF. A “PLC
Control Object” is set up in the HMI for “Back light control”. The PLC can set this bit ON for a second or two and then when this bit is transitioned from ON to OFF, the HMI screen will be displayed. If the HMI screen is displayed and this bit is transitioned from OFF to ON, the HMI screen will go blank (as though the Back light saver timer completed timing).

Two PLC control objects can be used to control the backlight saver function. There is a “Back light control” bit that can be used and a “Back light Control (write back)”.

The “Back light control” bit functions according to the table below:

	If a screen is displayed	If NO screen is displayed (back light has been activated due to time out or to previous PLC control)
Back light control bit (i.e. bit B3:0/01 of an Allen Bradley PLC) OFF to ON transition	Screen goes blank (back light turns off)	No action (screen remains blank)
Back light control bit (i.e. bit B3:0/01 of an Allen Bradley PLC) ON to OFF transition	No action	Screen is immediately displayed (back light timer is reset)

The “Back light control (write back)” bit functions according to the table below:

	If a screen is displayed	If NO screen is displayed (back light has been activated due to time out or to previous PLC control)
Back light control (write back) bit (i.e. bit B3:0/13 of an Allen Bradley PLC) OFF to ON transition	Screen goes blank (back light turns off)	No Action
Back light control (write back) bit (i.e. bit B3:0/13 of an Allen Bradley PLC) ON to OFF transition	If this bit is ON, the screen can’t be taken out of back light mode (touching the screen will display a screen but the screen will immediately go blank). The back light timer is forced to time out.	No Action

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Contrast Adjustment

The screen contrast for the HMI5XX-005 models is via a potentiometer located on the back of the HMI. For the HMI5XX-006 models, the contrast is controlled with buttons on the front of the panel. If a panel has an application running, you can get to the RDS mode either by flipping dipswitch 2 up and then pressing the reset button or by using EasyManager to switch to RDS mode. Either method will bring up a screen that allows the contrast to be increased or decreased.

The contrast can also be changed while an application is running. To lighten the contrast, create a Set Bit Object with the address LW9091; select Momentary as the attribute style and label this “Lighter”. This button may need to be pressed 10 times or more to notice the screen become lighter. To darken the contrast, create a Set Bit Object with the address LW9092; select Momentary as the attribute style and label this “Darker”. This button may need to be pressed 10 times or more to notice the screen become darker.