A 30 second idle timeout sits below the whole-minute range most built-in backlight savers cover, so build it in logic: an on-delay timer preset to 30 seconds, a panel-control write that switches to a one-button screen and sets backlight intensity to 0%, and a touch action that restores the screen, the light and the timer. The wake touch only works if the button is on the screen shown while dark.
Yes, a panel can go dark after 30 seconds with no touches and come back on the first one, but on most HMI families the 30 second part is your logic, not a setting. Built-in backlight savers usually step in whole minutes. The design that works: an on-delay timer preset to 30 seconds in the PLC, a panel-control write that switches the panel to a screen holding one full-screen button and drops the backlight to 0%, and a touch action that brings back the screen, the light and the timer. One rule decides whether the whole thing works: the touch target has to sit on the screen shown while the panel is dark. A dark panel whose active screen has no configured button ignores your finger. Here is the build, the checks and a worked timing example.
Check the built-in backlight saver first
Open the panel's configuration software and look for an inactivity or backlight-saver setting before you write any logic. Some configuration packages document one directly: an inactivity timer that turns the backlight off after a set idle time. The presets are usually whole minutes. One common panel family documents a range of 1 to 255 minutes, so the shortest preset is 60 s, twice your 30 second target. Read what the setting controls, too: some panels use their idle timer to log the current user off a secured screen, which is a logout, not a backlight switch.
Decision: if the built-in setting reaches 30 seconds or less and a touch is confirmed to restore the light, use it and stop here. Below one minute, build the timer in the PLC. The built-in preset path is covered in Set the HMI backlight saver timeout on a PLC panel.
What you need
- An on-delay timer in the PLC, or in the project's macro layer, preset to 30 seconds.
- The panel-control write your project tool provides for screen changes and backlight control, often listed as a PLC-to-panel function; one project tool writes it as
PLC-->Panel. - A spare screen to serve as the dark screen.
- One button object sized to cover the whole display.
- An activity tag that the panel writes when an operator touches it.
The wake button must be on the dark screen
Turning the backlight off leaves the panel running its active screen. What wakes it is a touch on a configured object on that screen. If the panel goes dark on a read-only screen, a blind touch lands on nothing and the light stays off. So the dark state gets its own screen: a plain surface with one button stretched across the display. Nothing on it needs to be readable, because the backlight is at 0% while it is up. The button exists to be touched.
If you also want the panel to wake itself for a shift start or a scheduled message, pair this design with Wake an HMI screen from screen saver on a PLC schedule, which drives the same screen change from the PLC's clock.
Build the cycle
- Time the idle. Run an on-delay timer with a 30 second preset, 30 000 ms on millisecond timers. Reset its accumulator every time the panel writes a value an operator caused: a setpoint entry, a screen selection, the wake touch. If your project tool runs a macro on every screen change, put the reset in that macro once and it covers every screen.
- Make the dark screen. New screen, one button sized across the display, no text that has to be read.
- Write the idle action. When the timer's done bit is on, send two panel-control writes in order: change screen to the dark screen, then set backlight intensity to 0%. Where the tool exposes intensity it is a 0 to 100% value; one common family documents the set as a register called
SI 9and the restore of the previous value asSB 16. Screen first, light second, so the wake button exists before the panel goes dark. - Write the wake action. One touch on the dark screen's button does three things: change screen back to the operating screen, set the intensity back to 100% or restore the previous value, and pulse the activity tag so the timer restarts from zero.
- Gate on alarms. Fire the idle action only while no alarm bit is active. An alarmed panel stays lit until the condition clears, which keeps the alarm readable.
- Clear the pulse. Set the activity tag to 1 in the touch action and clear it on the next scan, so each idle period measures from the last real touch.
The screen-change write itself has one quirk worth knowing: what happens when the target screen number is already the active screen. PLC to panel screen switch register: retrigger the same screen covers that case.
Example: one 30 second dark cycle, then a full shift
Scenario: an order-status panel at a pack station. Operators touch it 12 times over an 8 hour shift, an average gap of 40 min between touches: 12 × 40 min = 480 min = 8 h. Idle preset: 30 s.
Walk one gap. The last touch lands at 07:42:10 and resets the accumulator to 0. The accumulator reaches 30 s at 07:42:40, the done bit fires the two writes, and at a typical PLC scan time of 1 to 10 ms the panel is on the dark screen at 0% intensity by 07:42:41. It sits dark until the next touch at 08:15:22, which is 32 min 41 s of dark (08:15:22 − 07:42:41 = 32 min 41 s). The wake write returns the operating screen and full intensity by 08:15:23.
Now the whole shift. Each 40 min gap is lit for the 30 s grace and dark for 39.5 min, so dark time is 12 × 39.5 min = 474 min = 7 h 54 min, and 474 / 480 = 98.75% of the shift. Those hours put no lit hours on the backlight, because backlight life ratings count hours the lamp is on.
How to check it worked
- Dark timing. Note the clock at the last touch and at the moment the panel goes dark. The gap must read 30 to 31 s: preset plus one scan.
- Reset proof. Leave the panel idle for 29 s, then touch it. It must stay lit for another 30 s. If it goes dark about 1 s after the touch, the touch never reset the timer.
- Wake. Touch the dark screen once. The operating screen and the light must return within about a second. Repeat five times.
- Navigation. After a wake, open every screen once. The screen-change writes must have left normal navigation working.
- Alarm gate. Raise a test alarm and hold the panel idle past 30 s. It must stay lit.
If the light comes back slowly after a wake, HMI screen slow to light after screensaver wake lists the likely causes and the order to check them.
Recommendation: for any idle target under one minute, run the timer in the PLC and use the one-button dark screen described here, because the built-in savers that publish their range start at 60 s. If your target is one minute or longer and the panel's built-in saver wakes on touch when you test it, use the built-in setting and skip the logic.
Questions
Can I dim the panel partway instead of dropping the backlight to 0%?
Yes. Where the panel exposes intensity as a 0 to 100% value, an idle value of 10% keeps the screen faintly readable and wakes instantly, because the light never fully leaves. Use 0% when a dark panel is the point, for example in a control room or on a bedroom wall. The wake logic is identical either way: same dark screen, same full-screen button, same touch action.
What happens if an operator touches the panel while it is already awake?
Nothing special. Any touch that writes a value resets the accumulator to 0, so the 30 second clock restarts from that touch. The case to design against is a read-only screen: objects that only display values never write, so the panel goes dark 30 seconds after the last write even with someone watching. Put one small activity write on read-only screens, through an invisible button or the screen-change macro.
Why not just use the panel's own screen saver?
A screen saver is the panel's own idle layer. It blanks or animates on the panel's terms, and its wake behavior is not something your project controls, so you can end up back at the blind-touch problem. The one-button dark screen puts the dark state and the wake action inside your project, where the touch target, the screen change and the light are all writes you set. Check the built-in saver first anyway: where it reaches your target time and wakes reliably, it is less logic to maintain.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.