ESP32 Dual Machine Activity Notifier

This project transforms an ESP32 into a smart monitoring device. It uses two light sensors to track the activity of machines like a washer and dryer, sending notifications to your phone or desktop when a cycle starts and finishes. A local OLED display provides real-time status at a glance.

Features

Dual Light Sensing: Monitors two separate devices using two BH1750 light sensors.
Real-time Status Display: Shows current sensor data and machine status on a 128x64 SSD1306 OLED display.
Push Notifications: Sends instant start and stop notifications via a self-hostable ntfy.sh topic.
WiFi Connectivity: Connects to your local WiFi network.
Non-Blocking Logic: Uses millis() for timing, ensuring the device remains responsive.

Hardware Requirements

ESP32 development board
2x BH1750 light sensor modules
SSD1306 128x64 OLED display (I2C)
Breadboard and jumper wires

Wiring and Connections

All components use the I2C communication protocol, which conveniently allows them to share the same data (SDA) and clock (SCL) lines.

I2C Address Configuration

To use two BH1750 sensors on the same I2C bus, they must have different addresses. This is a critical step.

Sensor 1 (Address 0x23): Connect the ADDR pin to GND. This sets the address to the default 0x23.
Sensor 2 (Address 0x5C): Connect the ADDR pin to 3.3V. This changes its I2C address to 0x5C.

Pinout Table

Component	Pin on ESP32	Notes
I2C SCL (OLED, Sensors)	GPIO 22	Shared I2C Clock Line
I2C SDA (OLED, Sensors)	GPIO 21	Shared I2C Data Line

Wiring Diagram

+-----------------+           +-----------------+      +-----------------+
| ESP32 Dev Board |           | BH1750 Sensors  |      |   OLED Display  |
+-----------------+           +-----------------+      +-----------------+
| 3.3V            |---------->| VCC             |----->| VCC             |
| GND             |---------->| GND             |----->| GND             | 
|                 |           |                 |      |                 |
| GPIO 22 (SCL)   |---------->| SCL             |----->| SCL             |
| GPIO 21 (SDA)   |---------->| SDA             |----->| SDA             |
+-----------------+           +-----------------+      +-----------------+

Note: For Sensor 1, connect the ADDR pin to GND (or leave floating if default is low). For Sensor 2, connect the ADDR pin to 3.3V to change its I2C address to 0x5C.

Setup & Usage

Install Libraries:
- Open the Arduino IDE and go to Sketch > Include Library > Manage Libraries....
- Install the following libraries:
  - Adafruit SSD1306 by Adafruit
  - Adafruit GFX Library by Adafruit
  - BH1750 by Christopher Laws
Configure the Code:
- Copy secrets_template.h to a new file named secrets.h in the same directory.
- Open secrets.h and populate SECRET_WIFI_SSID, SECRET_WIFI_PASSWORD, and SECRET_NTFY_TOPIC with your WiFi credentials and desired ntfy.sh topic.
- The secrets.h file is ignored by git to keep your credentials safe.
Upload the Code:
- Connect your ESP32 board to your computer.
- Select the correct board and port in the Arduino IDE.
- Click the upload button.
Deploy the Device:
- Make the connections according to the wiring diagram, which is quite simple. All 3 peripheral devices communicate over I2C, which lets them share the same 4 wires.
- Place Sensor 1 & 2 on the respective machines such that they only detect light when the device is running. This is specific to each monitored device. The "Start/Stop" button LED is a great candidate for this.
- Make sure to block off any ambient light that might interfere with whatever you're monitoring (e.g. by using a tape).
- Tip: wire the sensors using connectors, so that you can later disconnect the main unit (e.g. for a firmware update) without having to remove the sensors from the monitored machines.
- Tip: use a power socket with a switch to enable/disable the monitoring as needed

Code Explanation

The code is structured as follows:

- It continuously reads the values from both light sensors.
- It implements a non-blocking logic using `millis()` to check if the sensors have been in a certain state (light level high) for a continuous period.
- It updates the overall device states (`isDevice1Active`, `isDevice2Active`) based on the individual sensor states.
- If the device state changes, it calls `sendNotification()`.
- It calls `updateDisplay()` to show the latest data.

sendNotification(): Sends a POST request to the configured ntfy.sh topic with a message.
updateDisplay(): Manages the OLED display. It clears the screen and prints the current status of the sensors and the device. It also implements a scrolling feature to cycle through the displayed information every 2 seconds.

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