Can an iPad replace an HMI panel?

As an operator screen for monitoring, setpoints and start/stop — yes, with a mount, kiosk mode and permanent power it holds up fine. As a safety device — no: hardwired E-stops and guard circuits stay regardless of what shows the screens. Treat the tablet as the window, never the interlock.

What's the Siemens way to put a Comfort Panel on a tablet?

Enable Sm@rtServer on the panel — it's standard VNC, so any VNC client on the tablet connects and mirrors the panel one-to-one. Know the limits: it needs the panel alive and licensed VNC connections configured, and the newer Unified panels replaced this route with a web client. The alternative is skipping the panel entirely and reading the S7 directly.

Does the tablet need to be on the machine's network?

Yes — both paths need network reach to the panel or PLC. The clean way is a small client-mode Wi-Fi bridge plugged into a spare machine-switch port: the tablet joins that local SSID and sees only the machine network — loop in plant IT where your policy requires.

Is there an Android version of LK Go?

The iPhone/iPad app is free on the App Store; Android is in closed beta on Google Play. The direct-to-PLC architecture is identical — EtherNet/IP with automatic Logix tags, Siemens S7 and Modbus TCP.

Tablet as HMI: mirror the panel or talk to the PLC directly

Using a tablet as an HMI: the two paths and when each works

How-to guide

Every "tablet as HMI" setup is one of two architectures: the tablet mirrors an existing panel (VNC), or the tablet talks to the PLC directly. They fail differently, cost differently, and suit different situations — picking the wrong one is how tablets end up in the drawer. Here's when each works.

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 Go 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 export 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.

Tag browser in LK Go: every tag of a ControlLogix or CompactLogix controller with live values and search, read straight from the PLC — The Logix controller hands over its whole tag list — live, searchable

Temporary operator panel in LK Go mounted as the machine's operator screen: start and stop push buttons, hold-to-run jog, speed setpoint and status lamps — The temporary panel: start/stop, jog, setpoints, status lamps

Guarded setpoint write in LK Go: allowed range shown and confirmation required before the value reaches the ControlLogix PLC — Writes are range-checked and confirmed before they reach the PLC

A temporary screen in minutes

Free app · iPhone & iPad

Zero-config tag browser for Logix, drag-and-drop dashboard, operator panel, alarms — no changes to the PLC logic.

Download on theApp Store

On a desktop? Scan with your iPhone or iPad to get the free app.

See the app tour →

For the machine itself: LineKeeper On is a self-contained 7″ or 10″ touchscreen built to stand on the machine while the replacement panel is repaired or shipped — the same drag-and-drop screens, plus what a phone shouldn't carry:

Live view of every mapped tag, refreshed twice a second — plus per-tag unlocked writes, confirmed and audit-logged
Operator panel: start/stop, indicators, setpoints — hold-to-run releases when your finger lifts (not a safety function)
Stays useful after the repair: data logging, dashboards, machine diagnostics

Small hardware that helps while the panel is out: a Wi-Fi bridge or a USB-C Ethernet adapter to get the phone onto the machine network, a pole-mount arm for the temporary screen, an IP67 box for the bridge. What each one is for, and when you don't need it, is on the gear list.

LineKeeper On, the same idea on a 7″ or 10″ touchscreen that stays on the machine and logs 24/7, is on preorder: 7″ $800, 10″ $900, one-time, no subscriptions. Ships within 8 weeks of order; full refund any time before your unit ships; 30-day money-back after delivery. Keeping the repair history too? LK Up is a free maintenance system that runs on your own PC (early access).