Device Function

1. As soon as the device starts it checks for configured wifi credentials and connects to wifi network.
2. Then it starts reading the weight scale and waits for any weight adding to the scale.
3. Once a weight add to the scale, it immediately increments the counter and displays in the screen. Both add and remove will increment and decrement the counter acurately.
4. Mean while, if user press the button it will send the current item count and send it to the server. The respose from the server will be the cashier No. and will be displayed to the user.
5. When the cashier No. displays the Blue LED will also turn ON.
6. If user switch the button again, it will again show the current item count and the Blue LED turn OFF.

Device Schemetic

Power Supply

1. There are 2 18650 Lithium 3.7v Batteries.
2. DC-DC Regulator and 7805 5v Regulator converts the Voltage to stable 5v.
3. The red 5v wire from regulator connects to NodeMCU Pin VV and Black wire connects to any GND pin. This powers the NodeMCU Module. The Red LED just indicates the power supply.
4. NodeMCU outputs 3.3v for other pins.

OLED Display

More Info - 0.96 inch OLED Display with Arduino IDE

1. OLED SDA pin connects to NodeMCU D2 pin.
2. OLED SCL pin connects to NodeMCU D1 pin.
3. Red 3.3v and Black GND.

We’re using I2C communication protocol. The most suitable pins for I2C communication in the NodeMCU are GPIO 5 (SCL) and GPIO 4 (SDA).

Weight Sensor Digital Scale

More Info - NodeMCU with Load Cell and HX711 Amplifier (Digital Scale)

1. HX711 DT pin connects to NodeMCU D6 pin.
2. HX711 SCK pin connects to NodeMCU D7 pin.
3. Red 3.3v and Black GND.

Switch and Blue LED

1. Switch connects to NodeMCU D5 and GND pins.
2. Blue LED connects to NodeMCU D8 and GND pins.