Knock Knock – An Arduino doorbell Telegram notifier

In order to monitor my doorbell – an old mechanical one that is loud but only hearable in one room – I needed a solution. I wanted to use the least amount of third party code. Secondly, because passwords are involved and privacy is important to me, I needed a solution to hook into an existing system that does not need to have my data stored in an IFTTT like website. But the setup and maintenance effort should be minimal. I wanted to have a local, anonymized solution. It also had to be non intrusive as I did not want to open the doorbell or hook into it physically.

This contraption is positioned close to a doorbell and will send a Telegram message once the doorbell rings.

The device is an external addition thus does not interfere with the doorbell circuit making this an easy add on for any situation where the doorbell hardware must not be altered. It is also a good beginners Arduino electronics project as the device is encapsulated in a box that only works with low voltages. Being battery powered it can be activated on demand. To make the most out of the 1400 mAh battery the device goes into deep sleep after one hour and can be easily reactivated via the push button.

Hardware

• D1 mini NodeMcu
• Battery shield
• Lithium polymer battery
• Sound sensor
• Rocker switch
• Push button
• USB panel mount cable
• Junction box

Wiring

Have a look at the wiring diagram first.

1. Strategically mount the rocker switch and the push button in the junction box. Use a cutter to cut openings in the box and pressfit both devices.
2. Strategically route the USB panel mount cable to the surface of the junction box (used to charge the system without opening the box). The linked model is secured with screws.
3. Strategically mount the battery in the junction box (VHB tape works well).
4. Desolder the female JST connector on the battery shield and solder extension cables between the female JST connector leads and the battery shield terminals. This is a good point to check polarity of the JST connectors and the battery: some batteries have the JST connector soldered on the other way!
5. Wire the rocker switch in between the positive lead going from the female JST connector to the positive terminal of the battery shield (ensure enough wire for routing).
6. Wire the push button in between RST and GND of the microcontroller (ensure enough wire for routing).
7. Strategically wire the sound sensor to A0, 3V3 and GND of the microcontroller (ensure enough wire for routing).
8. Drill small holes to the back of the junction box and hot glue the sound sensor to that position with the microphone facing the backside of the box.
9. Mount the battery shield on the D1 mini NodeMcu.
10. Connect the USB panel mount cable to the battery shield.
11. Connect the battery to the female JST connector.
12. Tidy up all cables and ensure correct spacing when closing the box.

You're done setting up the hardware.

Software

Telegram setup

The setup follows these instructions. For simplicity I tried to compress it even more in the following step by step list:

1. Create a Telegram bot using @botfather (FAQ).

   • Username: @<NAME>Bot
   • Disable Allow Groups?
   • Turn on Group Privacy

   The bot Token will be available once the bot is created. Write it down, you'll need it in a later step.

2. Create a private group.

   • Group name: MyPrivateGroup
   • Group Type: private

   Warning: Do not edit special permissions for users as this will convert the group into a supergroup which does not work with this code.

3. Temporarily enable Allow Groups? on the bot.

4. Add the bot to the group.

5. Immediately deactivate Allow Groups? on the bot after adding it to the group.

6. Post a test message into the group via the app or the browser (required to get the next step running). Start message with / in order for the bot to be able to read it (Group Privacy is turned on by default).

7. Retrieve group chat_id by visiting https://api.telegram.org/bot<BOT_TOKEN>/getUpdates in the browser.

8. Let the bot send a test message via visiting https://api.telegram.org/bot<BOT_TOKEN>/sendMessage?chat_id=<GROUP_CHAT_ID>&text=Test in the browser.
   The message should appear in the group chat.

You're done setting up the Telegram infrastructure.

Setup credentials

1. Either rename passwords_template.h to passwords.h or copy its content to a new file named passwords.h in the same folder.
2. Enter your WiFi and Telegram credentials in password.h.

Adjust settings

The system can be fine tuned according to your needs by adjusting the properties in settings.h.

DEBUG

If true prints verbose debug statements via serial connection. Useful for finding issues with e.g. the WiFi connection.

Default false.

NOTIFY_UPCOMING_DEEP_SLEEP

If true sends a Telegram message after RUNTIME_BEFORE_UPCOMING_DEEP_SLEEP_NOTIFICATION_IN_MILLISECONDS announcing the upcoming deep sleep in RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS.

Default true.

NOTIFY_DEEP_SLEEP

If true sends a Telegram message after RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS announcing the immediate deep sleep.

Default true.

SILENTLY_NOTIFY_PROJECT_STARTUP

If true sends the PROJECT_STARTUP_MESSAGE silently. Users will receive a notification with no sound.

Default true.

SILENTLY_NOTIFY_DOORBELL_RINGING

If true sends the DOORBELL_RINGING_MESSAGE silently. Users will receive a notification with no sound.

Default false.

SILENTLY_NOTIFY_UPCOMING_DEEP_SLEEP

If true sends the UPCOMING_DEEP_SLEEP_MESSAGE silently. Users will receive a notification with no sound.

Default false.

SILENTLY_NOTIFY_DEEP_SLEEP

If true sends the DEEP_SLEEP_MESSAGE silently. Users will receive a notification with no sound.

Default false.

RUNTIME_BEFORE_UPCOMING_DEEP_SLEEP_NOTIFICATION_IN_MILLISECONDS

The system is going to announce deep sleep after this amount of time. It will remain functional until RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS is reached. Must be smaller than RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS.

Default 55 minutes.

RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS

The system will go to deep sleep after this time.

Default 1 hour.

NOTIFICATION_LOCK_IN_MILLISECONDS

The system will not send a Telegram message but raise the notification importance level during this lock period. This is so that we stay within the api limits.

Default 1 minute.

NOTIFICATION_RETRIES

Number of attempts to connect to the Telegram server.

Default 3.

SAMPLE_WINDOW_WIDTH_IN_MILLISECONDS

50 ms being 20 Hz.

Default 50.

SOUND_THRESHOLD

If this value is exceeded we assume that the doorbell rings. You might want to test different settings while performing typical sounds in the area you setup this device such as talking loudly or letting a phone ring.

Default 973.

PROJECT_STARTUP_MESSAGE

The message being sent via the Telegram bot when the project is ready.

Default 👂.

DOORBELL_RINGING_MESSAGE

The message being sent via the Telegram bot when the doorbell rings.

Default Knock Knock.

UPCOMING_DEEP_SLEEP_MESSAGE

The message being sent via the Telegram bot notifying that deep sleep starts in RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS - RUNTIME_BEFORE_UPCOMING_DEEP_SLEEP_NOTIFICATION_IN_MILLISECONDS.

Default 😴.

DEEP_SLEEP_MESSAGE

The message being sent via the Telegram bot when the project is going into deep sleep after RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS.

Default 💤.

Flashing the code

1. Download and install the latest release of Arduino IDE.
2. Download the latest release of knock-knock-arduino-doorbell-telegram-notifier.
3. Open Arduino/knock_knock/knock_knock.ino.
4. In the Tools menu select the board LOLIN(WEMOS) D1 R2 & mini for flashing. There is a tutorial on how to install ESP8266 boards in Arduino IDE.
5. Set Upload Speed: 921600 and CPU Frequency: 80 MHz.
6. Connect to the board via USB (not to the battery shield USB that is routed to the outside of the enclosure!).
7. Choose the correct USB Port for uploading.
8. Hit Upload in the Arduino IDE and wait for the process to successfully finish.
9. Unplug the USB cable and close the box making sure that all cables are spaced correctly.

Anonymization

The bot (@<NAME>Bot) can be found by any Telegram user. It exposes no methods to the public so there is no interaction with other users. By using the bot Token we can send messages to certain channels in the name of the bot. Again, this data will never be shared with other users.

To anonymize the bot output even further – and increase the cuteness factor – we use emojis.

System startup

👂 emoji.

Doorbell detected

Knock Knock appended by 0-3 exclamation marks (aka notification importance level).

1. Knock Knock – Doorbell rang once
2. Knock Knock! – Doorbell rang once, subsequently twice within the last minute
3. Knock Knock!! – Doorbell rang once, subsequently three times within the last minute
4. Knock Knock!!! – Doorbell rang once, subsequently four times within the last minute

System preparing for deep sleep

😴 emoji.

System about to enable deep sleep

💤 emoji.

Program flow

1. Activate rocker switch.
2. System boots and broadcasts readiness via Telegram.
3. Code runs.
   1. It reports a ringing doorbell via Telegram.
   2. It reports the upcoming shutdown after RUNTIME_BEFORE_UPCOMING_DEEP_SLEEP_NOTIFICATION_IN_MILLISECONDS of runtime via Telegram.
   3. It reports going to deep sleep after RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS of runtime via Telegram.
      1. It goes into deep sleep after RUNTIME_BEFORE_DEEP_SLEEP_IN_MILLISECONDS of runtime.
4. It can be woken up from deep sleep via the push button (code starts again at #2).
5. The power is cut via deactivation of the rocker switch.

Acknowledgement

Thanks Alex Sarafian for providing great instructions on how to Creating a private Telegram chatbot .

Thanks zenmanenergy for the URL encoding sketch.

And also a great thanks to all people that posted and discussed on various webpages about coding, esp8266 and so on. Wouldn't have made it without you.