CHAPTER 3

CHAPTER 3

METHODOLOGY

This chapter focusses on the methodology to develop the device, discussing on steps, theories and components involved in each part of the system. The project is divided into two parts; hardware and software. The hardware part includes the circuit design for the near infrared sensor and the LCD keypad shield. While, the software part consists of the operational flow of the microcontroller. The glucose calibration experimental procedures are also discussed in this chapter.

3.1

Project Overview

Figure 3.1 illustrates the block diagram of the proposed portable non-invasive glucose monitoring system. The system starts operating once the transmitter

(in Figure 3.2) transmits an infrared signal which is exposed to the glucose solution or blood sample. The glucose molecule in the glucose solution or blood sample reflects the infrared signal to the receiver (photodiode). The photodiode (in Figure 3.3) receives the infrared signal which is converted to an equivalent voltage value. The Arduino Uno microcontroller, uses these voltage value as a parameter to calculate the glucose concentration and determine the insulin dose needed corresponding to the user’s body mass index (BMI). Finally, the measured glucose concentration and insulin dose will displayed on the LCD screen.

Figure 3.1: Block diagram of the portable non-invasive blood glucose monitoring device

3.2

Hardware Design

The main hardware components in the system consists of five (5) parts which includes a transmitter (LED1550E), a photodiode (FGA10), an operational amplifier (OP491), microcontroller (Arduino Uno), and a liquid crystal display (LCD) keypad shield.

3.2.1

Near Infrared (NIR) Detection Circuit

The NIR detection circuit consists of a transmitter circuit and a receiver circuit (as shown in Figure 3.4a and Figure 3.4b respectively), with both transmitter and receiver positioned side by side and points to a reflective surface. both transmitter and receiver operates at 5V and is powered by the Arduino microcontroller[27]. The transmitter (LED1550E), as shown in Figure 3.2 is an ultra-bright NIR LED which emits infrared light with a spectral output between 1400 nm-1700 nm centred at 1550 nm. Referring to the data sheet in Appendix C, it is composed of heterostructures which is grown on Indium Gallium Arsenide Phosphide (InGaAsP) substrate and is encapsulated in a 5 mm (in diameter) hemispherical clear epoxy casing. The maximum reversed voltage or the maximum output voltage of the NIR is 5V[27].

Figure 3.2: Transmitter (LED1550E)

Figure 3.3: Photodiode (FGA10)

The receiver circuit (as shown in Figure 3.4b) consists of a photodiode, a noise filter and an operational amplifier. A low pass filter is connected to the voltage source to reduce the noise frequency from the source. The FGA10 photodiode is suitable to be used with the transmitter as it has a wavelength sensitivity which is within 800 nm1800 nm[28]. The photodiode is used to measure continuous wave fibre light source and converts the optical power received from the transmitter to an electrical current value. In this project, the electrical current is converted into voltage by placing a load resistor (RL) at the anode as shown in Figure 3.4b.

The value of the output voltage depends on the intensity of the infrared signal it receives, which is between 0 V to 5 V. Since the output voltages from the photodiode are usually less than 1 V, an operational amplifier is used to amplify the output signal. Figure 3.4 (b) shows the complete schematic diagram of the detection circuit.

(a)

(b)

Figure 3.4: Schematic diagram of the NIR detection circuit. (a) Transmitter (b) Receiver (photodiode) circuit.

circuit.

3.2.2

Implementation of LCD Keypad Shield

The LCD keypad shield, as in Figure 3.5 is developed to be used with any

compatible Arduino boards. It consists of six (6) momentary push buttons and a 2x16 LCD screen. It does not require any soldering, only to be plugged to the main Arduino board. Pin 4 to pin 9 of the main Arduino board is used to control the LCD display, while pin 8 and pin 9 are used for Register Select (RS) and Enable pin. The LCD keypad shield is used to key in the height and weight of the users and also to display the measured glucose concentration and calculated insulin dose needed. Figure 3.6 (a) and (b) show the schematic diagrams of the push buttons and the LCD screen.

(a )

Figure 3.5: LCD Keypad shield

(b)

(b) Figure 3.6: Schematic diagram of the (a) push buttons (b) LCD screen

3.3

Software Development

The main focus of the software development is the microcontroller. The Arduino Uno is a microcontroller board based on Atmega328 and has 14 digital input and output pins. It can be powered by a (5 V-12 V) battery or by simply connecting it to a computer with a universal serial bus (USB). The Arduino Uno is used as the controller for the device as it is an open source which is easy to code and upload to the input/output (I/O) board. The open source Arduino code is known as integrated development environment (IDE) and its interface is shown in Figure 3.7.

Figure 3.7: IDE software interface and serial monitor (right)

The microcontroller supplies voltages to bias both transmitter and photodiode. The output of the photodiode and amplifier are connected to the analogue pin of the microcontroller. The block diagram of the Arduino and the detection circuit is show in Figure 3.8. Meanwhile, Figure 3.9 displays the connection of the LCD keypad shield and Arduino.

Figure 3.8: Block diagram of Arduino and detection circuit

Figure 3.9: The connection of LCD keypad shield and Arduino

In this project, the Arduino Uno microcontroller is used to calculate the concentration of glucose as well as the required insulin dose, corresponding to the body mass index (BMI) of the users. The output voltage obtained from the photodiode is used as a parameter to determine the glucose concentration by using a mathematical equation acquired from the glucose calibration experiments.

Figure

3.10 illustrates the flowchart of the glucose and insulin calculation. The BMI values are divided into three groups; underweight (BMI<25), normal (25≤BMI≥30), and overweight (BMI>30). The data are based on subcutaneous insulin order set of Banner Good Samaritan Medical Centre, Phoenix[29].

Firstly, the user is required to enter their height and weight. The user’s BMI will be calculated to determine whether the user is in the underweight, normal or overweight category. The sensor will then start to measure the glucose concentration of the glucose solution sample. If the measured glucose concentration is less than 70mg/dL, no insulin is needed for the user. However, if the measured glucose concentration is more than 70 mg/dL, a corresponding insulin dose is needed, (based on the tables for each BMI category in the flow chart). Both values of measured. glucose concentration as well as the required insulin dose will be displayed on the LCD screen.

Start

Enter Height & weight

Calculate Body Mass Index BMI=

No

BMI<25

No

25≤BMI<30

Yes

Yes

Get glucose level

Yes Get glucose level

Get glucose level

Glucose <70

No

Glucose <70

BMI≥30

No

Glucose <70 Yes

Yes Yes No insulin

No insulin

Glucose Level (mg/dL) 70-150 151-175 176-200 201-225 226-250 251-275 276-300 >300

Insulin dose (Units) 0.4 1.4 2.4 3.4 5.5 7.5 9.4 12.4



No insulin


Figure 3.10: Flowchart of the microcontroller


No

3.4

Experiment Procedure

Two (2) sets of experiments were conducted to determine the relationship between glucose concentration and the sensor’s output voltage. Several glucose solutions of different concentrations ranging from (10mg/dL-320mg/dL) were prepared by dissolving glucose (dextrose monohydrate) in 1 dL of distilled water, as shown in Equation 3.1 and Equation 3.2. The solutions were prepared in tinted amber reagent bottles as shown in Figure 3.11 to avoid them from being affected by the light.

1dL = 100ml (Equation 3.1)

100 mg/dL = 100mg of glucose+100ml of distilled water (Equation 3.2)

30 ml of each glucose solution were transferred into a cuvette and positioned between the transmitter and receiver, as shown in Figure 3.12. The output voltages for different glucose concentrations were recorded to determine the relationship between glucose concentration and the sensor’s output voltage. In addition, a reliability test was carried out by comparing the glucose concentration measurements from four subjects using invasive finger-prick techniques (Accu-Check) and the proposed portable noninvasive device.

CHAPTER 3

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