MeshCore - Child Mode

Child mode is a build of MeshCore's companion radio for kids. I made it because we don't want to give our son a phone yet, but still want to reach him and know roughly where he is when he's out. A feature phone has no GPS; a smartphone is too much. This is the middle ground: one small LoRa device he can operate, doing messaging and location over the radio.

Everything child-specific is behind a CHILD_MODE compile flag, so a normal MeshCore build is byte-for-byte identical and we keep tracking upstream. For the mesh itself, see the upstream repo and docs.meshcore.io.

Tested on the Seeed Wio Tracker L1 Pro (nRF52840, 128×64 OLED, joystick + back button). Other nRF52 + screen boards need their own variant but should be easy. I currently don't have another device to test.

What the kid sees

A big clock and a battery icon. Press in for a short menu: read messages, send a quick reply. The full companion UI is compiled in but locked behind a PIN.

Screenshots

Home clock + battery	New message wakes the screen & alerts	Reader scrollable message
Inbox unread •, DM/group icons	Question pick an answer	Call bell “press = I’m here”
Menu messages · send · settings	Send pick a canned message

What it does

• Read messages. DMs and group messages are stored on-device, scrollable, with unread markers and a wake-up notification. Opening one sends a read-receipt back (as a message).
• Questions. Send ?Dinner | Pizza | Pasta; the kid picks an answer and it comes back to you. This is the most important feature for me personally.
• Canned replies. The kid picks from a short list you set ("I'm OK", "On my way"), chooses a recipient, sends.
• Call bell. Send a single 🔔 and the device rings and shows "Dad is calling". The kid presses a key, you get "👋 here" back.
• Location and battery. It's a real MeshCore node, so you can request the kid's position and battery from your phone. Enabled per-contact during setup.
• No strangers. Unknown nodes aren't auto-added, there's no public channel seeded, and stray adverts can't buzz the device. Only contacts you add can reach it.
• Retries on its own. Different from a stock companion radio. See delivery below if you're interested. But the gist is, it tries harder to make sure packages arrive.

Controls are the same everywhere: up/down to move, right or press to choose, left or back to go back.

Install

Grab the latest WioTrackerL1_companion_radio_child-*.uf2 from Releases, then:

1. Plug the L1 into USB.
2. Double-tap reset. It mounts as a USB drive.
3. Drop the .uf2 onto it. It reboots into child mode.

Or build it yourself.

Setting it up (phone needed once)

The device only talks to contacts it knows, and adding them needs a phone — once. Connect the MeshCore app to the kid's device over Bluetooth (unlock with the PIN, default 1234), then:

1. Add each parent as a contact. This isn't automatic — pair each one so their key is stored on the device.
2. Allow location/telemetry requests from those contacts, or requesting the kid's position later won't work.

Add the kid as a contact on each parent's phone too. After that, everything runs over the radio.

Commands (from a parent's phone)

Message the device to control it. These are handled silently — the kid never sees them:

Command	What it does
!pin <old> <new>	Change the lock PIN (default 1234), e.g. !pin 1234 4680.
!tz <minutes>	Clock UTC offset in minutes. Berlin summer !tz 120, winter !tz 60. No automatic DST.
!preset <n> <text>	Set canned-message slot n (1–10), e.g. !preset 1 I'm on my way. Empty clears the slot.
!name <newname>	Rename yourself on the kid's device (DM contact + group messages).
!retry on / !retry off	Turn on-device send retry on or off.
?q | a | b	Ask a question, e.g. ?Dinner? | Pizza | Pasta.
🔔	Rings the device and shows a "calling" screen.

Most of this works in a group channel too, but reliable delivery and location are DM-only. DM the kid when it matters.

Using it (the kid)

• New message: screen lights up, press to read, up/down to scroll.
• Question: up/down to highlight, press to send.
• Send: menu → Send → pick a message → pick who. Shows "Sent"; a failed send stays put to retry.
• Call: press anything to answer, they get a "here".
• The PIN screen opens the full radio, for parents.

Delivery

A stock companion radio leans on its tethered phone app to resend messages that don't arrive. The kid's device has no phone, so it does this itself: it holds each DM until the delivery ACK comes back, otherwise it resends with growing backoff. Overhearing any radio traffic nudges pending messages to resend sooner (rate-limited to every few seconds), and hearing the recipient's own advert triggers an immediate retry that re-floods to relearn the route.

Group messages have no ACK, so they aren't retried — prefer DMs. Turn it off with !retry off.

Building from source

A PlatformIO project. With the repo cloned:

export FIRMWARE_VERSION=v1.7.6.0      # baked into the build
pio run -e WioTrackerL1_companion_radio_child -t upload

Debug build, which traces the retry/ack/flood logic over serial (115200):

pio run -e WioTrackerL1_companion_radio_child_debug -t upload
pio device monitor -e WioTrackerL1_companion_radio_child_debug

Package the .uf2/.zip like a release does:

export FIRMWARE_VERSION=v1.7.6.0
sh build.sh build-firmware WioTrackerL1_companion_radio_child   # lands in out/

Releases and versioning

CI (release-child-firmware.yml) publishes a release on tag push:

git tag child-v1.7.6.123 && git push origin child-v1.7.6.123

Versions are <meshcore version>.<our number> — 1.7.6.123 is our build 123 on MeshCore 1.7.6. Tags are child-v<version>.

Other boards and tests

Other boards and roles build as upstream; nothing here touches them. The plain build for this board is WioTrackerL1_companion_radio_ble (identical to upstream with CHILD_MODE off). sh build.sh list shows every environment.

Hardware-independent logic (config, commands, message store, retry queue, presets, questions, UI widgets) has host tests:

pio test --environment native --verbose

AI Disclosure

It's mixed. I use AI a lot at work. Side projects are a way for me to keep my programming skills alive. This project contains a mix of manually written and AI generated (but manually reviewed) code. I used it more heavily in brainstorming ideas and discovering the original codebase. Don't use this if you're a purist.

Credits

Built on MeshCore by Scott Powell (ripplebiz) and contributors — child mode is a thin layer on top, no extra dependencies, same MIT license. For the mesh itself: MeshCore Discord and docs.meshcore.io.