Figure 2 . Principal circuit diagram of the LAMP device. Max6675: Thermocouple Interface, NODEMCU ESP32: Microcontroller, OLED 1306: Display, LM7805: Voltage Regulator
A microcontroller, ESP32 (Espressif), with Wi-Fi and Bluetooth capability is employed as the controller. The temperature of the aluminum sample holder (Al block, Figure 1 ) is measured using K type thermocouple. The output of the thermocouple is processed by MAX6675 chip and transmitted to microcontroller via SPI interface. A 10 Ohm 15 Watts resistor is placed beneath the sample holder and the heating structure is surrounded by plaster for thermal insulation and integrity. The LM7805 reduces the voltage from 12 V power supply to 5 V for energizing the ESP32 based module. The resistor is energized by a mosfet transistor attached between 12V supply and resistor, IRF540, which is driven microcontroller insulated by an optocoupler. The voltage of the resistance is controlled by Pulse Width Modulation (PWM) generated in the microcontroller. A digital PI controller is utilized in the microcontroller to regulate the temperature of the system. A SSD1306 OLED display is interfaced with the microcontroller over I2C protocol,Figure 1 - Figure 3 . It displays the reference temperature, the actual temperature of the sample holder, duration of the process, and the status of the process, Figure 1 . The device supports Wi-Fi based internet of things (IoT) capabilities. The process parameters (reference temperature, heating temperature slope, duration of the process) and controller parameters may be adjusted. The process variables such as actual temperature and remaining time of the operation may be monitored and stored via web-based interface,Figure 3 .