Home Defender: a smart alarm for our home

HOMEDEFENDER

STORY

We all want our home to be a safe place to take refuge in. One of the greatest fears of all of us is that someone might violate our home, invading our "safe place." It was from this very premise that the idea of creating HomeDefender was born. HomeDefender is a low-energy and also inexpensive IoT-system.

But let's see how it is constructed.

BOARD, SENSOR & ACTUATOR

Board

ESP32 Heltec LoRa32 v2

The Heltec LoRa32 v2 is a development board with 8 MB Flash that uses the EPS32 chip directly. It integrates: - a SemTech SX1276 or SX1278 for LoRaWAN communication and - a SSD1306 0.96-inch 128x64 OLED display connected via I2C.

PIR HC-SR501

The HC-SR501 PIR motion sensor is one of the easiest to connect to an Arduino -or any other microcontroller for that matter- and can also be used as a stand alone motion detector. The HC-SR501 board has 2 variable resistors: looking at the back, with the connections facing upwards and the variable resistors at the bottom, the left resistor is for sensitivity and the right one is for output timing. for the sensitivity goes: Clockwise=>High sensitivity CCW=> low sensitivity (3-7 m). for the Output timing it is CW=>long, CCW=> short (3-300 sec) The right prong of the connector is for Vcc (+5- 20V), the middle one is signal out and the left one is ground. The output is either high (3.3V) or low (0v)

Specification

• Voltage: 5V
• Power Consumption: 65 mA
• TTL output: 3.3V, 0 V
• Trigger methods: L – disable repeat trigger, H enable repeat trigger
• Sensing range: less than 120 degree, within 7 meters
• Temperature: – 15 ~ +70

Buzzer

This module is similar with the Active Buzzer Module, the only difference is that this module only can be driven square wave signal, not DC signal. Here the “source” does not mean power. But rather refers to the shock source (Frequency). In other words, the active internal buzzer with shock source. The passive internal sources without shocks, so if a DC signal can not make it tweet. Must 2K ~ 5K square wave to Drive it.

Specification

• Operating Voltage 3.5V ~ 5.5V
• Maximum Current 30mA / 5VDC
• Minimum Sound Output 85dB @ 10cm
• Resonant Frequency 2500 ±300 Hz
• Operating Temperature -20°C to 45°C

CIRCUIT

Here we can see all the connections between the components and the board.

For be clear, the Pir sensor is connected on PIN_13 and the buzzer on PIN_23.

NETWORK DIAGRAM

As for the network infrastructure, the board is connected via an MQTT bridge to AWS in which all movements detected by the system are recorded.

EVALUATION

As for the evaluation of the system, it was done by recording the consumption of the various components.

From the datasheets of the sensor we have that:

• PIR sensor 65mA
• Buzzer 30 mA

But the buzzer remain active only for 1.5 seconds, and only when a movement was registered, that means that it could be off for all the time.

So to estimate the consumption I have considered only the consumption of the PIR sensor because as the buzzer also the messages and the communication go up only with some detection.

So the consumption of the system is ≈ 65mA to which must be added the consumption of the board, which in our case amounts to about 50mA (this measure is given by the study done in the project PaaT).

So in conclusion the total consumption is ≈ 115mA.