Path 1: mirror an existing panel (VNC)
Many panels can serve their screen over the network: Siemens Comfort Panels via Sm@rtServer (which is standard VNC — any VNC client connects, RealVNC and TightVNC included), Weintek and PanelView Plus units via their built-in VNC servers. The tablet shows the same screens the operator already knows, zero rebuild.
- Wins when: the panel works and you want a second view — monitoring from the mezzanine, a supervisor's walk-around screen.
- Honest limits: the mirror dies with the panel — as a backup plan it's worthless the day the panel goes dark; one more password/VNC port to manage; laggy over weak Wi-Fi; and Siemens' Unified panels dropped the native Sm@rtClient route in favor of a web client.
Path 2: talk to the PLC directly
The tablet runs its own HMI app speaking the controller's protocol — the panel isn't in the loop at all. The free LineKeeper app works this way: EtherNet/IP with automatic Logix tag lists, Siemens S7, Modbus TCP; screens built by drag-and-drop or converted from the panel project with the free in-browser converter.
- Wins when: the panel is dead, obsolete or oversubscribed — this path doesn't care; it's also the honest backup plan, because it works precisely when the panel doesn't.
- Honest limits: screens are rebuilt or converted, not pixel-identical; S7 classic access needs PUT/GET enabled and non-optimized DBs; and no tablet is a safety device — the hardwired E-stop stays.
Making it plant-worthy
- Mount it: a VESA-adapter case on a pole mount puts the screen at eye level — a tablet in a drawer is not an HMI.
- Kiosk it: on iPad, Guided Access locks the device to one app with a passcode; the operator gets buttons, not Safari.
- Power it: permanent USB power from the cabinet (a PoE splitter is the tidy route); batteries are for walk-around use only.
- Network it: a client-mode Wi-Fi bridge into a spare switch port gives the tablet the machine network without touching plant IT — details in the PLC-over-Wi-Fi guide.
- Gloves: capacitive screens and work gloves disagree — either touch-capable gloves or generous button sizes.
The 15-minute temporary panel
Zero-config tag browser for Logix, drag-and-drop dashboard, operator panel, alarms — no changes to the PLC program.
On a desktop? Scan with your iPhone or iPad to get the free app.For the machine itself: the LineKeeper device — in development — is a self-contained 7″ or 10″ touchscreen built to live on the machine permanently — the same drag-and-drop screens, plus what a phone shouldn't carry:
- Live view of every tag, refreshed twice a second — plus write access with a full audit log
- Operator panel: start/stop, indicators, setpoints — hold-to-run buttons release safely
- Stays useful after the repair: data logging, dashboards, machine diagnostics
Small hardware that helps while the panel is out
- GL.iNet Opal travel router — Wi-Fi into the machine network from a spare switch port, so the phone app can stand in as the screen today.
- Anker USB-C to gigabit Ethernet adapter — wired straight into a spare switch port, the phone sees the controller in seconds; USB-C iPhones and iPads need no drivers.
- VIVO pole-mount VESA arm — puts the temporary screen at eye level on a machine post instead of a chair.
- TICONN IP67 enclosure with clear cover — houses the gateway or Wi-Fi bridge on the machine without bare boards on the rail.
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