Raspberry Pi automatic RFID gate opening system with Telegram integration

README.md

Written by: Michele Lizzit <lizzit.it>, 25 Apr 2017
Last update: 25 Apr 2017
Version: 1.0

More informations are available on the project website: https://lizzit.it/cancellino

Cancellino is composed of some active tags and a main unit connected to the gate lock, when the main unit detects the presence of a tag in a set range (configurable from a few cm to 10m), it opens the gate.
Cancellino does not implemet any form of encryption, the tag broadcasts a static key every two seconds, if the key is correct the main unit opens the gate. It was originally designed for applications where the security of the gate is not a concern (in my case the gate is 1m high, and can be easily opened with a piece of plastic).
The main unit is composed of a Raspberry Pi connected to the gate lock and to an nRF24L01+ wireless module.
Each tag is composed of a battery (CR2032), an MCU (Atmega328), and an nRF24L01+ wireless module.

The main unit in place	The gate

• connect the nRF24L01+ module to your RaspberryPI
• enable the SPI interface using raspi-config
• install telegram-cli and enable its daemon
• copy the folder "cancellino" to your RaspberryPI
• configure cancellino by editing "Cancello.java"
• place a script in /home/pi/open_gate_raspi.sh that opens the gate when called (usually a script that sends an high pulse on a GPIO that is connected to the lock via a solid state relay)
• configure the tag by editing Config.h
• upload the tag firmware using Arduino IDE

javac -classpath .:classes:/opt/pi4j/lib/'*' Cancello.java;
sudo java -classpath .:classes:/opt/pi4j/lib/'*' Cancello

To automatically start the software at boot you can create an init file that executes only the last command (there is no need to compile the source code each time).

The tag can be built either by using the PCB or by using a prototype board, the advantage of the PCB version is its small size.

The tag is powered by one CR2032 battery, with one battery the tag can work for about 6 months.
The tag has an ICSP port which can be used to program the MCU (Atmega328P).

A "PCB version" tag	A "PCB version" tag

The MCU is configured to use its internal (8MHz) oscillator in order to minimize the number of electronic components needed for a tag.

Every two seconds the tag broadcasts a string and then puts the nRF24L01+ in "power down" mode, in this mode the nRF24L01+ draws about 100nA.
The module draws 7.0mA while transmitting, but the total time the nRF24L01+ in not in power down mode is about 40ms every 2 seconds so the (theoretical) total power consumption is still very low.
The actual average power consumption I measured is 50µA, which allows about 6 months of continuous operation with a single CR2032.

The nRF24L01+ module on the main unit	The main unit

The receiver is placed on a Raspberry Pi near the gate (I also use the Raspberry Pi as a door phone), when the Raspberry Pi receives an authorized string (which presumably comes from an authorized tag) it opens the gate, plays an audio file and sends a Telegram message containing informations on the tag (who has opened the gate).
In a future software release I plan to implement a feature that notifies the user when the battery is low via Telegram (without requiring a hardware modification).

A prototype of the tag on a perfboard in its 3D-printed case

The tag before soldering the nRF24L01+ module	An AVR programmer connected to a tag via ICSP

A Telegram message from Cancellino