blue-cat

A module to add some smartness in an old doorbell system; and a little bit beyond the module.

The doorbell system suffers from the following problem:

Too mechanical: it rings only as long as a guest has the button pressed. As soon as they release the button, the ringing stops.
Volume too low: cannot hear it clearly a little far away from the doorbell control panel. Furthermore, there is no near-by power plug to the doorbell control panel.

Design

The blue-cat module itself:
- battery-powered (like CR2032, not beefy LiPos);
- simply listen to the doorbell ringing via GPIO;
- when ringed, send out a notification via BLE to another, less location-constraint module called chihuahua.
The chihuahua module:
- wall-powered;
- when notified by blue-cat, plays a ringtone of at least some length;
- keep a track of ring history.

Some "natural" choices:

The blue-cat module: nRF52840-based, with a custom PCB to sense (1) the doorbell voltage driving the speaker; and (2) the battery level.
The chihuahua module: ESP32-C3-based, connecting to a speaker via some I2S-based module.
- The ring history can be exposed as some web-server in the intra-net via WiFi.
The BLE connection between them needs some security attention.
Zephyr as the development platform.
- It should support nRF very well.
- Though might be a little bumpy for the ESP (some basic features still missing, so maybe the support is not very mature?). Backup plan is to use ESP's SDK.

Since blue-cat is both the project name and the name of one of the two boards/apps, we do the following as a distinguishing: