1. Design

1. See Figure 1 for details of the development drawing.
2. Cut a 3-mm thick acrylic board to 210 mm in width x 60 mm in height x 104 mm in depth, bond with acrylic adhesive and assemble the case.
3. Install as many as 30 optical cells of 12.5 x 12.5 mm.
4. Attach switches and lamps for starting and stopping and a variable dial for the drying time setting on the front face of the casing.
5. See Figure 2 for an external view and component configuration.
6. Use acrylic and nylon for the casing and net, respectively. Fix the net to the frame and attach it to the upper part of the case.
7. Use acrylic for the lattice of the optical-cell installation. Attach it to the top of the net.
8. Mount the blowers to the back of the case.
9. Use translucent acrylic for a waterdrop prevention partition.

2. Hardware Design Outline

1. See Figure 3 for details of the circuit diagram.
2. Step down from 12 V to 5 V by a three-terminal regulator for operating the microcomputer.
3. Activate the blowers via an NPN transistor (25 V, 500 mA).
   Note: Because the output pin of the microcomputer is 5 V.
4. Control the rotation speed of the blowers by the pulse width modulation (PWM) operation of the output pin.
   Note: The blower is being driven, the number of revolutions is controlled, and the strength is periodically changed.
5. Connect the start push switch to the digital input pin.
6. Connect the blowers’ operation time setting volume to the analog input pin to change the voltage according to the rotational position.
7. Connect the organic light-emitting diode (OLED) for the operation time display to the two digital output pins with an inter-integrated circuit (I2C).
8. Connect the LED that lights up during the operation to the digital output pin.

3. Software Design Outline

1. Use a microcomputer to control the blowers.
   Note: The development environment was constructed using Arduino, which is one of the development environments called open-source hardware, and all circuits and software are open to the public.
2. Outline of the operation
   1. Press the start switch.
   2. Read the state of the button specified by the select button on the front and activate the blower according to that state.
   3. Read the drying time set by the variable resistor on the front as a voltage signal and start counting down the timer.
   4. Turn the LED lights up and display the remaining time on the OLED.
3. Detailed explanation
   1. Read the volume position connected to the analog input pin as a voltage; then, it converts to the blower’s operation time and displays on the OLED.
   2. Detect the ON/OFF switch connected to J1-9, 10 pins of the circuit diagram when pressing the start switch, turn on the blowers’ drive pin, activate the blowers, and turn on the LED during the operation.
   3. Control the blowers by PWM. Detect the position of the 10-kΩ variable resistor connected to the circuit diagram J1-5, 6, 7, and drive the blowers with the corresponding output.
   4. Detect the position of the 10-kΩ variable resistor connected to the circuit diagrams J1-1, 2, 3 pin by setting the drying time and activate the blowers for a time corresponding to that.
   5. Connect the power LED to the circuit diagrams J1-15, 16 pin. Connect the start LED to the circuit diagrams J1 – 12, 13.
      Note: The power LED lights up when the power turns on, and the start LED lights up while the blowers are activated.
   6. Connect the OLED to PB4, PB5 of the CPU with an I2C.
      Note: The operation time displayed on the OLED is counted down every second. When the operation time reaches 0, the blowers’ drive pin is set to 0, the blowers are stopped, and the operating LED is turned off to make the transition to the initial standby state.
   7. Use the Adafruit SSD1306 library for an OLED display of Arduino.
      Note: When the power switch is turned ON, operate in the order of initialization and message display. A part of the source code is shown below as an example of use of this library.
      #include "Wire.h";
      #include <Adafruit_SSD1306.h>
      #define OLED_RESET -1
      Adafruit_SSD1306 display(OLED_RESET);
      
      
      void setup() {
      Serial.begin(115200);
      while (!Serial) {
      ; // wait for serial port to connect. Needed for Leonardo only
      }
      Wire.begin(SDA, SCL); // (SDA, SCL)
      delay(1000);
      display.clearDisplay(); // Clear the buffer.
      display.setTextSize(1);
      display.clearDisplay();
      display.print(F("SD ")); // Weake Up Message Display(Version)
      display.println(ver);
      display.display();
      
      
      }

4. Method of Operation

1. See Figure 2 for details of the External View.
2. Turn the main power switch of number 10 ON. The operation lamp of number 11 lights up.
3. Place the optical cells on the mesh number 2 from the lattice part of the plastic of number 1.
   Note: The number of optical cells that can be mounted is as many as the number of lattices.
4. Select a two-blower operation or four-blower operation. Depending on the driving situation, the operation lamp of number 5 and number 6 lights up.
   Note: Number 3 is a switch for operating the blowers on the right side, and number 4 is a switch for operating the blowers on the left side.
5. Set the operation time with the timer with number 9.
6. Turn number 7 on.
   Note: The fan with number 12 starts, and, at the same time, the operation lamp of number 8 lights up.

5. Method to Measure the Drying Time

1. In the case of natural drying
   1. Wash the optical cells thoroughly with water or ethanol. Use thick absorbent paper to absorb the moisture of the optical cells, then move the cells to another place on the thick absorbent paper and wait until they dry.
2. In the case of the optical-cell dryer
   1. Wash the optical cells thoroughly with water or ethanol.
      Note: Use thick absorbent paper to temporarily absorb the moisture.
   2. Place the optical cells in the optical-cell dryer, then wait until they are dry.
   3. Measure the drying time 3x for each cell.
3. Comparison of the average values
   1. Measure the drying times 3x at 30 places to obtain the distribution.
      Note: This is to detect the time difference according to the position of the cells in the optical-cell dryer.
   2. Use average values of all 30 places for a comparison with water.
      Note: In the case of washing with water, determine the positions of the optical cells randomly, then measure the drying time at 10 points.