Engineering 44 SLee: 2013

MOSFETS

Objective
The purpose of this experiment is to learn how to use a MOSFET to control the speed of a motor. By only input some small voltage to the MOSFETS, it output relatively large current. We also use a potentiometer to control the input voltage.

Procedure
Part 1

The goal is to turn on and off the motor by controlling the pot. When we turning the pot, we changing the voltage across the motor and the MOSFET.

Part2:

We replace the pot with a Function Generator. The FG produces Square Waves, and duality was on

here is a video we took

http://www.youtube.com/watch?v=XJQfYBNOdgo&feature=youtu.be

Conclusion:
The lab was successful. Both ways controlled voltage, but part 2's method allowed for better speed control than part 1 with the pot. Using the oscilloscope get more detial, not only faster or slower, but also stop and irregular.

Freemat

Objective

Learn how to use freemat to solve complex number equeation

Calculation by hand

Sovle by freemat:

Conclusion
Freemat is a very useful tool to solve complex equation. In AC circuit, the impedance usually contains a imaginary part and as I showed, it is takes many steps to solve this kind of problem by hand. Freemat let this problems become very easy.

Oscilloscope

Purpose:
The purpose of this experiment was to study using an oscilloscope to detect and adjust different waveforms.

Introduction:
An Oscilloscope is an electronic device that is used to display time-varying signals and make appropriate measurements. In this experiment, we are going to explore the oscilloscope by varying the signal input with different amplitudes, frequencies, and shapes.

Experiment:

A sinusoid waveform was generated by the generator.

Period: 200 micro seconds

Peak-to-Peak Amplitude: 11.4V

zero-to-peak amplitude: 5.8V

aniticipated RMS value: 5.336V

The VDC and VAC RMS values of the generator were measured:

     VDC = 2.8mV
     VAC = 3.35 V

     VAC value was close to the anticipated RMS value.


    DC Offset

We add an offset of 2.5 V, and another one at 5V

DC Coupling at 5V

AC Coupling at 5V

The difference is that we can see the offset in DC coupling while nothing changes in AC.
2.5V offset measurements:
VDC = 2.51 V
VAC = 3.37 V
The VDC shows the offset in the output like the graph while the offset does not affect VAC.

    Square Waveform

   A square waveform was generated by the generator.

The VDC and VAC RMS values of the generator were measured:

        VDC = 10mV
        VAC = 5.33 V

        Compared to expected VAC measurement, VAC = 5V, the measured VAC value was close to the theoretical value.

      Mystery Signals

      A mystery signal was adjusted and measured during the lab. After a while of adjusting, the final waveform is shown below:

The more accurate waveform is:

      DC Voltage: 460 mV
     Frequency: 70Hz
     Pk-Pk Amp: 940 mV

Conclusion

     This experiment was successed. The results are changing voltage and frequency can making ddifferent graph. The new digital oscilloscope is much better than the heavy traditional ones.

Op Amps II

Objective

The purpose of the lab is explore the effects of a varying input voltages, and feedback resistors on the output voltage on an inverting Op Amp.

The following circuit was required to build in this experiment

Gain=-10=-Rf/R1

we know R1=10k

so Rf =100k

A measured voltage of 0.24 V obtained from the voltage divider in this experiment.

The circuit was built and connected according to lab manual

An 1k resistor was connected across the op-amp output.

Data Table

V_in (Desired)	V_in (Actual)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)
0.25 V	0.24 V	-2.41 V	2.46 V	-0.0246 mA
0.5 V	0.50 V	-4.90 V	4.87 V	-0.0502 mA
1.0 V	1.00 V	-10.04 V	9.86 V	-0.1028 mA

I_cc = 0.874 mA
I_ee = -0.981 mA
I_cc + I_ee = -0.107 mA
P_cc = V*I = 10.488 mW
P_ee = 11.772 mW

Extra Credit

R_f was replaced to obtain a gain of -5, and the determined value of R_f was 49.9k Ohms.

Data was measured when V_IN = 1 V

The gain becomes -5 when R_f = 50 kΩ

Measured R_f = 49.9 kΩ

V_in (Desired)	V_out (Measured)	V_RF (Measured)	I_op (Calculated)	I_cc (Measured)	I_ee (Measured)
1.0 V	-5.03 V	4.99 V	-0.101 mA	0.885 mA	-0.985 mA

I_ee + I_cc = -0.1 mA

Conclusion

We learned how to explore the effects of a varying input voltages, and feedback resistors on the output voltage on an inverting Op Amp. This experiment was very successful. The measured result is close to expected values, and it is consistent with Kirchhoff's Current Law. The results are as expected because the ratio of the feedback resistors gives a gain of -10. V_in does not change the gain, only the resistors. KCL held, so the experiment was a success. To get a gain of 5, the ratio of R_i:R_f had to be 1:5, therefore R_f = 50 kΩ. The gain of an inverting Op Amp is always equal to -Rf/Rin. If the gain is -5, the ratio of Rf/Rin has to be 5. As the same time, the current at the operating point is equal to the sum of the two rails coming into the op amp, and the KCL always holds correct.

Op Amp - Temperature Sensor (extra credit)

Objective

The purpose of this lab is to connect Op Amps to temperature sensor so that it can measure temperature from 15 °C to 35 °C with a resolution of 0.1 °C.

For each 1mV of input voltage, the amplified circuit should output 25mV.

Therefore, gain=25/1=25

We design the circuit as shown

(We use a difference op amp to subtract 150mV from the input voltage.)
To obtain 150 mV voltage, a voltage divider was used. According to calculation, the ratio of two resistance in the voltage divider was 19:1.

Voltage Divider

150mV=(1/20)*3V (3V is the power supply)

Therefore, we need 19k and 1 k resistors connect in parallel.

The actual voltage we got was 157.6 mV

Difference op amp

Our circuit

When we input a voltage of 1V into the circuit, the output voltage was measured to be 5V.

Conclusion

With a difference op-amp circuit, this experiment was successfully completed. It achieved the goal that to allow the system to measure 15 °C to 35 °C.