Auta Building Intercom and Entry System
Background
In the apartment I'm currently living in, the building intercom and entry system unit is installed outside the living room door, plus I usually play music or sleep in the bedroom further inside, it's rather difficult to hear the doorbell, thus I frequently miss the deliveryman. So I decided to integrate it into my Home Assistant, then another benefit is that I don't need to take my keys anymore when go out.
After removing the case, the sticker on the PCB shows that the model number is "auta 700105"
Hacking
According to the technical manual found on the manufacturer's website, the four wires that came from outside the apartment to terminal CON1
are, from left to right, GND (black), +24 VDC power (brown), microphone (blue), speaker and data (gray). CON2
connects the handset via an RJ11 connector.
I took out the PCB and started to reverse engineer the circuit.
The ICs:
U1
is a "78L05A" voltage regulator, which provides +5 V to other components-
U2
is a "PIC16F870-I/SO" MCU, which implements the main functions -
U3
is a "ULN2003A" Darlington transistor array, which lets the MCU to drive peripheral circuits- Channel 1: input is the MCU's PIN27
RB6
, output is the handset speaker amplifier circuit - Channel 2: input is the MCU's PIN26
RB5
, output is the relayRY1
- Channel 3-7: input is the MCU's PIN25
RB4
, output is the "Auxiliary bell (24 Vdc output, in call)" terminals of CON1
- Channel 1: input is the MCU's PIN27
U4
is a "LM393" voltage comparator- Comparator 1 is not used
- Noninverting input 2: +12 V
- Inverting input 2: the "Speaker and Data" terminals of CON1
- Output 2: PIN23 of the MCU
U5
is a "PC357NJ0000F" optocoupler, input is the "Ding-Dong function (tension free button)" terminals of CON1, which pulls down the MCU's PIN22RB1
when they are shorted
MCU pin functions
- 1
MCLR
: reset - 2
RA0
: input of the bell melody select buttonPB1
(low level trigger) - 3
RA1
: output of the red LED - 4
RA2
: output of the green LED - 5
RA3
: input of the building door unlock button (low level trigger) - 6
RA4
: input of the AUX1 button (low level trigger) - 7
RA5
: output of unlock signal? - 8
Vss
: GND - 9
OSC1
, 10OSC2
: inputs of the crystal oscillatorX1
- 11
RC0
- 14RC3
: inputs of the 5-8 positions of the DIP switchSW1
(low level trigger) - 15
RC4
- 18RC7
: inputs of the 1-4 positions of the DIP switchSW1
(low level trigger) - 19
Vss
: GND - 20
Vdd
: +5 V power input - 21
RB0
: input of the master-slave selection jumperJ1
(high level as master) - 22
RB1
: input of the "Ding-Dong function (tension free button)" through optocouplerU5
's collector pin (low level trigger) - 23
RB2
: input of the doorbell signal? - 24
RB3
: output of the unlock signal? - 25
RB4
: output of the "Auxiliary bell", through the driver ICU3
's channels 3-7 (high level trigger) - 26
RB5
: output of the relay, through the driver ICU3
's channel 2 (low level trigger) - 27
RB6
: output of the doorbell sound to the handset speaker, through the driver IC's channel 1 - 28
RB7
: input of the switchhook for handset (low level while hanging)
We can see that PIN5 RA3
can be used to unlock the building door, and PIN27 RB6
can be used to detect if the doorbell is ringing.
Hardware
The circuit is shown in the following figure, since the PIC uses 5 V TTL but ESP8266 uses 3.3 V, they need a logic level shifter to talk:
Install
As shown in the figure, +5 V (purple), GND (green), MCU PIN5 (white) and PIN27 (blue) are tapped from several contacts that are easy to solder:
Since I already have an ESPHome device (Whole Home Energy Monitoring) lying nearby, I just modified and reused it (the 4-pin DuPont cable is for the PZEM energy monitor):
Connected to the intercom phone with an old USB cable:
Software
Example ESPHome configuration:
esphome:
name: building-intercom
comment: 'Auta building intercom and entry system hack'
esp8266:
board: d1_mini
preferences:
flash_write_interval: 10min
logger:
level: WARN
baud_rate: 115200
wifi:
fast_connect: true
networks:
- ssid: !secret wifi_ssid
bssid: !secret wifi_bssid
password: !secret wifi_password
api:
ota:
password: !secret ota_password
binary_sensor:
# intercom bell sensor
- platform: gpio
pin: 12
id: intercom_ringing
name: 'Building Intercom Ringing'
filters:
- delayed_off: 30s # adjust this to the actual ringing time
icon: mdi:bell-outline
on_press:
- homeassistant.service:
service: script.building_intercom_ringing_notification
output:
# pull down to trigger the unlock button
- platform: gpio
id: intercom_unlock_door_button_output
pin:
number: 14
inverted: true
button:
# expose the unlock button to HASS frontend
- platform: output
id: building_door_unlock_button
name: 'Unlock Building Door'
output: intercom_unlock_door_button_output
duration: 3s
icon: mdi:door
After flashing the firmware, it can be added to HASS:
Then I created a script in HASS to push a notification to my phone when the intercom bell is ringing:
alias: Building Intercom Ringing Notification
mode: restart
icon: mdi:bell-outline
sequence:
- service: notify.mobile_app_phone # target phone
data:
message: 'Building Intercom Ringing'
data:
push:
sound:
name: default
critical: 1
volume: 1
actions:
# a button to unlock the door
- action: UNLOCK_BUILDING_DOOR
title: 'UNLOCK'
destructive: true # show it in red
And an automation is needed to receive the unlock button event from the notification (the following YAML is only for display and the automation should be created using the UI):
alias: Unlock Building Door by Notification Callback
mode: restart
trigger:
- platform: event
event_type: mobile_app_notification_action
event_data:
action: UNLOCK_BUILDING_DOOR
condition: []
action:
- device_id: f13cff1a6a2eb06cbd79e584e91f2e21
domain: button
entity_id: button.unlock_building_door
type: press
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