With the launch of iOS & iPadOS 13, iPhone and iPad now have the ability to edit code on CircuitPython USB devices. Users can connect a board such as Circuit Playground Express to their mobile device and edit & run code on the go.

For this guide, we'll be using a Circuit Playground Express, but the process should work with any of Adafruit's CircuitPython USB devices - click here for a full list.

What you'll need

• An iPhone capable of running iOS 13 or iPad capable of running iPadOS. Check your device's compatibility here.

If you're using an iPad Pro equipped with a USB-C port, skip the Lightning Adapter & USB A to Micro-B cable and simply use a USB-C to Micro-B cable:

First, let's check to make sure your CircuitPython & Apple devices are ready to talk to eachother.

Update CircuitPython

At the time of this writing iOS & iPadOS have been tested and confirmed to work with CircuitPython version 4.1.0.

Connect your CircuitPython compatible device to your computer (not the iOS device), and open the boot_out.txt file and check what version of CircuitPython you're running. 

If you don't see a file named boot_out.txt or you have an older (than 4.1.0) or alpha version of CircuitPython installed, update to the latest stable release using these instructions.

Update iOS/iPadOS

On your iPhone/iPad, check what version OS you're running by opening the Settings app and tapping General->About and checking the Software Version number.

If your version number is 13 or later, you’re good to go. If not, update your OS via Settings->General->Software Update. 

Connect CircuitPython device to iPhone/iPad

For devices with a Lightning connector – connect your Lightning to USB Adapter to iPhone/iPad and connect your CircuitPython device to the adapter via a micro USB cable.

For devices with a USB-C connector – connect your CircuitPython device directly to your iPad using a USB-C to Micro-B cable.

Copy code from CIRCUITPY drive

Plug your CircuitPython board, via USB, to your iDevice using the appropriate cable.

On your iDevice, open the Files app, and tap on the drive labelled CIRCUITPY. Locate the code.py file within. Tap and hold on code.py and choose Copy from the menu.

Paste code to internal storage

Next in the Files app, navigate back and tap On My iPhone/On My iPad.

Tap and hold on an empty area, and choose Paste from the menu.

Edit code

Open the App Store and search for the free app named Koder Code Editor and download/install it.

Open Koder and tap the new file icon in the lower left hand corner, tap Open Other App’s Files, then open the internal copy of code.py stored in On My iPhone/On My iPad.

Make changes to your code, then close the file – it will be saved automatically.

Overwrite original code.py on CIRCUITPY

Return to the Files app and navigate to On My iPhone/On My iPad. Tap and hold on the edited code,py file, and choose Copy from the menu.

Navigate to the CIRCUITPY drive, tap and hold in a blank area, choose Paste from the menu, and then choose Replace from the popup that appears.

Done

After a few seconds, your CircuitPython device should restart and begin running your new code. That’s all there is to it - enjoy the world of mobile embedded development!