Build Instructions

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• 1

  Tools and Materials

  The following tools and materials were used in this project:

  Tools and materials:

  • 3D printer (link / link / link). It was used for printing the case where the electronics are encloused.

  • PLA filament (link / link / link) of any color you want.

  • Solder iron and wire. Some of the components (ESP32 Firebeetle and HX711, for instance) doesn't come with soldered terminals. I needed to solder some wires or pins in order to connect those devices.
  • Shrinking tube. l also had to solder the wires of each load cell. A piece of shrinking tube might be used for a better isolation of the conductors.
  • Screwdriver. The structure is mounted using some screws. A set of screwdrivers was used.
  • M2x6mm Bolts. They were used for mounting the electronics inside the case.
  • FireBeetle ESP32 dev board. It's really easy to use and program using Arduino IDE. It has built-in Wi-Fi module, so you can use it in a variaty of projects. You can also use other ESP8266 based bords (link / link / link) if you wish.

  • HX711 module (link / link / link). This works as a load cell amplifier. Four strain gauge load cells are connected to this module, and it communicates on a serial communication with the microcontroller.

  • 50kg load cell (x4); (link / link / link). They are used to measure the weight. Four of them were used for a maximum weight of 200kg.

  • Magnetic door sensor (link / link / link). It consists in a magnectic switch, which was used to detect that the litter box is opened.

  • Micro USB cable;
  • 6 female-female jumper wires;
  • Cat litter box.

  The links described above are only a suggestion of where you can find the items used in this tutorial (and support my future hacks). Feel free to search for them elsewhere and buy at your favourite store.

  I used a FireBeetle ESP32 dev board, which was kindly supplied by DFRobot.

  Did you know you can buy a Creality Ender 3 3Dprinter for only $168.99? Get yours! https://rebrand.ly/3Dprinter-BG

• 2

  Setup FireBeetle ESP32 on Arduino IDE

  For this project I used Arduino IDE for programming my ESP32 module. It's the easiest way if you've already used an Arduino before, and you won't need to learn a new programming language, like Python or Lua for instance.

  If you've never done this before, first you'll have to add ESP32 board support to the Arduino software.

  1. Download and install Arduino IDE latest version

  You can find the latest version for Windows, Linux or MAC OSX on Arduino's website: https://www.arduino.cc/en/main/software

  Download it for free, install it on your computer and launch it.

  2. Adding ESP32 board

  Arduino IDE already comes with support to a lot of different boards: Arduino Nano, Mine, Uno, Mega, Yún, etc. Unfortunatly ESP32 isn't by default among those suported development boards. So in order to upload your codes to a ESP32 base board, you'll have to add its properties to Arduino's software first.

  • Navigate to File > Preferences;
  • Add the following URL to Additional Boards Manager textbox (the one on the bottom of the Preferences window):

  https://git.oschina.net/dfrobot/FireBeetle-ESP32/raw/master/package_esp32_index.json

  • If the text box wasn't blank, it means had already add other boards before on Arduino IDE before. Add a comma at the end of the previous URL and the one above.
  • Hit "Ok" button and close the Preferences Window.
  • Navigate for Tools > Board > Boards Manager for adding your ESP32 board.
  • Type "FireBeetle-ESP32" on the search text box, select "FireBeetle-ESP32 Mainboard by DFRobot DFRDuino" and install it.

  Now your Arduino IDE will be ready to work with ESP32 FireBeetle board.

  Plug the microUSB cable on the ESP32 and on your computer. It will automatically install Windows communication driver. If it fails to install the driver, download the following file and manually install the driver for the newly connected device.

  https://git.oschina.net/dfrobot/FireBeetle-ESP32/raw/master/FireBeetle-ESP32.inf

  If you wish to use an alternative ESP32 based board, add the appropriate board.

  3. Adding the libraries

  The following libraries will be used for our Arduino code. Download the following libraries:

  • Thingspeak library: https://github.com/mathworks/thingspeak-arduino
  • HX711 library: https://github.com/bogde/HX711

  Navigate to Sketch-> Include Library -> Manage Libraries... on your Arduino IDE and add the libraries above.

  ............

  Now that your dev environment is ready, let's move on to the next step!

• 3

  Wiring Up - HX711, Load Cells, Reed Switch and ESP32

  This project used the following electronic components:

  • ESP32 Firebeetle development board: This board has an Expressif microcontroller and is the component responsible for reading variables, handling and sending data to the cloud using a WiFi connection. It is in this device that the project code runs.

  • Load Sensors: component responsible for measuring the force, converting the pressure applied on the device into an electrical signal.
  • Amplifier HX711: circuit responsible for the amplification of the electric signal generated by the charge cells and digital analogue conversion of sina. The signal generated by the load cells has a very restricted amplitude (signal in mV). This circuit amplifies this signal and performs the conversion of the analog signal to digital, delivering the converted signal to the microcontroller.

  • Door sensor switch: consists of a switch that is normally closed in the absence of a magnetic field. When applied a magnetic field in its proximity, the switch closes an internal contact, allowing the conduction of electric current. In this project, a switch of this type was used to identify whether or not the top of the litter box was opened. A magnet has been attached to the top cover, while the switch is attached to the controlled and fixed on the bottom of the box. When that cover is closed, the magnet and key will be aligned and close together, keeping the switch closed. When the two parts are separated, the magnet will move away from the switch and the circuit will open.

  Each device was connected according to the schematics.

  HX711 - input:

  • Upper left load cell signal (red wire) => HX711 E- pin
  • Lower left load cell signal (red wire) => HX711 A+ pin
  • Upper right load cell signal (red wire) => HX711 A- pin
  • Lower right load cell signal (red wire) => HX711 E+ pin

  HX711- output:

  • HX711 Vcc pin => ESP32 3.3V pin
  • HX711 GND pin => ESP32 GND pin
  • HX711 SCK pin => ESP32 GPIO 2 (pin D9)
  • HX711 DT pin => ESP32 GPIO 5 (pin D8)

  Door sensor:

  • Reed switch (terminal 1) => ESP32 GND pin
  • Reed switch (terminal 2) => ESP32 GPIO 25 (pin D2)

  When everything is wired up, plug a USB cabe on the ESP32 and get ready for uploading the code.

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