Automating the DoorBell via Moteino

A project log for The Moteino Framework

Automation framework based on wireless Moteino nodes.

Felix RusuFelix Rusu 04/15/2015 at 12:420 Comments

I've added my doorbell to the Moteino Framework!
That means I can:

Below is a schematic of what a typical wired door bell circuit looks like, and also a photo of what it looks like in my house. The dotted green rectangle is the circuit that I have physical access to – pictured next to it in my basement (and I don't have a back door button):

I have a single button (front door) and probably most houses do. So I only care to inject my solution for that front door button. There is typically a 16VAC transformer powered from mains that activates the chime when the switch is pressed. So there are a few issues to solve in order to tap into this circuit, detect button presses and also being able to control it via Moteino:

Getting DC from a 16V-AC source and also detecting AC current on a Moteino digital pin are probably the most interesting problems to solve for this project. We can use a H11AA1 chip to detect AC zero-cross, and then manipulate that signal with a transistor and capacitor to get a constant logic "HIGH" that we can read on a Moteino pin (that will detect when the doorbell push button is pressed). Here is the H11AA1 output and the resultant logic HIGH after adding a transistor+cap to invert and smooth the signal:

Here is the whole schematic and installed circuit:

And a graph of doorbell events on the yet-to-be-released Moteino Gateway Interface:

To see the details I explain the build step by step in the detailed blog post.