Want to remotely monitor visitors at your door? Why by an off-the-shelf door monitoring solution when building your own is more rewarding? This project features a Raspberry Pi, a Raspberry Pi camera, and an RPi GSM HAT board designed in 2016 by Elektor.

Operation

When a visitor rings the doorbell, a photo of them is immediately taken and sent to a smartphone, allowing you to see who is at the door. You can then call the door system; the built-in GSM module will automatically answer the call. After a brief ring signal, you can speak directly with your visitor using the integrated microphone and speaker. Additionally, you can send an SMS with the correct password to remotely activate an electric door opener. For added security, the system verifies the sender’s phone number to ensure the command comes from your smartphone.
 
Door spy schematic
The major parts in this circuit are the M95 GSM module and the SIM cardholder. Click for PDF

The Schematic and PCB

At the heart of the door monitoring circuit, there is an M95 GSM-module MOD1 with antenna and SIM-card holder SIM1. The resistors R15 through R17, the diode array D7 and the capacitors C19 through C22 serve as noise suppression and ESD protection for the SIM-card interface.

  "The same is true for capacitors C6 through C17 and D3 through D6 for the microphone input and the audio amplifier output of the M95 respectively," Luc Lemmens noted. "The M95 is connected to the Raspberry Pi (K5) via its USART, all communications are done using AT commands. Voltage divider R6/R7 adapts the TxD signal to the 3.3 V rated digital input level of the RPi."

The board fits on top of the Raspberry Pi. The printed circuit board for the door spy is designed as an RPi-HAT and contains mainly SMDs.
 
Door spy pcb
The PCB is designed as an RPi-HAT and contains mainly SMDs.

Door Monitoring Project

The article, “Door Spy Using Raspberry Pi,” appeared in Elektor November/December 2016. You can read the article free during the two weeks following the publication of this news item. If you begin a project of your own, share your progress on the Elektor Labs platform!
Editor's Note: This article originally appeared in a 2016 edition of ElektorMag. Given the project’s age, some components, PCBs, products, or links may no longer be available. However, we believe the content remains a valuable resource and hope it inspires you to start new electronics projects at your workbench.

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