IOT Intercom

This repo contains software and schematics that I used to make a 'smart' intercom. It is a high-tech replacement of my Siedle intercom using old hardware. It's basically some libraries cobbled together which might inspire you if you are trying to do the same.

Introduction

A couple of year ago I stumbled upon an old German industrial phone. This thing was manufactured by Funke & Huster, weights 17 kilograms and is supposed to be explosion proof. I live in an apartment building with a Siedle intercom system and thought this would make a nice replacement for the ugly plastic Siedle doorphone. Of course replacing the hardware provided a perfect opportunity to integrate the intercom into my Domotica system.

Features

• Uses the original ringer for physical notifications
• The rotary input can be used to start an action or toggle settings
• Auto-unlock feature automatically unlocks the door when the doorbell button is pressed.
• Mute function for when you do not want to be disturbed..
• Has Wifi and can talk MQTT to your domotica software so you can:
  • Receive a push notification when someone rings your bell
  • Use voice command to unlock the door
  • Automatically pause Kodi when doorbell is pressed
  • Remotely unlock the door.

Hardware used

• NodeMCU v3
• Siedle HTC 711-01 (only need the print)
• 2x Boost Buck DC adjustable step up down Converter XL6009
• Funke & Huster Bunker phone
• L298N H Bridge Motor Driver Board
• 4N25 OctoCoupler
• Zenerdiode 1N4746
• Some resistors and capacitors and transistors
• sip-1a05 reed relay.

Software

The software acts a state machine to control the hardware. The software makes sure to detect when the doorbell is pressed, capture input from the rotary dail or ring the bell etc. Homie-esp8266 is used to make the intercom smart and let it communicate via MQTT.

I am using PlarformIO for development. In order to use the Homie-esp8266 library you need the platformio.ini file accordingly;

[env:nodemcuv2]
platform = espressif8266
board = nodemcuv2
framework = arduino
build_flags = -D PIO_FRAMEWORK_ARDUINO_LWIP2_LOW_MEMORY
lib_deps = git+https://github.com/homieiot/homie-esp8266.git#develop

Control via MQTT

The hardware can be controlled via MQTT. It has four functional nodes which can be configured and controlled via MQTT or serial.

• Latch node, for everything related to unlocking the door
• Bell node, for everything related to controlling the bell
• Rotary node, for handling rotary input
• System node, for resetting or configuring the system

A complete overview of the nodes and their properties can be found in the MQTT section. Not all properties are settable. For the one that are you can use the MQTT topic + /set to control it.

Some examples:

Action	Topic	Value
Ring the bell	/home/deviceid/bell/ring-bell/set	true
Unlock the door	/home/deviceid/latch/unlock/set	true
Set bell to ring 4 times	/home/deviceid/bell/bell-repeats/set	4
Reset via internal command	/home/deviceid/system/command-input/set	951

Internal/serial commands

Internally the software works with three-digit commands which can be useful for debugging. You can set them via MQTT (/home/deviceid/system/command-input/set/) or via serial if debug is enabled. You can find the CMD ID's in the MQTT sections. The CMD's + action makes a valid command. Actions: 0, to turn off, 1 to enable, 2 to toggle and 3 for status.

Below are some examples. Note that some things can be switched like actions. They can only be enabled or toggled.
You can find all the CMD ID's in the MQTT section.

Action / Switch	CMD ID	Disable	Enable	Toggle
auto-unlock	160	160	161	162
short-ring-bell	250	n/a	251	252
bell-muted	270	n/a	271	272

Note that nothing is stored in EPROM.

Hardware

Interfacing with Siedle 1+n

My apartment building has a Siedle 1+n system which uses a two wire system. One common wire and an individual signal wire. Unfortunately the actual intercom system which lets you talk to the person at the door doesn't work so I cannot use that.

To interface the new old phone with the intercom system I am using the PCB of the Siedle doorphone. Some wiring is needed

1. The print has a reed relay in the middle to detect whether the horn (which has a magnet) is on the receiver. This will control the output volume of the speaker. Don't forget to connect it permanently or wire it to a switch.
2. The door unlock button is needed to send the unlock signal. See Unlocking the door
3. We need to connect to the intercom bus. See Detecting doorbell events

Detecting doorbell events

The most important feature of the intercom is to let me know if somebody is ringing my apartment. The voltage on the 2-wire Siedle system (Pin 7 and 1) is ~14,2 volt when idle but rises briefly to 22,9v when the doorbell is pressed.

A circuit with a Zener diode and an Octocoupler is used to catch this signal. The 1N4746 has a Zener voltage of 18v and is connected in reverse bias to PIN 7 of the Siedle. When someone pushes the doorbell the voltage rises to 22,9v and exceeds the Zener voltage causing an Avalanche Breakdown to occur resulting in (22,9 - 18) ~4,9 volt to be let through.

This in turn drives the input source of the Optocoupler.

Driving the telephone bell

Like most landline phones my replacement phone has a polarised bell which is normally powered by applying a 50 to 100 volt AC at 20 Hertz. This is not a very convenient voltage to work with so I am using an H-Bridge to mimic this. A L298N H-bridge board reverse the polarity on the magnet of the bell every 50ms. I am driving it with ~30v provided by the XL6009 converter.

Unlocking the door

To open the central door of my apartment building (‘buzz someone in’) a small circuit is used to drive a sip-1a05 reed relay. This relays shortens the door release contacts on the HTS-711 print.

The relay can be activated by software but it is more convenient to have a physical button. I am using a handle on the bunkerphone to buzz someone in. In my case the switch connected to this handle triggered some unintended interrupts with fluctuations on the power grid so I added some pull-up resistors and a capacitor.

Input from the rotary dialer

The phone has a nice rotary dial which I can use to interface. I use it to enable the auto-unlock feature for a period of time or to tell my Domotica system (Homey) to switch of all devices. THe rotary dail has two output and are connected like this:

MQTT Configuration

The system uses the Homie convention for MQTT communications. You can find the complete configuration here. Most features work but not all of them.

Device attributes | homie/

Device ID	$homie	$name	$state	$nodes
iot-intercom	3.0.1	IOT Intercom	ready	latch,bell,rotary,system

Device nodes | homie/device-id/

Node	CMD ID	$name	$type	$properties
latch	100	Central Entrance Door Latch	Pulse open	unlock,auto_unlock,buzzer-button,last-unlock, unlocks
bell	200	Intercom bell	AC Bell	doorbell-pressed,doorbell-pressed-time,ring-bell,short-ring-bell,bell-repeats,bell-offtime-ms,bekl-on-time-ms
rotary	300	Rotary dialer input	Old style	rotary-input,last-rotary-input
system	900	System settings	command-input,force-mqtt-update, reset,factory reset

Latch node properties | homie/device-id/latch

Property	CMD ID	$name	$datatype	$format	$settable	$retained
unlock	140	Unlock door	Boolean		Yes	No
auto-unlock	160	Auto unlock door	Boolean	Yes	No
auto-unlock-min	170	Remaining auto unlock minutes	Integer	0:360	Yes	Yes
unlock-button	110	Buzzer button pressed	Boolean		No	No
last-unlock		Last unlock time	String	date time	No	Yes
unlocks		Number of unlocks	Integer	#	No

Bell node properties | homie/device-id/bell

Property	CMD ID	$name	$datatype	$format	$settable	$retained
doorbell-pressed	210	Doorbell is pressed	Boolean		No	No
doorbell-pressed-time	290	Last time doorbell was pressed	String	date time	No	Yes
ring-bell	240	Ring the bell	Boolean		Yes	No
short-ring-bell	250	Short ring the bell	Boolean		Yes	No
bell-muted	270	Mute the bell	Boolean		Yes	Yes
bell-repeats		Number of times the bell should ring	Integer	1:10	Yes	Yes
bell-off-time-ms		Bell pause duration	Integer	10:10000	Yes	Yes
bell-on-time-ms		Bell on duration	Integer	10:10000	Yes	Yes

Rotary node properties | homie/device-id/rotary

Property	CMD ID	$name	$datatype	$format	$settable	$retained
rotary-input	310	Rotary dialer input	Integer	0:9	No	No
rotary-input-time	390	Last rotary input time	String		No	Yes

System node properties | homie/device-id/SYSTEM

Property	CMD ID	$name	$datatype	$format	$settable	$retained
command-input	910	Command Input	Integer	100-999	Yes	No
force-mqtt-update	940	Force MQTT update		Boolean	Yes	No
reset	950	Force reset	Boolan		Yes	No
set-debug	960	Debug enabled	Boolean		Yes	Yes
factory-reset	999	Factory reset	String		Yes	No