Doorbell Gateway MQTT Publisher

Introduction

This is a DIY ESP8266-based doorbell detector and gateway.

(It is similar to the older project doorbell-gateway but it also provides a graphical OLED display.)

The idea is that a microphone and a small pre-conditioning circuit prepares an analogue signal to be sampled and converted to digits by the controller (by its integrated analog-digital converter, ADC). The digital voltage signal is then subtracted by a user-defined offset and a simple algorithm is used to detect the ring of the doorbell by setting an amplitude threshold.

On every ring the software posts a configurable MQTT message which can then be used to switch on a buzzer, blink some LEDs, send you an email or a notification on your smartphone, ... - ideas are endless.

The code has been written in the Arduino IDE as it provides simple, ready-to-use libraries.

Hardware setup

I've been using an ESP-12E (NodeMCU 1.0) which uses an ESP8266. Other boards might be compatible as well.

The additional signal conditioning circuit is based on the Claplight MKII 2017 (PCB and parts in a kit) made by kitbuilding.org. The kit can be bought for ~4 € from their web-shop (they sell other great soldering kits, too!).

This part of the schematic is based on an 2N3906 PNP bipolar transistor:

The kit is originally powered by a 9V battery. Instead of using an additional battery, the supply voltage can be connected to the 3V3 pin of the NodeMCU board directly, too - also thanks to the voltage divider R5/R6 where you can lift the mid-supply to an arbitrary value. The GND signal also needs to be connected to the NodeMCU board. The NodeMCU board itself can be powered by a USB power supply or power bank.

The analog trigger signal is connected to the analog input signal pin AD0 of the NodeMCU board.

The hardware setup looks like the following:

Software setup

Sensor software setup

Please change the settings in the file config.h according to your local setup:

• WiFi settings
  • SSID
  • Password
• MQTT settings (the sensor acts as an MQTT publishing client only)
  • Server (IP or hostname)
  • Port
  • Topic
  • Message to be sent on connect event
  • Message to be sent on doorbell detection event
• Hardware-specific settings
  • Pin number of analog input pin
  • Sensor loop delay/ query interval
  • Sensor offset voltage
  • Sensor threshold voltage
  • Sensor detection threshold

Then open the .ino file in the Arduino IDE, re-compile and upload it to your target uC.

Subscriber software setup

As the sensor publishes MQTT messages there needs to be an MQTT client that subscribes these messages.

There's a list of MQTT libraries on github: https://github.com/mqtt/mqtt.github.io/wiki/libraries

For my local Linux PC I've used the mosquitto-clients package as test setup. The commands mosquitto_sub and mosquitto_pub can be used to play around.

You may want to restart the service:

sudo service mosquitto restart

Pipe it through ts in order to prepend every line with a timestamp:

$ mosquitto_sub -h localhost -p 1883 -t doorbell | ts

Or why not play a sound file remotely?

$ mosquitto_sub -h localhost -p 1883 -t doorbell_connection | xargs -i play -q /usr/share/sounds/KDE-Im-Message-In.ogg
$ mosquitto_sub -h localhost -p 1883 -t doorbell | xargs -i play -q /usr/share/sounds/doorbell.wav

There are better and cooler ways to do things? Let me know! Twitter: @maehw