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 .