Thermo-sensor Lab

Purpose: to amplify a thermo-sensor to a specific output range.

Preperation

     Given:

• A LM35 that produces 10 mV/°C.
• work between 15 °C to 35 °C.

Using a difference amplifier, we shifted the range produced from 150 mV - 350 mV to

0V - 5V.

 V_1 = 150 mV, V_2 is the range given by the LM35
 Our gain is a factor of 25 so, R_f = 150 kΩ and R_i = 6 kΩ.

Experiment

We built the following circuit:

V_1 was measured at the left potentiometer while V_2 was measured at the one on the right

We made

V_2 = 350 mV to verify it was working.

 V_out was measured to be 5.05 V

Conclusion

We amplified 350 mV into 5V by using a power supply and voltage dividers to represent the LM35 at 35 degree C. The lab was a success.

MatLab and Complex Numbers

Purpose: To understand how to work with complex numbers in MatLab.

Tutorial:

1) Example with simple functions

1. 
   
2. 
   

2) Finding Magnitude and Phase angle

Assignment 1)

Assignment 2)

Assignment 3)

Assignment 4)

Conclusion:  Matlab provides a quick and easy way to work with imaginary numbers and solve linear systems of equations.

MOSFET Control of an Electric Motor

Purpose: To control the speed of the motor with a MOSFET circuit.

Experiment: We set up the following circuit:

Varying the resistance on the POT varied the speed of the motor. Going below 3.9V made the motor stop.

The POT was replaced with a function generator producing square waves at 10kHz with duality on and the oscilloscope to see the motor voltage.

When the frequency was reduced to only a few hertz, depending on the voltage the motor turned on and off.

Conclusion: Changing the speed on the motor was as simple as varying the voltage on the motor. This could be done with a varying voltage supply (function generator) or varying resistance (POT). The function generator worked much better than the POT.

Second Order Circuit Problem Example

Purpose: To go through various steps to understand how to do a second order circuit problem.

Introduction: We went through the "Second Order Systems" example at http://www.mhhe.com/engcs/alexander2e/netan_tutorials/tutorials/tutmenu.htm

Example:

These problems are not so bad when you take it one step at a time.

Introduction to Oscilloscopes

Purpose: To introduce the purpose and how to work an oscilloscope.

Introduction:
      We will use the following:

• an Oscilloscope
• a Function Generator set to 5kHz sine wave and 5 Volts
• a DMM

Experiment:

     The oscilloscope was adjusted to show about 2 periods and above the x-axis. The period is 200 microseconds. The voltage was adjusted to have a peak-to-peak voltage of 5 volts. The was a measured DC voltage of 0V and an AC voltage of 1.05V.

     Next we set DC offset on the Function Generator measured a DC voltage of 2.517V and an AC voltage of 1.051V. It showed the following: 

     Next we had the function generator display square waves. The square waves gave a DC voltage of 2.516V and and AC voltage of 1.375V. The Oscilloscope displayed the following:

     Finally, we were given a mystery signal to identify. Once the oscilloscope was properly adjusted.we saw the following:

                                               

                                             

 From this we identified the signal as a time varying ramp function!

Conclusion: Oscilloscopes can show voltage in a circuit as well as how it varies with time. It can also calculate frequency and allows one to focus on certain parts of a signal.

Capacitor Charging/Discharging

Purpose: To observe the properties of a capacitors in their charging and discharging states.

Introduction: 
We have 2 different circuit models for the charging and discharging with Thevenin equivalent as shown:

We want to design build and test a circuit that does the following:

• utilizes a 9V power
• Employs a charging interval of 20s with a stored energy of 2.5mJ
• discharges the 2.5mJ in 2s

   To fulfill these requirements we have the following for charging resistance and capacitance:

       The peak discharge current and discharge and resistance were then calculated.

 Experiment:
     The actual charge and discharge resistances used are as follows along with the voltage source.

      The circuit was then built. For capacitance we used 3 capacitors is parallel and hooked up logger pro voltage sensors.

     The   Charging and discharging was recorded on logger pro.

     Data:

The charging curve:

     The capacitor charges up to about 8.5V. The reasons for it not charging all the way are a leak resistance which is inherent to every capacitor. The main reason for the biggest loss is that logger pro capped it off around this voltage.

The discharging curve:

     The capacitor doesn't completely discharge in 2 seconds but it is extreemely close.

Conclusion:

     The charging and discharging of capacitors is exponential and the time to make them discharge and charge can be easily controlled by changing the value of the resistance and/or capacitors.

Practical Question:

OP-AMPS II

Purpose: See the effect of changing the feedback resistor and input resistances.

Introduction:

We need to calculate the resistances necessary to get a gain of -10 and what the current coming out of the op amp would be if Vs were 1V:

 

Experiment:
We then build the circuit setting the Vs to 0.25 and vary it while recording the voltages across the input and output resistors. A voltage divider was used to get Vs .

The circuit was then built with a 1K Ohm load according to the following schematic:

The same data was recorded with this set up.

\Data:

    Inverting Op-Amp

     

Vin Desire(V)	V_IN Actual(V)	V_Out Measured(V)	V_Rf Measured(V)	I_op Calculated(mA)
0.25	0.26	-2.59	2.58	0.026
0.5	0.52	-5.18	5.18	0.052
1	1.01	-10.11	9.94	0.101

       For V_IN = 1V

       Measured I_cc = 0.867 mA
                Calculated P_cc = 12*0.867 mP = 10.404 mP
       Measured I_ee = -0.979 mA 

                 Calculated P_ee = 12*0.979 mP = 11.748 mP

       I_cc + I_ee = 0.112 mA
       The percent error is 12% therefore, it is consistent with KCL.

 

      Circuit with 1k Ohms load

    

Vin Desire(V)	V_Out Measured(V)	V_Rf Measured(V)	I_op Calculated(mA)	I_cc Measured(mA)	I_ee Measured(mA)
1	-10.02	9.77	0.1	0.877	-0.984

    For V_IN = 1V

    Measured I_cc = 0.877 mA
            Calculated P_cc = 12*0.877 mP = 10.524 mP
    Measured I_ee = -0.984 mA
             Calculated P_ee = 12*0.984 mP = 11.808 mP
     I_cc + I_ee = 0.107 mA
     The percent error is 07% therefore, it is consistent with KCL.

Conclusion:

    With percent errors of 12% and 7% this experiment is considered a success and obeys Kirchhoff's Current Law. We saw that the gain depends directly on Rf/Ri.