EE 1105/1305 – Intro to Electrical and Computer Engineering

Module 7 – Pressure Sensor

Week of November 16th, 2020

Name:________________________________ Group:_____________

IMPORTANT - READ CAREFULLY: Lab questions are now broken into PRE-LAB, LAB, and POST-LAB components. Please go to the EE1305 website and read the lab procedure, and complete all of the PRE-LAB sections, BEFORE coming to the lab.

Pre-Lab - Question 1:

· What is systolic pressure? Give an example of the value for systolic pressure in unit of mmHg.

· What is diastolic pressure? Give an example of the value for diastolic pressure in unit of mmHg.

Pre-Lab - Question 2:

· Think about design of a circuit capable of finding your blood pressure using the circuit blocks in Figure 4 of procedure 2. Draw a schematic of possible circuit you like to build.

Hint: There are an infinite number of possible good solutions. If you look at the last few labs you will see examples of low-pass, high-pass, and amplification circuits.

The high-pass filter and low pass filter should have a cutoff such that your pulse gets through, i.e. a 1 Hz signal.

NOTE: For this week’s lab, you are individually work for all procedures and everything should be completed by yourself. You are provided with necessary instructions.

Lab – Procedure 1: Follow the procedure 1 on the website.

· Include the model that relates voltage from blood pressure sensor to pressure. Define each parameter in the model.

You can find this formula in procedure 1, please read this procedure to define each parameter and explain what is Vout? Vs? and P?

Vout = Vs(0.018P + 0.04)

· Solve for Pressure (P) in the equation, and include unit conversions in order to end up with units of mmHg.

Solution: I isolated pressure (P) and wrote expression for pressure (P) as function of Vout. You know that Vs= 5V and pressure (P) is in the unit of kPa. In last equation, replace question marks with the appropriate value to convert the unit of pressure (P) from kPa to mmHg. First convert kPa to Pa, and convert Pa to mmHg (1.013 x 105 Pa = 760 mmHg).

Lab – Procedure 2: Please follow procedure 2 to analyze and build blood pressure circuit.

· Design your circuit and draw schematic. Include all calculation you performed to determine the value of each component in your circuit.

The systolic pressure is a result of the maximum pressure exerted by the heart on the arteries during contraction of the heart muscle, and the diastolic pressure is the pressure exerted by the heart in between beats on the arteries. In order to extract the systolic/diastolic pressure, we need to measure and analyze the pulsation caused by heart muscle using the pressure sensor. The heart signal has frequency around 1 Hz. We need to use low pass filter and high pass filter to filtered out noises and detect the desired heart signal with frequency of 1 Hz. We need to use Op-Amps that act as a buffer between elements such that each functional block can be built and tested in isolation. At last stage, we need to use an amplifier to get a reasonable level for the output signal.

The low pass filter should be design with fc a little bit higher than 1Hz (suggestion is fc= 15.9 Hz) in order to allow 1 Hz heart signal to perfectly pass through the filter and also remove high frequency noises. And high pass filter should be design with fc a little bit lower than 1Hz (suggestion is fc= 0.32 Hz) in order to allow 1Hz heart signal to perfectly pass through the filter and remove low frequency noises. For the last stage, we suggest you to design an inverting amplifier with gain of -33 which is big enough to see a reasonable level for the output signal.

Use above information to calculate the value of C1, R1, C2, R2, C3, R3, R4, and R5 here:

· Use your hand to draw the bode plots of high pass filter and low pass filter included in the circuit you designed. The graph should include x label, y label and please mark where the fc is placed. You can draw the bode plot on a sheet and then use your cell phone to take a picture of that and include here.

· Build your circuit. Put your UTEP ID across your breadboard and take a picture of your UTEP ID and final circuit on your breadboard, and include it in your report.

For high pass filters, use the resistor of 56 kΩ which is the closest on to 50 kΩ.

· Take screen shot of your Voltage vs time data after each stage of the circuit, including both Ch1 and Ch2 data.

You can follow the instruction for this procedure by watching this video:

https://minersutep-my.sharepoint.com/:v:/g/personal/mshokrekhod_miners_utep_edu/EQ-vrjjWm-ZAhOvOcmhVNxkBrzHq8SfOgyy6jJjWCwfoZQ?e=Cio6Hn

· Plot Pressure vs time for the input signal.

You can watch the video to complete this part. Please read below for your information:

Ch1 measures the input signal which is the raw voltage data from the pressure sensor. Export Ch1 data and save it in .csv format with name of lab7data. Then import lab7data in MATLAB. The imported file (lab7data) has two columns, the first column is time and second column is voltage data from the pressure sensor. Use the formula you obtained in procedure 1 to convert second column (lab7data(:,2)) to pressure. And plot pressure vs time.

· Determine the Systolic Pressure, the Diastolic Pressure, and the Mean Arterial Pressure from your Pressure vs time figure.

You can watch the video to complete this part. Please read below for your information:

Look at signal that you measured at output of last stage using Ch2. Find the time where the pulsation starts to appear. Then look at the plot of Pressure vs time (the one you plotted in Matlab) and read pressure at this time. This value of the pressure is called systolic pressure.

Look at signal that you measured at output of last stage using Ch2. Find the time where the pulsation intends to be stopped. Then look at the plot of Pressure vs time (the one you plotted in Matlab) and read pressure at this time. This value of the pressure is called diastolic pressure.

Look at signal that you measured at output of last stage using Ch2. Find the time where the amplitude of pulsation is maximum. Then look at the plot of Pressure vs time (the one you plotted in Matlab) and read pressure at this time. This value of the pressure is called “Mean Arterial Pressure”.

Post- Lab – Step 1 Organize all of your Figures and tables neatly in your Word document. Figure caption is placed at the bottom while table caption should be placed on top of the table. For any figure you copy from website, please include reference number at the end of figure caption. Then cite to the website in Reference section of your report.

Post- Lab – Step 2 In a few sentences, answer the following sentences. You can also answer them in your Word doc if you want to type/need more room.

· In procedure 2, describe each stage of your circuit, the cut-off frequencies, and whether it is a high pass filter, low pass filter or amplifier (using Bode plots). Explain what you expect to happen to the signal after each filter. Refer to your Bode Plot figures in your explanation

Post- Lab – Step 3 In a few sentences, answer the following sentences. You can also answer them in your Word doc if you want to type/need more room.

· Explain how did you determine the systolic pressure?

· Explain how did you determine the mean arterial pressure?

· Explain how did you determine the mean diastolic pressure?

Post- Lab – Step 4 Extra Credit:

Draw the schematic of your circuit using the Digikey Schematic Software. Link of access is https://www.digikey.com/schemeit/project/

Post- Lab – Step 5 Include the Figures, add your answers and solutions in this document. Upload this document in the respected folder in the blackboard for grading.