Know when someone rings your mechanical door-bell, even when you're out of earshot.
This is our door bell:
Inside:
Our office is on the other side of our house, and I frequently don't hear the bell when I'm working from home. However, we really like the bell as it is, so we didn't want to replace it with something like a boring Ring doorbell.
So I needed something that detects motion at the bell-end, and is able to send this wirelessly to another device, which in turn can somehow let me know that things are happening. I settled on a Pi Pico W with a tilt-switch as motion detection as the sender, attached to the doorbell. A Pi Zero acts as the receiver, attached to a regular light in my office.
- A Raspberry Pi Pico W
- Some kind power supply (I used 4xAA rechargeable batteries). Depending on the power supply you need some kind of battery case.
- SW-520D tilt switch.
- Two jumper wires (about 4-5cm) to attach the tilt-switch with.
- (Optional) An on-off switch (I like this type)
Attach the tilt-switch unto the end of the wires. In my case they needed to be a few centimeters long, to provide the tilt-switch with enough range of motion to trigger whenever the bell rings. Attach the wired-up tilt-switch to any of the regular pins and a ground pin. Make sure to set that same pin in the motionsensor.py on line 12. In the code provided it's attached to GP11 (physical pin 15). Make sure the tilt-switch points upwards, otherwise it won't work.
Attach the Pico to the battery unit with some tape or hot glue and popsicle sticks. Make sure that you're able to open the battery compartment to recharge your batteries.
Wire the power supply to the VSYS and a ground pin. I wired the on-off switch on the ground wire in between the battery and the Pico: I only turn it on when I am expecting someone or a delivery.
Front
Back
Side
Attach the sender to any moving part of the bell. Gaffer-tape might do just fine:
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You need a Raspberry Pi, such as the Zero W, but any of the Pi's with Wifi could do in this case. The receiver code is written in Python, but can easily be modified to run in MicroPython. Just make sure that in that case, the MQTT broker is running from some other device. In this project, the broker runs on the same device as the receiver.
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A relays breakout board. Alternatively, follow along in the excellent Udemy course by Dr. Peter Dalmaris on (amongst many other things) how to make your own relays circuit:
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Some power supply. I opted to use an old iPhone charger which from which the USB cable has it's 5V and ground wires connected to jumper wires. These connect to 5V and ground pins on the Zero. This was done because in my case ther was no space to connect the micro-USB connection.
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A case to hold everything in. I used a box from a wrist-watch.
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Male and female power-sockets with some cabling.
Attach the relays to pin 21 on the receiver (or at least to the same pin as is in the mqttclient.py script).
Attach the ground cable of the power sockets to the relays (I opted for the NC channel, so that if my relays somehow failed, the light would still be on). Again, check Dr. Peter Dalmaris' explanation on how to do this properly.
I glued the relays (breakout) board to the lid of the box, with cabling long enough so I can just open the case if I need to:
Finished receiver:
Attach a light or something useful to you to the female power socket of the receiver. It will toggle off-on a few times in response to the MQTT signal.
Through testing I found that I could get the best battery life of the sender using a setup with 4 rechargeable AA batteries. This provides between 50 and 60 hours of battery life.
This is also why I added the external on-off switch to the sender. I want to be able to turn it off when not needed. The downside is that now I have to remember how many cummulative hours it has been on since last charge.
Additionally, the Wifi only connects once motion is detected, and then only stays on for a couple of minutes. This does delay the response between sender and receiver (it is between 5-10 seconds before the receiver starts toggling), but it does increase the battery life.
In the wifi_connect.py you need to fill out your WiFi SSID and password.
Setup the Mosquitto broker. A good explanation on how to set this up on the Pi can be found here. In both the mqtthandler.py (on the sender) and the mqttclient.py (on the receiver) you need to fill out the IP-address of your MQTT broker.
To make sure the receiver always works, even after power failure, it needs to run as a service on the device, and start automatically on boot.
On the receiver, copy the the mqttclient.py script to /usr/bin/mqttclient.py.
Copy the systemd file mqttclient.service to: /etc/systemd/system/mqttclient.service
Reload, start, and enable systemctl and our new service:
sudo systemctl daemon-reloadsudo systemctl enable mqttclient.servicesudo systemctl start mqttclient.service
Your sender will probably crash if the MQTT broker is not yet turned on. Make sure the broker is operational before turning on the sender. Turn the sender off and on if this got mixed up somehow.
Hit the on-switch on the sender. Once the sender detects bell-related-motion, it will establish a WiFi connection (slow LED blinks during connection, rapid blinks once connected). Then it will blink quickly again to indicate motion has been detected, and it will let the receiver know via the MQTT protocol. The WiFi connection stays active for a couple of minutes, then shuts down to conserve battery.
The receiver receives the signal from the MQTT, and will toggle the relays on and off a few times. If a light is attached, this will flicker. Otherwise, attach a light, and watch it flicker. If you prefer a fan, TV, or microwave, that is fine too. I'm not sure about the microwave, please let me know how that worked out.
To me the project is at a good stage: I got the device to a stage where I wanted it to be, and it is quite useful to me.
However, of course there's a lot of room for improvement. Some future ideas might include:
- Improving the battery life of the sender from 50-60 hours to weeks or months
- Reducing the physical footprint of the sender
- Improving the response time of the sender/receiver connection from 5-10 sec to 1-2 sec
- Swapping the receiver Pi Zero for another Pi Pico W
Any ideas and improvements are welcome!
Wherever applicable I noted in the scripts where I got the original code from that I based my work on. Thanks a million to the giants before me!
You are free to use and modify this project to your heart's content.