There are some pretty cool smart doorbells out there, but they are expensive and the basic components of a wireless button, camera and a small computer are cheap! In fact the most expensive component in this project is the camera module, which is still a bargain at sub 20 USD.
An overview of the system is shown in Figure 1. When someone pushes the doorbell button, the button module transmits a 433 MHz RF signal to a receiver (not show) which sounds a chime. However, the RF signal can be freely intercepted (not ideal for security but pretty convenient), and here an RF module attached to a Raspberry Pi is used to intercept the RF signal. On receiving the signal, the Pi takes an image using the camera. This image can then be sent as a mobile notification, for example using the Telegram app. In this project, I actually send the image to my home automation system, Home-assistant.
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Make a robot friend with Adafruit’s CRICKIT – A Creative Robotics & Interactive Construction Kit. It’s an add-on to our popular Circuit Playground Express, FEATHER and other platforms to make and program robots with CircuitPython, MakeCode, and Arduino. Start controlling motors, servos, solenoids. You also get signal pins, capacitive touch sensors, a NeoPixel driver and amplified speaker output. It complements & extends your boards so you can still use all the goodies on the microcontroller, now you have a robotics playground as well.