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.

• 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.

Here.

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:

• Unless otherwise stated, blue-cat refers to the whole project.
• We refer to the blue-cat BLE+GPIO module as cat.
• We refer to the chihuahua BLE+speaker module as dog.