Running a CNC router without a laptop

Most CNC senders quietly assume there's a computer bolted to your workflow. Even the browser-based ones need a host PC or a Raspberry Pi sitting next to the machine. For a lot of hobby setups that's overkill — a whole computer babysitting a controller that only needs a serial connection and someone to press Start.

You can cut the computer out completely. A modern Android phone can connect directly to a GRBL controller and act as both the pendant and the G-code sender. This article explains how that works, what hardware you need, and where the limits are — using Gantry, which supports direct connection out of the box.

Why go computer-free?

• Less to set up and less to break. No OS updates, no driver hunts, no "which COM port is it today" — just a phone and a cable.
• Nothing valuable living in the sawdust. A phone goes in your pocket when you're done.
• Genuinely portable machines. For an MPCNC, a small engraver, or a machine you move around, a phone-only setup is far tidier than dragging a laptop everywhere.

How a direct connection works

There are two physical paths from a phone to a GRBL controller.

USB-OTG (a cable straight to the board)

Most GRBL controllers talk to the outside world as a USB serial device — the board has a USB-to-serial chip (commonly a CH340, CP210x, or FTDI). On a desktop, your OS loads a driver for that chip and the sender opens a COM port.

Android phones that support USB-OTG ("on-the-go") can host that same USB device through a simple OTG adapter or cable. The app opens the serial connection directly — no driver install, no PC in the middle. You plug the phone into the controller, pick the device, and you're connected.

What you need: - A phone that supports USB-OTG (most Android phones from the last several years do; you can check with a free "OTG checker" app or your phone's specs). - A USB-OTG adapter or cable that matches your phone's port (USB-C or micro-USB) on one end and your controller's USB port on the other. - A controller that's powered (many boards are powered by the machine's supply; if yours relies on USB power, make sure the phone can supply it or power the board separately).

Bluetooth (wireless, no cable)

If your controller has Bluetooth, you can skip the cable. Two flavours exist in the GRBL world:

• Classic Bluetooth SPP — the kind you get from an HC-05/HC-06-style module wired to a board's serial pins.
• BLE (Bluetooth Low Energy) — used by some newer boards, and by FluidNC, which has Bluetooth built in.

Pair the controller with your phone, select it in the app, and you have a wireless serial link — the phone jogs and streams over Bluetooth.

Setting it up

1. Decide your path. Have a USB port on the controller and an OTG-capable phone? Use the cable — it's the most reliable. Prefer wireless and have a Bluetooth-capable board? Pair over Bluetooth.
2. Connect the hardware. Plug in the OTG cable, or pair the Bluetooth device in Android settings first.
3. Open the app and select the device. In Gantry's connection panel, choose the USB serial device or the paired Bluetooth device. It connects and the DRO goes live.
4. Confirm the basics. Check the reported status is Idle, jog a small amount, and verify the position updates. Now you're ready to home, zero, and run.

No hardware yet? The built-in simulator lets you learn the whole interface first, then switch to your real controller when it's wired up.

Where the limits are (an honest word)

Direct-connect is genuinely PC-free, but hardware varies, so set expectations:

• Controller compatibility varies. The standard GRBL serial path (GRBL 1.1, grblHAL, FluidNC) is what's supported. An unusual board or an off-brand serial chip may behave differently — worth a quick test with the free app before you commit.
• USB-OTG quality matters. A cheap or worn OTG cable can drop under load. If a connection is flaky, the cable is the first thing to swap.
• Keep the phone awake and charged. A long job needs the screen not to sleep and the battery not to die. A good app keeps the screen awake during a job; plug the phone in for long runs.

The payoff

Once it's set up, the workflow is beautifully simple: walk up to the machine, plug in (or connect over Bluetooth), jog, zero, load a file, and cut — no computer anywhere in the chain. For a lot of hobby CNC work, that's all you ever needed.

If you want to run your machine without a laptop, Gantry is free on Google Play and supports both USB-OTG and Bluetooth direct connections, plus Wi-Fi if you'd rather keep a server running. New to running a CNC from a phone? Start with controlling a GRBL router from your phone.

Safety note: a CNC machine can cause serious injury. Always keep clear of the machine, know where your emergency stop is, and never leave a running job unattended.