Development of Electronic Reader for Biosensor (Glucose Sensor)

1.1 Introduction

In this chapter, it discussed the overall flow of this project. Based on the techniques and system in chapter 2, the chosen one is applied and explain in this chapter. First is, the flow of project system from the device to switch on until it display the value. The overall project is shown using the flowchart with the explanation. Then it discussed the hardware design system and how it operates.


The hardware design system is discussed and illustrates using the block diagram. The component used and how it operates is explained briefly. There are also given the full specification of the component such as LMC6484IN Quad Op-Amp, the preprocessing circuit and the Arduino UNO microcontrolller.


1.2 Project Flow and Hardware Components

In the making of the electronic design project, few things need to be consider to make sure that a project is done within a given period. Planning of work need to be made before starting a project. The most important thing is project flow. Project flow need to be created so that the view of the project is better and clear. Other thing that need to be consider is the project hardware development.


The hardware flow is needed to make sure the hardware design is working properly and like the desired one. Each component of the hardware need to be understood and also need to know their behaviou\r. It is important to know how they work so that when problems occurs, it can be fix as soon as possible.


1.2.1 Project Flow




Figure 3.1 Electronic Reader Project Flow

Figure 3.1 is the flow chart of how the electronic reader works. When the device is turn on, place the test strip on the connector. The blood sample taken from finger using the finger prick method is place on the test strips. The test strip used act as a biosensor. The test strips will produce analog signal reading sense by the preprocessing circuit that connected to Arduino. Arduino then convert the analog signal to digital signal to be process. After the Arduino process the signal, it sends the converted data to OLED display via I²C protocol. The data converted is the measurement of the glucose level in the blood and displayed on OLED display.


1.2.2 Design System Flow





Figure 3.2 Flow Chart of the Design System


Figure 3.2 shows the flow chart of the design system. When the system start and initialize, the OLED display will show “Welcome to E-Reader, Insert Strip and Press >”. The system will wait for the test strip to be inserted into the strip connectors. After the strip is inserted, press the push button and OLED dislay will show “Please Put Blood in Test Strip”. It will wait for the sample. After it sense the presence of sample, OLED display will show count from 5 to 1 and then it display the voltage and glucose measurement in mg/dl and mmol/L. it will remain showing the latest result until the reset button is pushed.


1.2.3 Hardware Block Diagram



Figure 3.3 Block Diagram of the Hardware
 

 

Figure 3.3 is the block diagram of the hardware design. The biosensor used is glucose test strips and electrochemical test strips and it is connected to the preprocessing circuit. The preprocessing circuit consist of few important components such as operational amplifier, capacitor, resistor and preset type variable resistor. The preprocessing circuit will detect the analog signal from the test strip and amplify the signal and then send to microcontroller to process the data. The microcontroller used is Arduino UNO R3 with ATMega328 as its processor. The processed data from the UNO is then display using OLED display via I²C protocol. The processed data shown on OLED display is the measurement of the blood glucose level. The power source used is battery Li-Po Power Shield.


1.2.4 Biosensor

The glucose test strips and electrochemical test strips act as the biosensor of this project. It uses biological or living material for its sensing function. There are three parts of a biosensor;

1) Biological detection elements - recognize the biological material
2) A transducer - converts the biorecognition event into a measurable signal
3) Signal processing system - converts the signal into a workable form.

The oxidation of glucose to gluconic acid is based on the enzyme glucose oxidize (GOx) that act as the catalyst. The biorecognition element is the enzyme that recognize the glucose molecules. The enzyme molecules are located on an electrode surface (the transducer). When the enzyme recognizes the glucose molecules, it act as a catalyst to produce gluconic acid and hydrogen peroxide from glucose and oxygen from the air. The number of electron transfer due to hydrogen peroxide is recognizes by the electrode. The electron flow is proportional to the number of glucose molecules present in blood. It produces an electrical current which is proportional to the blood glucose concentration [8]. Therefore, as the blood sample is place on the electrode of the test strips, the reaction occurs as the explanation.



Figure 3.4 One Touch Ultra Test Strips


Figure 3.4 shows the test strip used for this project. Usually three electrodes are printed into the test strips: a reference electrode, a counter electrode and a working electrode. A fixed voltage is applied and the resulting current after the blood is applied is monitored. The current response is then related to the glucose concentration through calibration. Since test strips may vary from batch to batch, some models require the user to manually enter in a code found on the vial of test strips or on a chip that comes with the test strip. By entering the coding or chip into the glucose meter, the meter will be calibrated to that batch of test strips. One Touch Ultra, the brand of test strips used for this project, has standardized their test strips around a single code number, so that, once set, there is no need to further change the code in their older meters, and in some of their newer meters, there is no way to change the code. Figure 3.5 shows the One Touch Ultra test strip connections.



Figure 3.5 One Touch Ultra Test Strip Connections

The electrodes are coated such that an enzymatic chemical reaction occurs at the electrode surface and this reaction dictates the resulting current. The details of the electrochemistry can be quite complex. Since commercial strips are used for this project, the details are unknown as the companies do not release detailed data about their particular test strips operation. Some devices apparently watch the current after a short initial transient (the current will level out to some degree) and then report the current after a fixed time. Another principle looks at the total amount of reaction which has occurred and thus integrates the current with respect to time to obtain the total amount of chemical reaction which has occurred. For this project, the data signal is taken when the average highest current occur so that it will be the current that produced from the test strip.


1.2.5 Test Strips Connector

Each type of test strips will fit only into their respective glucometer. So for this project, test strip connectors is being made DIY because that the connectors is really hard to find and need to specially order. Since that the commercial connectors is simple to make, the connectors made by using some pins, a board and some hot glue. Figure 3.6 shows the DIY test strip connectors.



Figure 3.6 Test Strip Connectors


The connector pins represent the electrode of the test strip. Figure 3.6 also shows the connectors pins without test strips attached to it.




Figure 3.7 Test Strips Attached with the Test Strip Connectors


Figure 3.7 shows the test strip attached to the strip connector. The connector is design for the test strip of this type and brand only.


1.2.6 Preprocessing Circuit

The preprocessing circuit used and designed to amplify the signal produced by the test strip and then send to the Arduino to process. Figure 3.9 shows the complete preprocessing circuit that have been soldered onto the Arduino Proto Shield along with the push button.so that it can fit and can be plug on the Arduino without any long jumper.



Figure 3.9 Complete Preprocessing Circuit Soldered on the Arduino Proto Shield


1.2.7 The Microcontroller

The microcontroller used for this project is the Arduino Uno. The Arduino UNO act as the brain of this device to execute the programming. It is a microcontroller board based on ATMega328 that comprises 14 digital pin entries act as input, 6 analog production entries act as output, a 16 MHz ceramic resonator, USB connection, power jack, ICSP header, and reset button. The board is equipped with the features needed to support the microcontroller by connecting it to a computer using a USB cable. The UNO can be powered via the USB connection or with an external power supply. External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Figure 3.10 shows the picture of the Arduino UNO.



Figure 3.10 The Arduino Uno


Table 3.1 Specifications of the Arduino UNO



Table 3.1 shows the specifications from the datasheet of the Arduino Uno. Basically, the test strip produce the analog signal reading that have been sense by the preprocessing circuit. It then send the signal reading to the microcontroller which is Arduino UNO to convert the analog signal to digital signal to be process further. The coding set in The UNO will convert the signal so that it will come out with the measurement value of the glucose level. The software use to set the UNO is IDE software. It’s the software to install coding in the processor. However, before the data send to display, it will rerun automatically for 10 times to get the average reading of the measurement. This is to overcome the mathematical error from the sensor and the processing circuit. The data processed are then for displaying. The display use is Organic Light Emitting Diode (OLED) display with I²C protocol.

1.2.8 The Display



Figure 3.11 Organic Light Emitting Diode (OLED) 128x64 Display


Figure 3.11 shows the OLED 128x64 display. As for the display for this project, OLED 128x64 display is used. Organic Light Emitting Diode (OLED) is a 128x64 resolution and 0.96 inch display. The display is same with the average mobile phone display. There are no back lighting with near 180º viewing angle. It uses the I²C interface and it is compatible with the Arduino that use as the microcontroller. The OLED display will display the value of the glucose level in mg/dl and mmol/L. The block diagram of OLED display is in Appendix A.


1.2.9 Power Supply

To make sure the hardware and whole system can operate in full power, the power supply chosen must have enough battery and power. There are two options in selecting the power supply, first is using the direct cable from Arduino connected to USB that have power source and second is by using the Li-Po (Lithium Polymer) power shield.




Figure 3.12 Li-Po Power Shield


Figure 3.12 shows the Li-Po power shield used for this project. The shield itself is a battery charger and designed to stack perfectly on Arduino UNO R3 or other compatible boards. It provides 5V power to Arduino main board. Basically any Arduino board that have similar layout as Arduino UNO can stack this shield onto it. The shield only uses the power pins which are the 5V and GND, the Digital IO and Analog pins are free to be used by other shields. It comes with 5V DC to DC booster, boosting the voltage of standard LiPo battery (3.0V to 4.2V) to 5V for Arduino usage. Besides, it also come with LiPo battery charger via USB micro-B receptor and it can be charge like a power bank and utilize the USB micro-B cable. The onboard boost converter can provide at least 1000mA current and output peak current at 1100mA. The booster itself come with over current protection. Not only that, the shield is also added the battery under voltage protection to prevent the battery to discharge under voltage and further damage. This shield also come with the ON/OFF switch because of the arduino doesnt have it’s own switch.