Glucometers play an important role in managing a diabetic patient’s health issues. Typically, the patient inserts a disposable test strip into the meter, pricks their finger, loads a droplet of blood onto the test strip, waits a couple seconds, and then receives a reading of the current blood glucose level.
The designs available on the market today are costly, large, and power inefficient. The design proposed in this project uses the analog voltage signal generated by a blood drop on a customized glucometer strip to measure glucose levels. The signal is amplified and fed into a Dialog GreenPAK™ SLG46580V CMIC. The GreenPAK decodes the voltage signal and compares it with preset thresholds to determine the glucose level.
The glucometer blood test strip used in this design is a typical one available on the market. The GreenPAK design can be easily modified to adjust the threshold levels of different glucose ranges. We’ve also included Reset and Start functions to make the design more reliable.
Different glucometer blood test strips may have different connections, so be sure to check the connections before implementing this design.
Below we described steps needed to understand how the customized glucometer has been programmed. However, if you just want to get the result of programming, download GreenPAK software to view the already completed GreenPAK Design File. Plug the GreenPAK Development Kit to your computer and hit the program to design the device.
The hardware schematic is shown in Figure 1.
The external 7805 voltage regulator is used to generate +5 V from the +12 V DC Adapter.
When a blood droplet is placed on the glucometer strip, a short circuit is created between the reference electrode and the counter electrode. This allows U1 (SLG88104V) to act as a unity gain amplifier. The output voltage is equal to the input voltage applied at the ‘+’ terminal, i.e., 2.1 V.
This short results in current flow between the counter electrode (now at 2.1 V) and the working electrode. The magnitude of the current flow is proportional to the glucose level of the blood drop.
The op-amp U2 (SLG88104V) acts as transimpedance amplifier. The output voltage of this amplifier can be calculated with the following formula:
VOUT = [Current flow between the Counter and Working electrodes] * R1
The 100 nF capacitor C1 is used to maintain smooth voltage.
Op-amp U3 is another unity gain amplifier that maintains a constant voltage at its output. The purpose of using 2.5 V and 2.1 V in this circuit is to maintain a voltage difference of 400 mV across two of the test strip electrodes. This is necessary for the glucometer to function properly.
The output voltage of op-amp U3 is then fed to the SLG46580V’s Pin6, which is configured as an analog input/output.
Glucometer Blood Test Strip
A typical glucometer strip is shown in Figure 2. The connections of the test strip are:
● 1 - Reference electrode
● 2 - Counter electrode
● 3 - Working electrode
● 4 and 5 - Test electrodes. These two electrodes are used to detect that the strip is inserted in the slot reserved for the strip. These two electrodes are not necessary for the functioning of the glucometer.
The connections may vary for different vendor strips; however, there should always be a reference, counter, and working electrode.
In each test strip, there is an enzyme called glucose oxidase. This enzyme reacts with the glucose in the blood sample and creates gluconic acid.
The gluconic acid then reacts with another chemical in the testing strip, called ferricyanide. The ferricyanide and the gluconic acid combine to create ferrocyanide.
Once the ferrocyanide has been created, the current moves through the blood sample on the strip. The level of current allows the GreenPAK to read the level of ferrocyanide and determine...Read more »