Node-RED notifications on the TV

With the node-red-contrib-telegrambot palette, any flow can send a message to a "Home" group. Enable the overlay on that group in Tevegram and the flow's messages appear over the TV picture. The payload format is the only thing to get right.

Does it work on my TV?

What you need

Node-RED with node-red-contrib-telegrambot installed (Manage palette, Install).
A Telegram bot token from @BotFather (/newbot), the bot added to a dedicated "Home" group, and that group's chat id (send a message in the group and forward it to @getidsbot, or read the "chat":{"id"} field from https://api.telegram.org/bot<TOKEN>/getUpdates; group ids start with -100).
An Android TV or Google TV with Tevegram signed in to the account that is a member of the "Home" group.

Setup

Add a Telegram sender node. Drag a "sender" node from the Telegram category, create a bot configuration with the token, and deploy once so the bot connects.
Build the payload in a function node. The sender expects msg.payload with chatId, type and content, as in the excerpt. Wire your trigger (a sensor, an MQTT topic, a schedule) into the function, then into the sender.
Enable the overlay on the "Home" group in Tevegram. On the TV, in the Chats tab, select the "Home" group and turn on its notification bell. Allow "Display over other apps" when Android asks. From now on, every message posted in that group appears over the TV picture.
Test. Trigger the automation, or type a message in the group from your phone. It should appear on the TV within a second or two, then fade out.

Configuration

Function node feeding the Telegram sender node

msg.payload = {
  chatId: -1001234567890,   // "Home" group
  type: 'message',
  content: 'Washing machine finished'
};
return msg;

Good to know

Photos and formatting

type can also be "photo" with content pointing to an image; it lands in the conversation, while the overlay shows text. Markdown is supported through options: { parse_mode: "Markdown" }, but plain text reads best on a TV.

Frequently asked questions

Does the TV need to be on Tevegram?

No. Tevegram runs in the background and draws the overlay over whatever is on screen: live TV, another app, the home screen. Open it once after the TV has been turned on if notifications stop appearing.

Will my other chats interrupt the TV too?

Only if you turn their bell on. Keep the overlay enabled on the "Home" group alone and the TV shows nothing else.

Home Assistant with Node-RED add-on: which one should send?

Either works. If your automations live in Node-RED, send from Node-RED; if they live in Home Assistant, use its notify service. Avoid doing both for the same event, or the TV shows it twice.