Strain gauges are used to measure the strain or stress levels on the materials. Alternatively, pressure on the strain gauge causes a generated voltage and it can be used as an energy harvester. You will be given either the flapping or tapping type gauge. When you test the circle buzzer type gauge, you will lay it flat on the table and tap on it. If it is the long rectangle one, you will flap the piece to generate voltage.
1. Connect the oscilloscope probes to the strain gauge. Record the peak voltage values (positive and negative) by flipping/tapping the gauge with low and high pressure. Make sure to set the oscilloscope horizontal and vertical scales appropriately so you can read the values. DO NOT USE the measure tool of the oscilloscope. Adjust your oscilloscope so you can read the values from the screen. Fill out Table 1 and provide photos of the oscilloscope.
Table 1: Strain gauge characteristics
Low:
Minimum voltage:-2V
Maximum voltage:3V
High:
Minimum voltage:-40V
Maximum voltage:45V
Image 1: Shows the output of the strain gauge
Image 2: Shows the output of the strain gauge
2. Press the “Single” button below the Autoscale button on the oscilloscope. This mode will allow you to capture a single change at the output. Adjust your time and amplitude scales so you have the best resolution for your signal when you flip/tap your strain gauge. Provide a photo of the oscilloscope graph.
Image 3: Shows the use of the "single" button
1. Construct the following half-wave rectifier. Measure the input and the output using the oscilloscope and provide a snapshot of the outputs.
Image 4: shows the output of the halfway rectifier
2. Calculate the effective voltage of the input and output and compare the values with the measured ones by completing the following table.
Effect (rms) Values Calculated Measured
3.535 Input 3.72
2.5 Output 2.15
3.535 Input 3.72
2.5 Output 2.15
3. Explain how you calculated the rms values. Do calculated and measured values match?
(Come back)
4. Construct the following circuit and record the output voltage using both DMM and the oscilloscope.
| Column1 | Oscilloscope | DMM |
| Output Voltage (p-p) | 2.4 | 1.848 |
| Output Voltage (mean) | 2.84 | 2.79 |
Table 1: Shows the output voltages using the different devices
5. Replace the 1 µF capacitor with 100 µF and repeat the previous step. What has changed?
| Column1 | Oscilloscope | DMM |
| Output Voltage (p-p) | 120 mV | 62.2 mV |
| Output Voltage (mean) | 3.27 | 3.22 |
Table 2: Shows the output voltages for thee 100uf capacitor
1. Construct the half-wave rectifier circuit without the resistor but with the 1 µF capacitor. Instead of the function generator, use the strain gauge. Discharge the capacitor every time you start a new measurement. Flip/tap your strain gauge and observe the output voltage. Fill out the table below:
| Tap frequency | Duration | Output Voltage |
| 1 flip/second | 10 seconds | 617 mV |
| 1 flip/second | 20 seconds | 1.37 |
| 1 flip/second | 30 seconds | 3.07 |
| 4 flip/second | 10 seconds | 3.29 |
| 4 flip/second | 20 seconds | 4.84 |
| 4 flip/second | 30 seconds | 8.8 |
Table 3: Shows the output for flips per second
2. Briefly explain your results.
As the flips increased in speed and in a longer duration, the voltage all increased from there, the faster you tap for the longer amount of time will give you higher outputs.
3. If we do not use the diode in the circuit (i.e. using only strain gauge to charge the capacitor), what would you observe at the output? Why?
If we didn't use a diode, the circuit would not work because the capacitor would immediately discharge and there would be no built up charge.
4. Write a MATLAB code to plot the date in table of Part C1.
D=[10,20,30];
Va=[0.617,1.37,3.07];
Vb=[3.29,4.84,8.8];
plot(D,Va,'--r')
hold on
plot(D,Vb)
legend('1 flip/second','4 flip/second')
xlabel('Duration (s)')
ylabel('Output Voltage (V)')
title('Half-wave recitifier')
